JPH11298332A - Digital signal processor and speaker system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital signal processor capable of obtaining digital output signals closer to the source digital input signals of acoustic signals or the like and a speaker system provided with the digital signal processor. SOLUTION: This digital signal processor is provided with an over sampling part 1 for increasing the sampling rate of the digital input signals Sin, an attenuation part 2 for reducing the level of sampling signals Sov corresponding to the level reinforced in a signal processing part 3, the signal processing part 3 for performing a desired level reinforcing processing and a level reduction processing to attenuation signals Sat and a noise shaping part 4 for executing a noise shaping processing to processing signals Spc corresponding to a level reduction processing in the attenuation part 2 and a level change processing in the signal processing part 3, reducing quantization noise without degrading quantization accuracy and generating digital output signals Sout.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal processing device for digitally processing an input signal, and more particularly to a digital signal processing device suitable for an audio system including a speaker. .

[0002]

2. Description of the Related Art Conventionally, a so-called DSP (Digital Signal Processor) is used to digitize an audio signal and digitally perform various processes on the digitized audio signal.
Processors called rocessors are becoming common.

[0003] Considering a case where a so-called graphic equalizer process for digitally reducing or enhancing only the level of an audio signal in a specific frequency band is executed in the DSP, if the reduction process is performed, When re-quantizing the sound signal subjected to the reduction processing, some lower bits are lost. In the above-mentioned conventional DSP, the lower bits are ignored and the subsequent signal processing is performed. I was This is because even if the lower bits are ignored, the characteristics of the reproduced audio signal are not significantly affected.

[0004]

However, in recent years,
With the increase in precision and functionality of audio devices, many users have come to prefer sound reproduction closer to the original sound. In this case, the lower bits in the conventional DSP are lost. There has been a problem that noise or distortion due to noise cannot be ignored.

[0005] With the increase in the accuracy and functionality of the acoustic device, there has been a need to further reduce so-called quantization noise generated when an acoustic signal, which is an analog signal, is converted into a digital signal. There is also a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a digital signal processing apparatus capable of obtaining a digital output signal closer to an original digital input signal such as an acoustic signal. And a speaker system for outputting a sound corresponding to the digital output signal.

[0007]

According to an aspect of the present invention, a digital input signal sampled at a preset input sampling frequency and input from the outside is provided. A signal processing unit such as a signal processing unit that performs a predetermined signal processing including at least a reduction processing for reducing a level of a predetermined specific frequency band in the digital input signal and generates a processed signal; Alternatively, the sampling frequency of any one of the processed signals is set to N times the input sampling frequency (N is a real number greater than 1).
Based on the noise shaping characteristics indicated by the setting signal, and quantizes the generated processing signal and performs noise shaping on the processing signal based on the noise shaping characteristic indicated by the setting signal. A noise shaping unit such as a noise shaping unit for generating a digital output signal, and a frequency-level characteristic of the signal processing,
Correcting the deterioration of the quantization characteristic that occurs when the processing signal is quantized, and increasing the increase in the quantization noise caused by the correction of the quantization characteristic to a frequency band higher than a half of the input sampling frequency. A setting unit such as a control unit that sets the noise shaping characteristic so as to generate the digital output signal by shifting to the digital output signal, and generates the setting signal.

According to the operation of the first aspect of the invention, the signal processing means performs signal processing on the digital input signal to generate a processed signal.

At this time, the sampling rate conversion means converts the sampling frequency of one of the digital input signal and the processed signal into an N-fold sampling frequency.

[0010] Then, the noise shaping means, based on the noise shaping characteristic indicated by the setting signal,
The generated processing signal is quantized and subjected to noise shaping to generate a digital output signal.

At this time, the setting means corrects the deterioration of the quantization characteristic caused when the processing signal is quantized in accordance with the frequency-level characteristic of the signal processing, and performs the quantization caused by the correction of the quantization characteristic. A noise shaping characteristic is set so as to generate a digital output signal by shifting an increase in noise to a frequency band higher than a half frequency of the input sampling frequency, and a setting signal is generated.

Therefore, the sampling rate of the digital input signal or the processed signal is increased, and the noise shaping process corresponding to the frequency-level characteristic of the signal processing is performed on the processed signal. It is possible to compensate for the dropped bit component due to the quantization, and to relatively reduce quantization noise in a frequency band lower than one half of the input sampling frequency.

According to another aspect of the present invention, there is provided a signal processing means for attenuating a digital input signal sampled at a preset input sampling frequency and inputted from the outside. In order to prevent the level of the increase / decrease signal processing in (2) from becoming higher than the level that can be processed by the signal processing means, the level of the digital input signal is reduced corresponding to the increase / decrease signal processing to generate the attenuation signal. Attenuating means such as an attenuating unit for outputting to said signal processing means; and augmenting processing for increasing a level of a predetermined first specific frequency band in said attenuated signal with respect to said attenuated signal; A preset second specific frequency different from the one specific frequency band The signal processing means such as a signal processing unit that generates the processed signal by performing the increase / decrease signal processing including at least one of the reduction processing for reducing the level of the band, the digital input signal, the attenuated signal or the A sampling rate conversion unit such as an oversampling unit for converting the sampling frequency of any one of the processed signals into a sampling frequency N (N is a real number greater than 1) times the input sampling frequency, and a setting signal. A noise shaping unit such as a noise shaping unit that quantizes the generated processing signal and performs a noise shaping process on the processing signal based on the noise shaping characteristic to generate a digital output signal, and the attenuating unit. Frequency-level characteristics of reduction processing In response to the frequency-level characteristic in the increase / decrease signal processing, the deterioration of the quantization characteristic caused when quantizing the processed signal is corrected, and the increase in the quantization noise caused by the correction of the quantization characteristic is calculated as Setting the noise shaping characteristic so as to generate the digital output signal by shifting to a frequency band higher than half the frequency of the input sampling frequency, and setting means such as a control unit for generating the setting signal. Prepare.

According to the operation of the second aspect of the present invention, the attenuating means reduces the level of the digital input signal corresponding to the increase / decrease signal processing in the signal processing means, generates the attenuated signal, and outputs the attenuated signal to the signal processing means. Output.

Next, the signal processing means performs an increase / decrease signal process on the attenuated signal to generate a processed signal.

At this time, the sampling rate conversion means converts the sampling frequency of one of the digital input signal, the attenuated signal and the processed signal into a sampling frequency N times the input sampling frequency.

[0017] The noise shaping means is provided based on a noise shaping characteristic indicated by the setting signal.
The generated processing signal is quantized and subjected to noise shaping to generate a digital output signal.

At this time, the setting means corrects the deterioration of the quantization characteristic caused when the processing signal is quantized in accordance with the frequency-level characteristic of the reduction processing in the attenuation means and the frequency-level characteristic of the increase / decrease signal processing. A noise shaping characteristic is set so as to generate a digital output signal by shifting an increase in quantization noise caused by the correction of the quantization characteristic to a frequency band higher than a half of the input sampling frequency. Generate a setting signal.

Therefore, the sampling rate of any one of the digital input signal, the attenuated signal and the processed signal is increased, and the frequency-level characteristic of the reduction processing in the attenuating means and the increase / decrease signal processing are performed on the processed signal. Since the noise shaping processing corresponding to the frequency-level characteristic of (1) is performed, even when the signal processing means performs the enhancement processing, it is possible to compensate for the bit component which is dropped due to the quantization of the processing signal whose level is reduced, Quantization noise in a frequency band lower than one half of the sampling frequency can be relatively reduced.

According to a third aspect of the present invention, a digital input signal sampled at a preset input sampling frequency and input from the outside is provided in advance in the digital input signal. One of an enhancement process for increasing the level of the set first specific frequency band and a reduction process for reducing the level of a preset second specific frequency band different from the first specific frequency band in the attenuated signal. In order to prevent the level of the digital output signal from exceeding a predetermined level, a signal processing unit such as a signal processing unit for performing a processing signal by performing at least an increase / decrease signal process, and outputting the processed signal to the attenuating unit, In response to the increase / decrease signal processing, the level of the processed signal is reduced, and an attenuation signal is generated to generate noise. Attenuating means, such as an attenuating unit, for outputting to the erasing means; and a sampling frequency of any one of the digital input signal, the attenuating signal, and the processed signal is set to N (N is greater than 1) of the input sampling frequency. A sampling rate conversion unit such as an oversampling unit for converting the sampling signal into a (real number) times sampling frequency, and quantizing the generated attenuated signal and noise shaping the attenuated signal based on a noise shaping characteristic indicated by the setting signal. A noise shaping unit such as a noise shaping unit that performs processing and generates the digital output signal, and corresponds to a frequency-level characteristic of a reduction process in the attenuating unit and a frequency-level characteristic of the increase / decrease signal process. Correcting the deterioration of the quantization characteristic caused when quantizing the attenuated signal, and increasing an increase in quantization noise caused by the correction of the quantization characteristic to a frequency band higher than a half of the input sampling frequency. And setting means such as a control unit for setting the noise shaping characteristic so as to generate the digital output signal and generating the setting signal.

According to the operation of the third aspect of the invention, the signal processing means performs increase / decrease signal processing on the digital input signal, generates a processed signal, and outputs the processed signal to the attenuation means.

The attenuating means reduces the level of the processed signal in accordance with the increase / decrease signal processing, generates an attenuated signal, and outputs it to the noise shaping means.

At this time, the sampling rate conversion means converts the sampling frequency of any one of the digital input signal, the attenuated signal and the processed signal into a sampling frequency N times the input sampling frequency.

[0024] The noise shaping means is based on the noise shaping characteristic indicated by the setting signal.
It quantizes the generated attenuated signal and performs a noise shaping process on the attenuated signal to generate a digital output signal.

At this time, the setting means corrects the deterioration of the quantization characteristic caused when the attenuated signal is quantized in accordance with the frequency-level characteristic of the reduction processing in the attenuation means and the frequency-level characteristic of the increase / decrease signal processing. A noise shaping characteristic is set so as to generate a digital output signal by shifting an increase in quantization noise caused by the correction of the quantization characteristic to a frequency band higher than a half of the input sampling frequency.
Generate a setting signal.

Therefore, the sampling rate of any one of the digital input signal, the attenuated signal and the processed signal is increased, and the frequency-level characteristic of the reduction processing in the attenuating means and the increase / decrease signal processing are performed on the attenuated signal. Since the noise shaping process corresponding to the frequency-level characteristic in the above is performed, even if the attenuation process is performed by the attenuating means in order to adjust the level of the digital output signal, the bit component dropped due to the quantization of the attenuated signal whose level is reduced is removed. Compensation can be made, and quantization noise in a frequency band lower than half the input sampling frequency can be relatively reduced.

According to a fourth aspect of the present invention, there is provided a digital signal processor according to any one of the first to third aspects, wherein the noise shaping means is set in advance. The apparatus further comprises dither addition means such as an adder for adding dither, wherein the setting means sets the noise shaping characteristic so as to compensate also for a noise component increased by the addition of the dither and generates the setting signal. Be composed.

According to the operation of the invention described in claim 4, in addition to the operation of the invention described in any one of claims 1 to 3, the addition means in the noise shaping means adds dither.

The setting means sets a noise shaping characteristic so as to compensate also for a noise component increased by the addition of the dither and generates a setting signal.

Therefore, the quantization noise can be converted into white noise by the addition of the dither, and the noise component increased by the addition of the dither can be removed.

In order to solve the above-mentioned problems, the invention according to claim 5 is to prevent the signal processing in the signal processing means for the attenuated signal from becoming higher than the level which can be processed by the signal processing means. Generating the attenuated signal by reducing the level of a digital input signal sampled at a predetermined input sampling frequency and input from the outside, based on a frequency-level characteristic preset corresponding to the signal processing. Attenuating means, such as an attenuating section, for performing the attenuating process on the generated attenuated signal to enhance the level of a predetermined specific frequency band in the attenuated signal based on a preset frequency-level characteristic. Reduce one of the reduction processes to reduce the frequency band level The signal processing means such as a signal processing unit that performs the preset signal processing including the above, and generates a processed signal; and sampling of any one of the digital input signal, the attenuated signal, and the processed signal. Sampling rate conversion means such as an oversampling unit for converting a frequency to a sampling frequency N times (N is a real number greater than 1) the input sampling frequency, and quantizing the generated processing signal;
Correcting the deterioration of the quantization characteristic that occurs when the processing signal is quantized corresponding to the frequency-level characteristic of the reduction processing in the attenuating means and the frequency-level characteristic in the signal processing, and correcting the quantization characteristic Performing a noise shaping process on the processed signal based on a noise shaping characteristic set in advance so as to shift an increase in quantization noise caused by to a frequency band higher than a half frequency of the input sampling frequency,
Noise shaping means such as a noise shaping section for generating the digital output signal.

According to the operation of the invention described in claim 5, the attenuating means reduces the level of the digital input signal based on the frequency-level characteristic set in advance corresponding to the signal processing in the signal processing means. Generate a signal.

The signal processing means performs signal processing on the generated attenuated signal based on a preset frequency-level characteristic to generate a processed signal.

At this time, the sampling rate conversion means converts the sampling frequency of any one of the digital input signal, the attenuated signal and the processed signal into a sampling frequency N times the input sampling frequency.

The noise shaping means quantizes the generated processing signal and quantizes the processing signal in accordance with the frequency-level characteristic of the reduction processing in the attenuating means and the frequency-level characteristic in the signal processing. Is set in advance so as to correct the deterioration of the quantization characteristics caused by the correction, and to shift the increase in the quantization noise caused by the correction of the quantization characteristics to a frequency band higher than a half of the input sampling frequency. A noise shaping process based on the noise shaping characteristics is performed on the processed signal to generate a digital output signal.

Accordingly, the sampling rate of any one of the digital input signal, the attenuated signal and the processed signal is increased, and the frequency-level characteristic of the reduction processing in the attenuating means for the processed signal and the signal processing means Since the noise shaping processing corresponding to the frequency-level characteristic of the signal processing is performed, it is possible to compensate for the bit component dropped by the quantization of the processing signal whose level has been reduced, and to reduce the frequency of the input sampling frequency by half. The quantization noise in a low frequency band can be relatively reduced.

According to a sixth aspect of the present invention, a digital input signal sampled at a preset input sampling frequency and input from the outside is provided in advance in the digital input signal. A signal processing unit or the like that performs a preset signal process including at least one of a reduction process for reducing the level of the set specific frequency band and an enhancement process for increasing the level of the characteristic frequency band, and generates a processed signal. Signal processing means, and an attenuating section for reducing the level of the processed signal corresponding to the signal processing and generating an attenuated signal in order to prevent the level of the digital output signal from exceeding a predetermined level. Attenuating means such as the digital input signal, the processed signal or the attenuated signal. , N times the sampling frequency of any one of the signal the input sampling frequency (N is 1
Sampling rate conversion means such as an oversampling unit for converting the sampling frequency into a larger (real number) sampling frequency;
Quantizing the generated attenuated signal,
Correcting the deterioration of the quantization characteristic caused when quantizing the attenuated signal corresponding to the frequency-level characteristic of the reduction processing in the attenuating means and the frequency-level characteristic in the signal processing, and correcting the quantization characteristic Performing a noise shaping process on the attenuated signal based on a noise shaping characteristic set in advance so as to shift an increase in quantization noise caused by a noise frequency band higher than a half of the input sampling frequency, Noise shaping means such as a noise shaping section for generating the digital output signal.

According to the operation of the invention described in claim 6, the signal processing means performs predetermined signal processing on the digital input signal to generate a processed signal.

The attenuating means generates an attenuated signal by reducing the level of the processed signal in response to the signal processing in order to prevent the level of the digital output signal from exceeding a predetermined level.

At this time, the sampling rate conversion means converts the sampling frequency of one of the digital input signal, the processed signal and the attenuated signal into a sampling frequency N times the input sampling frequency.

The noise shaping means quantizes the generated attenuated signal and quantizes the attenuated signal in accordance with the frequency-level characteristic of the reduction processing in the attenuating means and the frequency-level characteristic in the signal processing. Is set in advance so as to correct the deterioration of the quantization characteristics caused by the correction, and to shift the increase in the quantization noise caused by the correction of the quantization characteristics to a frequency band higher than a half of the input sampling frequency. A noise shaping process based on the noise shaping characteristics is performed on the attenuated signal to generate a digital output signal.

Accordingly, the sampling rate of any one of the digital input signal, the attenuated signal and the processed signal is increased, and the frequency-level characteristic of the reduction processing in the attenuating means and the signal processing in the attenuating means are performed on the attenuated signal. Since noise shaping processing corresponding to frequency-level characteristics is performed, even if reduction processing is performed by the attenuating means in order to adjust the level of the digital output signal, the bit component dropped out due to quantization of the reduced attenuated signal is compensated. And the quantization noise in a frequency band lower than one half of the input sampling frequency can be relatively reduced.

According to a seventh aspect of the present invention, there is provided a digital information processing apparatus as set forth in any one of the first to sixth aspects, wherein the signal processing means comprises the digital input signal. Is configured so that digital processing of a larger number of bits than the number of bits obtained by adding the number of bits reduced by each quantization to the number of bits in is possible.

According to the operation of the invention described in claim 7, in addition to the operation of the invention described in any one of claims 1 to 6, in addition to the above, the signal processing means may determine whether each bit in the digital input signal is Since the digital processing of the number of bits larger than the number of bits obtained by adding the number of bits reduced with the digitalization is possible, it is possible to prevent an increase in quantization noise due to so-called digit loss in the entire digital signal processing device.

According to another aspect of the present invention, there is provided a digital signal processing apparatus according to any one of claims 2 to 7, which outputs a sound corresponding to the digital output signal. Speaker means such as a loudspeaker, wherein the digital input signal is an audio signal sampled at the input sampling frequency higher than at least 40 Hertz, and the signal processing means comprises the audio signal. And the noise shaping means shifts the increase of the quantization noise to a frequency band higher than a half of the input sampling frequency to correspond to the acoustic signal. It is configured to generate a digital output signal.

According to the operation of the invention described in claim 8, in addition to the operation of the invention described in any one of claims 2 to 7, the speaker means outputs a sound corresponding to the digital output signal.

At this time, the digital input signal is an audio signal sampled at an input sampling frequency higher than at least 40 Hz.

The signal processing means generates a processing signal corresponding to the sound signal.

Further, the noise shaping means shifts the increase of the quantization noise to a frequency band higher than one half of the input sampling frequency to generate a digital output signal corresponding to the acoustic signal.

Therefore, it is possible to compensate for the dropped bit component due to the quantization of the processing signal corresponding to the sound signal whose level has been reduced, and to reduce the frequency band of the sound signal lower than half the input sampling frequency. The quantization noise can be relatively reduced.

According to a ninth aspect of the present invention, there is provided a loudspeaker system according to the eighth aspect, wherein a plurality of the loudspeaker means and a plurality of the loudspeaker means are provided for each of the loudspeaker means. Second attenuating means such as a plurality of attenuators for correcting output characteristics of the means, and the noise shaping provided for each of the loudspeaker means and also correcting deterioration of quantization characteristics caused by correction processing in the second attenuating means. A plurality of noise shaping means for respectively performing the noise shaping processing according to characteristics.

According to the operation of the ninth aspect of the invention, in addition to the operation of the eighth aspect of the invention, the second attenuating means provided for each of the plurality of loudspeaker means includes an output terminal for each of the loudspeaker means. Correct the characteristics.

The noise shaping means provided for each speaker means respectively performs the noise shaping processing by the noise shaping characteristic which also corrects the deterioration of the quantization characteristic caused by the correction processing in the second attenuation means.

Therefore, even in a speaker system having a plurality of speaker means, the quantization characteristics can be improved and the output characteristics of each speaker means can be corrected.

In order to solve the above-mentioned problems, a tenth aspect is provided.
According to the invention described in the above, in a speaker system including a speaker unit such as a speaker that outputs a sound corresponding to a digital input signal sampled at a preset input sampling frequency and input from the outside, the output characteristic of the speaker unit is A correcting means such as an attenuator for generating a correction signal by performing a correction process including at least a reduction process for reducing the level of the digital input signal on the digital input signal to correct the digital input signal; , The sampling frequency of one of the signals is set to N times (N
Is a real number greater than 1) and a sampling rate conversion means such as an oversampling unit for converting the generated correction signal into a sampling frequency, based on a noise shaping characteristic indicated by the setting signal. Noise shaping means, such as a noise shaping unit, which performs a noise shaping process to generate a digital output signal, and a quantization characteristic generated when the correction signal is quantized in accordance with the frequency-level characteristic of the correction process. The noise is corrected so as to correct the deterioration and shift the increase in quantization noise caused by the correction of the quantization characteristic to a frequency band higher than half the input sampling frequency to generate the digital output signal. A control unit that sets a shaping characteristic and generates the setting signal It includes a setting means, a.

According to the operation of the tenth aspect,
The correction unit performs a correction process including at least a reduction process for reducing the level of the digital input signal on the digital input signal in order to correct the output characteristic of the speaker unit, and generates a correction signal.

At this time, the sampling rate conversion means converts the sampling frequency of one of the digital input signal and the correction signal into a sampling frequency N times the input sampling frequency.

Then, the noise shaping means performs the noise shaping based on the noise shaping characteristic indicated by the setting signal.
The generated correction signal is quantized and subjected to noise shaping processing to generate a digital output signal.

At this time, the setting means corrects the deterioration of the quantization characteristic which occurs when the correction signal is quantized, and the quantization generated by the correction of the quantization characteristic in accordance with the frequency-level characteristic of the correction processing. A noise shaping characteristic is set so as to generate a digital output signal by shifting an increase in noise to a frequency band higher than a half frequency of the input sampling frequency, and a setting signal is generated.

Therefore, the sampling rate of any one of the digital input signal and the correction signal is increased, and the correction signal is subjected to noise shaping processing corresponding to the frequency-level characteristic of the correction processing. , The missing bit component can be compensated for by the quantization of the corrected signal, and the quantization noise in a frequency band lower than half the input sampling frequency can be relatively reduced.

In order to solve the above-mentioned problems, the present invention is directed to claim 11.
The invention according to claim 10, in the speaker system according to claim 10, wherein a plurality of the speaker means, and provided for each of the speaker means, for correcting output characteristics of the respective speaker means with respect to the digital input signal. And a plurality of correction means for respectively generating the correction signals, and provided for each of the speaker means, and also corrects the deterioration of the quantization characteristic caused by the correction processing in each of the correction means. A plurality of noise shaping means for respectively performing the noise shaping processing according to the noise shaping characteristics.

According to the operation of the eleventh aspect,
In addition to the effect of the invention according to claim 10, the correction means provided for each of the plurality of speaker means further performs a correction process for correcting the output characteristic of each of the speaker means on the digital input signal, A correction signal is generated respectively.

The noise shaping means provided for each speaker means respectively performs the noise shaping processing according to the noise shaping characteristic which also corrects the deterioration of the quantization characteristic caused by the correction processing in each correction means.

Therefore, even in a speaker system having a plurality of speaker means, the quantization characteristics can be improved and the output characteristics of each speaker means can be corrected.

In order to solve the above-mentioned problems, a twelfth aspect is provided.
According to the present invention, in the loudspeaker system according to the eleventh aspect, each of the correcting means is configured to compensate for a difference in output characteristics between the loudspeaker means.

According to the operation of the twelfth aspect,
In addition to the effect of the invention described in claim 11, each correction means compensates for a difference in output characteristics between the speaker means, so that a good sound without distortion can be output.

In order to solve the above-mentioned problems, a thirteenth aspect is provided.
According to the invention described in the above, in the speaker system according to any one of claims 8 to 12, among the digital output signals, the level of the digital output signal in a frequency band higher than one half of the input sampling frequency is set. The apparatus further includes low-pass filter means such as a low-pass filter for reduction.

According to the operation of the thirteenth aspect,
In addition to the effect of the invention described in any one of claims 8 to 12, the low-pass filter means may adjust the level of the digital output signal in a frequency band higher than one half of the input sampling frequency among the digital output signals. Reduce.

Therefore, it is possible to remove quantization noise that has shifted to a frequency band higher than the sampling frequency.

[0070]

Next, a preferred embodiment of the present invention will be described with reference to the drawings. The embodiment described below is an embodiment in which the present invention is applied to a speaker system having a plurality of speakers each of which plays a sound having a different frequency band.

(I) Principle of the Present Invention First, before describing a specific embodiment, the principle of the present invention will be described with reference to FIGS.

As shown in FIG. 1A, according to the present invention, an oversampling section 1 as a sampling rate converting means, an attenuating section 2 as an attenuating means,
It is composed of a signal processing unit 3 as a signal processing unit, a noise shaping unit 4 as a noise shaping unit, and a control unit 5 as a setting unit.

In this configuration, the type of the signal processing unit 3 may be either a fixed-point type or a floating-point type. In the following description, a case where a fixed-point type signal processing unit is used will be described. I do.

Further, the noise shaping section 4 has
As shown in (b), adders 6 and 9, an adder 7 as dither addition means, a requantizer 8, a filter 10
, And is constituted.

Next, the operation will be described.

The digital input signal Sin externally input to the oversampling unit 1 is oversampled by the oversampling unit 1 at a sampling frequency twice as high as the sampling frequency fs of the digital input signal Sin to generate a sampling signal Sov. The signal is output to the attenuator 2.

Next, the generated sampling signal Sov
Is based on a control signal Sca from the control unit 5, the signal processing unit 3 performs a level enhancement process (so-called boost process) on an attenuated signal Sat, which will be described later. The level of the sampling signal Sov is reduced so as not to exceed the maximum level that can be processed, and the attenuation signal Sat is generated and output to the signal processing unit 3.

The signal processing unit 3 performs a conversion process for converting the level of the input attenuated signal Sat based on the control signal Sr from the control unit 5.
A processing signal Spc is generated and output to the noise shaping unit 4.

Here, in the conversion processing in the signal processing unit 3, for example, the user can increase the level of the specific frequency band in the digital input signal Sin (the boost processing) or reduce the level of the specific frequency band. When an operation corresponding to the operation is performed by an operation unit (not shown), a control signal corresponding to the operation is input to the control unit 5, and the control unit 5 responds to the operation. The control signal Sr is output to the signal processing unit 3,
In the signal processing unit 3, the attenuation signal Sat
Is subjected to an enhancement process or a reduction process at a level corresponding to the operation.

Next, the noise shaping unit 4 performs a so-called noise shaping process on the input processing signal Spc based on the control signal Scn from the control unit 5,
A digital output signal Sout is generated and output to the outside.

Here, as the noise shaping processing, the attenuating section 2 based on the control signal Scn is used.
And re-quantizing the processed signal Spc whose level has been reduced in the signal processing unit 3 and correcting the lower bits deleted by the re-quantization, and increasing the so-called quantization noise caused by the correction. For the sampling frequency (currently 2 × fs) of the processing signal Spc, (fs
A process of shifting to a frequency band higher than the frequency of (/ 2) is executed.

More specifically, referring to FIG. 1B, the processing signal Spc input to the noise shaping processing unit 4 is a signal obtained by inverting the logic of the filter signal Sf from the filter 10 in the adder 6. Are added to generate an addition signal Sd.

Next, the addition signal Sd is added with a dither signal Sz by an adder 7 by a method described later, and is output to the requantizer 8 as an addition signal Sdz. Then, it is requantized in the requantizer 8 and output as the digital output signal Sout.

On the other hand, the digital output signal Sout is also output to the adder 9, where the added signal Sd is output.
Is added to a signal whose logic is inverted, and the result is input to the filter 10 as an addition signal Sad.

After that, the filter 10 performs a filtering process according to the noise shaping characteristic set based on the control signal Scn from the control unit 5, and outputs the filtered signal to the adder 6 as the filter signal Sf.

Here, the noise shaping process in the noise shaping section 4 will be described with reference to FIG.

In the following example, the sampling frequency of the digital input signal Sin is fs (accordingly,
The information as the digital input signal Sin has a frequency (fs
/ 2) It exists in the following frequency bands. This is based on the so-called sampling theorem. ), The digital input signal Sin is subjected to a 3 dB level enhancement process at the frequency f ₁ (<fs / 2) in the signal processing unit 3 and the frequency f ₂ (<fs / 2) as the center. This shows a case where a 6 dB level reduction process is performed. In response to this process, the attenuator unit 2 performs a 3 dB level reduction process on the sampling signal Sov uniformly over all frequency bands. ing.

First, in this example, the signal processing unit 3
As described above, since the level enhancement processing of 3 dB is performed around the frequency f ₁ and the level reduction processing of 6 dB is performed around the frequency f ₂ , the frequency-level characteristic is as shown in FIG. The characteristic has a change.

On the other hand, in response to the level enhancement processing in the signal processing section 3, the attenuating section 2 uniformly performs a 3 dB level reduction processing on the sampling signal Sov in all frequency bands. The characteristics are uniform as shown in FIG.

Then, the control unit 5 generates the control signal Scn so as to set the noise shaping characteristic as shown in FIG. 2B in the filter 10 corresponding to each processing in the signal processing unit 3. .

Here, the noise shaping characteristics shown in FIG. 2B need to satisfy the following three conditions from the principle.

(A) “1-H (z)” is the minimum phase transition characteristic.

(B) The average of the logarithmic power spectral density of “1-H (z)” is 0. That is,

(Equation 1) That.

(C) Filter 10 having M taps
In the case of, the following equation must hold.

[0095]

(Equation 2)

Therefore, the noise shaping characteristic shown in FIG. 2B is set as shown below after satisfying the above three requirements.

That is, for the frequency band of 0 ≦ f ≦ fs / 2,

H (z) = (frequency-level characteristic of signal processing unit 3) − (absolute value of noise increase due to addition of dither signal Sz + absolute value of level reduced in attenuating unit 2) A noise shaping characteristic curve shown in FIG. Here, the example shown in FIG. 2B shows a case where the noise is increased by 1 dB due to the addition of the dither signal Sz.

Next, in the frequency band of fs / 2 <f ≦ fs, the area of the area B indicated by the diagonally right-sloping line becomes equal to the area of the area A indicated by the diagonally right-sloping line in FIG. 2B. As described above, the point at which the characteristic curve intersects with the frequency axis in FIG. 2B and the maximum value level (the level indicated by reference symbol M in FIG. 2B) in the frequency band equal to or higher than the frequency of the intersection and equal to or lower than the frequency fs are defined as Set.

Note that the region indicated by the reference numeral B in FIG.
As long as the area of the area B is equal to that of the area B, the noise shaping characteristic of the area B may be any other characteristic as long as the above three conditions (a), (b) and (c) are satisfied.

Also, the frequency 2 × fs larger than the frequency fs
Noise shaping characteristics in the following frequency bands:
When the filter 10 is configured in the real number domain, FIG.
The frequency-level characteristic shown in (b) is folded line-symmetrically with a straight line parallel to the level axis (| 1-H (z) | axis) indicating the frequency fs as the axis of symmetry.

Then, as described above, the attenuation section 2
The noise shaping processing is performed in the noise shaping section 4 by the frequency-level characteristic shown in FIG. 2B set based on the level reduction processing and the signal processing in the signal processing section 3 to perform the above-described noise shaping processing. That is, while re-quantizing the processed signal Spc whose level has been reduced in the attenuating unit 2 and the signal processing unit 3 and correcting the lower bits deleted by the re-quantization, the so-called The increase of the quantization noise is determined by the processing signal Spc.
The function of shifting to a frequency band higher than the frequency of (fs / 2) for the sampling frequency of is exhibited.

Next, a method of adding the dither signal Sz in the adder 7 will be described with reference to FIG.

As shown in FIG. 3, the dither signal Sz in the adder 7 is, for example, as shown in FIG.
Although a dither signal Sz as shown in FIG. 2B is provided, the present invention is not limited to a dither generation method, an addition position thereof, a type of dither, and the like.

Next, in parallel with the operation of each component described above, the control unit 5 controls the signal processing unit 3 to perform the above-described control for level enhancement processing or level reduction processing based on an operation on an operation unit (not shown). The signal Sr is generated, and the reduction processing in the attenuating section 2 is performed so that the level does not exceed the maximum level that can be processed by the signal processing section 3 in accordance with the level of the enhancement processing to be performed in the signal processing section 3. The control signal Sca is generated to set the level of the attenuator 2 and output to the attenuator 2.

Further, based on the control signal from the operation unit, the control unit 5 responds to the levels of the enhancement processing and the reduction processing in the signal processing unit 3 and the level of the reduction processing to be performed by the attenuating unit 2 in FIG. The control signal Scn is output to the filter 10 in order to cause the noise shaping unit 4 to execute the noise shaping process having the characteristic shown in FIG.

The above components are controlled by the operation of the control unit 5.

(II) First Embodiment Next, a first embodiment of the present invention based on the above-described principle will be described with reference to FIGS. Note that the first embodiment described below is an embodiment in which the present invention is applied to a so-called two-way digital speaker system including two speakers.

In FIG. 4, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 4, the digital speaker system S of the first embodiment includes an oversampling unit 1 and an attenuating unit 2 having the above-described functions, a signal processing unit 3, and a noise shaping unit having the above-described functions. 4
a and 4b, D / A converters 36 and 44, and low-pass filters 37 and 4 as low-pass filter means.
5, amplifiers 38 and 46, and speakers 39 and 47 as speaker means. here,
The speaker 47 mainly reproduces high frequencies, and the speaker 39 mainly reproduces mid frequencies and low frequencies.

The signal processing unit 3 comprises a graphic equalizer 31, a low-pass filter 32, a high-pass filter 40, inverters 33 and 41, and attenuators 34 and 4 as second attenuating means and correcting means.
2, the delay units 35 and 43, and the control unit 5 having the above-described functions. Note that the maximum value of the number of bits that can be processed by the signal processing unit 3 is the number of bits (for example, 24 bits) in the digital input signal Sin, the number of bits that are reduced by re-quantization processing in each noise shaping unit described below. Number (eg 2 bits)
The digital processing of the number of bits equal to or more than the number of bits (for example, 26 bits) is enabled.

Further, the inverters 33 and 41 are respectively
Switches 33a, 33c, 41a and 41c and inverter 3
3b and 41b.

Here, the noise shaping units 4a and 4
b has the same configuration as the noise shaping unit 4 shown in FIG.

Next, the operation will be described.

The oversampling unit 1 generates a sampling signal Sov by oversampling the digital input signal Sin at a sampling frequency twice as high as the sampling frequency fs, and outputs the signal to the attenuation unit 2 in the same manner as described above.

The attenuator 2 performs the boost processing in the signal processor 3 based on the control signal Sca from the controller 5, and as a result, the level exceeds the maximum level that can be processed in the signal processor 3. The level of the sampling signal Sov is reduced so as not to cause the generation, and the attenuation signal Sat is generated and output to the signal processing unit 3. At this time, as the frequency-level characteristic in the level reduction processing, for example, a uniform level reduction characteristic over the entire frequency band shown in FIG.

Next, based on the control signal Sger from the control unit 5, the graphic equalizer 31 in the signal processing unit 3 performs a conversion process for increasing or decreasing the level of the input attenuated signal Sat. An equalizer signal Sge is generated and output to the low-pass filter 32 and the high-pass filter 40. At this time, as the frequency-level characteristic for the conversion process, for example, the characteristic shown as “signal processing unit” in FIG. 2A is adopted.

Next, the low-pass filter 32 extracts low-frequency and mid-frequency signals to be reproduced by the speaker 39 from the input equalizer signal Sge, and outputs the same to the inverter 33 as a low-frequency extraction signal Sl.

The inverter 33 is connected to the switch 33
a and 33c are operated cooperatively to invert the low-frequency extraction signal Sl by the inverter 33b or to pass the low-frequency extraction signal Sl as it is to generate the low-frequency inverter signal Slc and output it to the attenuator 34.

Here, the inverter 33 is connected to the speaker 39.
In some cases, the direction in which the diaphragm in the speaker 39 is vibrated is opposite to the same digital output signal Sout, which will be described later, so that the low-frequency extraction signal Sl is inverted as necessary to adjust this. It is to make it.

Next, the attenuator 34 reduces the level of the input low-frequency inverter signal Slc by a preset level based on the control signal Satl from the control unit 5 to generate a low-frequency attenuate signal Salc. And outputs it to the delay unit 35.

Here, the attenuator 34 is connected to the speaker 3
Depending on the type of the digital output signal 9, the output sound pressure level may be different even with the same digital output signal Sout,
This is for attenuating the level of the low-frequency inverter signal Slc as necessary to balance the sound pressure level output from the speaker 47 and correct distortion of the reproduced sound.

Next, the delay unit 35 adjusts the phase of the low-frequency attenuated signal Salc so as to match the phases of the sounds output between the speakers 39 and 47, respectively.
The low-frequency processing signal Spcl is generated and the noise shaping unit 4
output to a.

The noise shaping section 4a has low noise shaping characteristics corresponding to the level enhancement processing and the level reduction processing in the attenuator 2, the graphic equalizer 31, and the attenuator 34 based on the control signal Scnl from the controller 5a. The low-pass digital output signal Soutl is generated by performing noise shaping processing on the low-pass processing signal Spcl.

At this time, if the characteristic shown in FIG. 2A is adopted as the frequency-level characteristic of the level increasing processing and the level decreasing processing in the attenuating section 2 and the graphic equalizer 31, the noise shaping characteristic corresponds to the characteristic. As the frequency-level characteristic to be performed, for example, a characteristic in which the influence of the level reduction processing in the attenuator 34 is added to the frequency-level characteristic shown in FIG. 2B by a method similar to the method shown in FIG. 2 is adopted. You.

By this noise shaping processing, the lower-order bits deleted by the requantization of the low-frequency processed signal Spcl whose level has been reduced in the attenuator 2 and the signal processor 3 are corrected, and what is called by the correction is generated. The increase in quantization noise is equal to the original digital input signal S.
The frequency band is shifted to a frequency band higher than half the sampling frequency of in.

The D / A converter 36 converts the low-frequency digital output signal Soutl from a digital signal to an analog signal, generates a low-frequency analog signal Sla, and outputs it to the low-pass filter 37.

Next, the low-pass filter 37 reduces the signal in the frequency band equal to or higher than the frequency fs / 2 of the low-frequency analog signal Sla to generate an analog output signal Soual. Due to the function of the low-pass filter 37, most of the quantization noise generated in the processing of each section described above is shifted to the frequency fs / by the processing of the noise shaping section 4a.
Signals in two or more frequency bands are reduced, so that the quantization noise in a frequency band equal to or lower than the frequency fs / 2 is substantially reduced.

The amplifier 38 amplifies the analog output signal Soual to a level at which the speaker 39 can be driven.
The signal is output to the speaker 39 and driven.

Then, the speaker 39 outputs a sound corresponding to the analog output signal Soual.

On the other hand, the high-pass filter 40 extracts a high-frequency signal to be reproduced by the speaker 47 from the input equalizer signal Sge, and outputs it to the inverter 41 as a high-frequency extracted signal Sh.

The inverter 41 includes a switch 41
a and 41c are operated cooperatively to invert the high-frequency extraction signal Sh by the inverter 41b or pass it through as it is to generate the high-frequency inverter signal Shc and output it to the attenuator 42.

Here, similarly to the inverter 33, depending on the type of the loudspeaker 47, the direction of oscillating the diaphragm in the loudspeaker 47 may be opposite to the digital output signal South which will be described later. Therefore, the high-frequency extraction signal Sh is adjusted as necessary to adjust this.
Is for inverting.

Next, the attenuator 42 reduces the level of the input high-frequency inverter signal Shc by a preset level based on the control signal Sath from the control unit 5, and generates the high-frequency attenuate signal Sahc. And outputs it to the delay unit 43.

Here, as with the attenuator 34, the sound pressure level output from the attenuator 42 may be different even if the digital output signal South is the same depending on the type of the speaker 47. This is to attenuate the level of the high-frequency inverter signal Shc as necessary to balance the sound pressure level and correct the distortion of the reproduced sound.

Next, the delay unit 43 adjusts the phase of the high-frequency attenuated signal Sahc to match the phases of the sounds output between the speakers 47 and 39, respectively.
Generates high-frequency processed signal Spch and generates noise in shaping section 4
b.

Based on the control signal Scnh from the control unit 5, the noise shaping unit 4b has high noise shaping characteristics corresponding to the level enhancement processing and the level reduction processing in the attenuating unit 2, the graphic equalizer 31, and the attenuator 42. A noise shaping process is performed on the band processed signal Spch to generate a high band digital output signal South.

At this time, when the characteristic shown in FIG. 2A is adopted as the frequency-level characteristic of the level enhancement processing and the level reduction processing in the attenuating section 2 and the graphic equalizer 31, the noise shaping characteristic corresponds to that. As the frequency-level characteristic to be performed, for example, a characteristic in which the level reduction in the attenuator 42 is added to the frequency-level characteristic illustrated in FIG. 2B by a method similar to the method illustrated in FIG. 2 is adopted.

By this noise shaping processing, the lower bits deleted by the requantization of the high-band processing signal Spch whose level has been reduced in the attenuating section 2 and the signal processing section 3 are corrected, and a so-called correction generated by the correction is performed. The increase in quantization noise is equal to the original digital input signal S.
The frequency band is shifted to a frequency band higher than half the sampling frequency of in.

The D / A converter 44 converts the high-band digital output signal South from a digital signal to an analog signal, generates a high-band analog signal Sha, and outputs it to the low-pass filter 45.

Next, the low-pass filter 45 reduces a signal in a frequency band equal to or higher than the frequency fs / 2 of the high-frequency analog signal Sha, and generates an analog output signal Souah. Due to the function of the low-pass filter 45, most of the quantization noise generated by the above-described processing of each section is shifted to the frequency f by the processing of the noise shaping section 4b.
The signal in the frequency band equal to or higher than s / 2 is reduced, and thus the quantization noise in the audio frequency band is substantially reduced.

The amplifier 46 amplifies the analog output signal Souah to a level at which the speaker 47 can be driven.
The signal is output to the speaker 47 and driven.

Thereafter, the speaker 47 outputs a sound corresponding to the analog output signal Souah.

On the other hand, in parallel with the processing of each component for the low-frequency extraction signal Sl and the high-frequency extraction signal Sh described above, the control unit 5 adjusts the level corresponding to the level of the enhancement processing in the graphic equalizer 31. The control signal Sca is generated and output to the attenuator 2 so as to set the level of the reduction processing in the attenuator 2 so as not to exceed the maximum level that can be processed by the signal processor 3.

Further, the control unit 5 generates the control signal Sger corresponding to the level of the enhancement processing and the reduction processing to be executed in the graphic equalizer 31 in accordance with the operation of the operation unit (not shown). According to the level of the reduction processing, the level of the reduction processing performed by the attenuator unit 2 and the level of the reduction processing in the attenuators 34 and 42, for example, the noise shaping processing of the characteristic described above corresponding to the characteristic shown in FIG. The control signal Scnl is output to a filter in the noise shaping unit 4a so that the noise shaping unit 4a executes the control signal Scnh in the noise shaping unit 4b. Output to the filter.

Further, the control section 5 controls the control signals Satl and Sath to control the amount of reduction in the level of each of the attenuators 34 and 42 based on the balance between the preset sound pressure levels of the speakers 39 and 47, respectively. Is output.

As described above, according to the operation of the digital loudspeaker system S of the embodiment, the sampling rate of the digital input signal Sin is increased, and the attenuating section is applied to the high-frequency processing signal Spch or the low-frequency processing signal Spcl. 2 and a noise shaping process corresponding to the frequency-level characteristic of the reduction processing in the attenuator 34 or 42 and the frequency-level characteristic of the level enhancement processing and the reduction processing in the graphic equalizer 31 are performed, so that the frequency is one half of the sampling frequency fs. The quantization noise in the lower frequency band can be relatively reduced, and the high-band processing signal Spch or the low-band processing signal Spcl after the reduction processing in the attenuator 2 and the attenuator 34 or 42 and the reduction processing in the graphic equalizer 31 is requantized. That was dropped when Will be able to compensate for bets components can reproduce faithful sound more the digital input signal Sin without degrading the quantization characteristic in the original digital input signal Sin.

The noise shaping unit 4a or 4b
In, the quantization noise can be converted to white noise by the addition of the dither signal Sz, and the noise component increased by the addition of the dither signal Sz can also be removed.

Further, the signal processing unit 3 can perform digital processing of a larger number of bits than the sum of the number of bits in the digital input signal Sin and the number of bits reduced by the requantization processing in each noise shaping unit. Because of this, it is possible to prevent an increase in quantization noise due to so-called digit cancellation in the digital speaker system S as a whole.

In the above-described configuration, the low-pass filter 32 and the high-pass filter 40 have an equalizer signal S as shown in FIG.
The signal obtained by subtracting the high-frequency extraction signal Sh from the signal delayed by the delay unit 66 so as to compensate for the delay caused by the filtering process in the high-pass filter 40 may be output as the low-frequency extraction signal Sl. it can.

On the other hand, as shown in FIG. 5B, low-frequency extraction is performed from a signal obtained by delaying the equalizer signal Sge by the delay unit 68 so as to compensate for the delay caused by the filter processing in the low-pass filter 32. The signal obtained by subtracting the signal Sl may be output as the high-frequency extracted signal Sh.

(III) Second Embodiment Next, a second embodiment which is another embodiment of the present invention will be described with reference to FIG.

In the first embodiment described above, the case where the present invention is applied to the two-way digital speaker system S having only two speakers has been described. However, the second embodiment has a digital speaker system having more speakers. It is an embodiment about a speaker system.

As shown in FIG. 6, the digital speaker system S ′ according to the second embodiment includes the above-described oversampling unit 1, attenuating unit 2, graphic equalizer 31, low-pass filter 50, ,..., 52
, A high-pass filter 53, and speaker processing units 54, 5
5,..., 56, 57 and the low-pass filter 50,
, 52, and 52 and the high-pass filter 53, speakers 58, 59,..., 60, and 61 having different frequency bands of sounds to be reproduced from each other, and speaker processing units 54, 55,. , 56, 57, and a control unit 62 for controlling the attenuating unit 2 and the graphic equalizer 31 in an integrated manner.

Here, the speaker processing units 54, 55,...
.., 56, and 57 are an inverter (e.g., corresponding to the inverter 33), an attenuator (e.g., corresponding to the attenuator 34), and the like described in the first embodiment, respectively.
A delay unit (corresponding to, for example, the delay unit 35);
A noise shaping unit (e.g., corresponding to the noise shaping unit 4a), a D / A converter (e.g., a D / A
This corresponds to the A converter 36. ), A low-pass filter (corresponding to, for example, the low-pass filter 37) and an amplifier (corresponding to, for example, the amplifier 38).

Next, the operation will be described.

The oversampling unit 1, the attenuating unit 2, and the graphic equalizer 31 perform the same operations as in the first embodiment, and output an equalizer signal Sge.

.., 52, and a high-pass filter 53.
Extracts a signal corresponding to each pass frequency band from the equalizer signal Sge, and outputs the signals to the speaker processing units 54, 55,
..., 56 or 57.

Each of the speaker processing units 54, 55,...
, 56 or 57 perform the same processing as in the above-described first embodiment, and each speaker 58, 5
9,..., 60 and 61 are generated as analog output signals.

At this time, the control section 62 outputs the control signals Sca and Sger in accordance with the level change processing executed in the attenuator section 2, the graphic equalizer 31, and each attenuator, and also outputs the respective speaker processing sections 54 and 55. ,..., 56 and 57 are controlled by the respective speaker processing units 54, 55,.
Output to 56 and 57.

Thus, each of the output analog output signals is subjected to the noise shaping processing of the present invention by each noise shaping unit.

That is, in each analog output signal, the attenuation unit 2 and the graphic equalizer 31
In addition, the lower bits deleted by the requantization of each signal whose level has been reduced in each attenuator are corrected, and an increase in so-called quantization noise caused by the correction is added to the sampling frequency of the original digital input signal Sin. On the other hand, the frequency band is shifted to a frequency band higher than the frequency (fs / 2).

The speakers 58, 59,..., 60
And 61 reproduce the sound of the corresponding frequency band based on the corresponding analog output signal.

As described above, according to the digital speaker system S ′ of the second embodiment, in addition to the effects of the first embodiment, a plurality of speakers 58, 59,...
The speaker system S ′ having the speakers 58, 59,.
.., 60 and 61 can reduce the distortion of the reproduced sound and output a good sound.

(IV) Third Embodiment Next, a third embodiment which is still another embodiment of the present invention will be described with reference to FIG.

In the first or second embodiment described above, the case has been described where the graphic equalizer 31 performs not only the process of reducing the level of the attenuated signal Sat but also the process of increasing the level of the attenuated signal Sat. , Graphic equalizer 31 or attenuator 3
This is an embodiment in which the present invention is applied to a digital speaker system that performs only the level reduction processing of the attenuation signal Sat, the low-frequency inverter signal Slc, or the high-frequency inverter signal Shc in 4 or 42.

The configuration of the digital speaker system of the third embodiment is similar to that of the digital speaker system S shown in FIG.
Since this is basically the same as that of FIG.

Next, the setting of the noise shaping characteristics in the noise shaping unit, which is a feature of the third embodiment, will be described with reference to FIG.

In the graphic equalizer 31 of the digital speaker system according to the third embodiment, only the level reduction processing is performed as described above, so that the level of the signal handled by the processing of the graphic equalizer 31 itself is changed to the level of the graphic equalizer 31. It cannot exceed the maximum value of the level that can be handled by. Therefore, the third
In the embodiment, the level reduction processing in the attenuator unit 2 is not necessary.

Therefore, in the noise shaping processing of the third embodiment, the correction processing of the lower bits deleted by the requantization of each signal whose level has been reduced by the signal processing unit 3 and each attenuator and the so-called correction generated by the correction. A process of shifting the increase of the quantization noise to a frequency band higher than a half frequency of the sampling frequency is executed.

That is, the sampling frequency of the digital input signal Sin is fs, and the frequency f ₂ (<fs
/ 2) and a 6 dB level reduction process (that is, the graphic equalizer 31 and the attenuator 34).
Or the reduction process by a combination of 42) will be described more specifically while exemplifying with reference to FIG.
In this example, the signal processing section 3, since the only level reduction for 6 decibels around the frequency f _2, as described above, the frequency - level characteristics have changed as shown in FIG. 7 (a) Characteristics.

On the other hand, since the level reduction processing in the signal processing section 3 does not require the level reduction processing in the attenuating section 2, the frequency-level characteristics of the attenuating section 2 are uniform as shown in FIG. The characteristic is 0 dB.

Therefore, the noise shaping characteristics in the third embodiment are set as shown in FIG. 7B based on the three conditions shown in the first embodiment.

That is, for the frequency band of 0 ≦ f ≦ fs / 2,

H (z) = (frequency-level characteristic of signal processing unit 3) − (absolute value of noise increase due to addition of dither signal Sz + absolute value of level reduced in each attenuator) FIG. The curve of the noise shaping characteristic shown in b) is set. Here, the example shown in FIG. 7B shows a case where the noise is increased by 1 dB by the addition of the dither signal Sz.

Next, in the frequency band of fs / 2 <f ≦ fs, the area of the area B indicated by the diagonally right-sloping line becomes equal to the area of the area B indicated by the diagonally right-sloping line in FIG. 7B. As described above, the point at which the characteristic curve intersects with the frequency axis in FIG. 7B and the maximum value level (the level indicated by the symbol M in FIG. Set.

As in the first embodiment, FIG.
Is not limited to this characteristic. If the area of the area A is equal to the area of the area B, the noise shaping characteristic of the area B is determined by the above three conditions (a) and (b). ) And (c) may be any other characteristics as long as they are satisfied.

The frequency is larger than the frequency fs and the frequency is 2 × fs.
Noise shaping characteristics in the following frequency bands:
As in the first embodiment, the frequency-level characteristic shown in FIG. 7B is folded line-symmetrically with a straight line parallel to the level axis indicating the frequency fs as the symmetry axis.

As described above, FIG. 7 set based on the level reduction processing in the signal processing section 3
By performing the noise shaping process in the noise shaping unit according to the frequency-level characteristics shown in FIG. 2B, the function as the noise shaping process described above is exhibited.

As described above, according to the operation of the digital loudspeaker system of the third embodiment, the sampling rate of the digital input signal Sin is increased, and the signal processing unit 3 can cope with the frequency-level characteristic of the level reduction processing. Since the noise shaping process described above is performed, the bit components dropped by each requantization process can be compensated, and the quantization noise in a frequency band lower than a half frequency of the sampling frequency can be relatively reduced.

(V) Modifications Next, other modifications of the present invention will be described.

First, in each of the embodiments described above, the case where the level change in the graphic equalizer 31 is variable has been described. In addition to this, the level change in the graphic equalizer 31 is fixed only when the level change is set in advance. The present invention can also be applied to such a digital speaker system.

In this case, the degree of level reduction in the attenuator 2 is fixedly determined in accordance with the degree of level change in the graphic equalizer 31, so that the noise shaping characteristic in the noise shaping section is also variable. And the control unit in each of the above embodiments becomes unnecessary.

Also in this case, the noise-shaping characteristic is fixed by the above-described method corresponding to the frequency-level characteristic of the fixed graphic equalizer 31 and the frequency-level characteristic of the attenuator 2. Is determined, the effect as the present invention, that is, the quantization noise is reduced without lowering the quantization accuracy in the digital input signal Sin, the quantization characteristics are improved, and a sound closer to the digital input signal Sin is reproduced. can do.

In each of the above-described embodiments, the sampling rate in the oversampling unit 1 is first increased, but the position of the oversampling unit 1 is also different from the position before the noise shaping unit 4a or 4b. If so, it may be connected to any position.

Furthermore, if the signal processing unit 3 can handle a signal having a digital value of “1.0” or more by being constituted by, for example, a floating point type DSP, etc. 2 may be connected to any position different from the above embodiments.

More specifically, for example, the level of the digital output signal Sout is "1.0" as a digital value.
The attenuation unit 2 may be provided between the signal processing unit 3 and the noise shaping unit 4 so as not to exceed.

Further, in each of the above-described embodiments and modifications, the sampling frequency for the oversampling processing is twice the sampling frequency of the original digital input signal Sin. Even when the sampling frequency of the input signal Sin is converted to N times (N is a real number greater than 1), the same effects as those of each embodiment and modified embodiment can be obtained.

Further, in each of the above-described embodiments and modifications, the present invention relates to a digital input signal S as an audio signal.
Although the embodiment and the modified example when applied to in have been described, in addition to this, for example, the present invention is also applied to an image signal as it is, and a process involving an increase or decrease of the level is performed. It is possible to reduce quantization noise while maintaining quantization accuracy.

The noise shaping characteristics described so far have been set based on changes in the characteristics of the signal processing unit 3 or the attenuating unit 2. If the lower limit or the lower limit of the level change characteristic of the attenuator unit 2 is predetermined, the noise shaping characteristic can be fixedly determined based on the value.

Further, the above-described signal processing in the signal processing unit 3 and the attenuating unit 2 is executed for each sample. When these processes are executed in real time, the time of one sample is changed before the sampling frequency is changed. It is longer than after changing the sampling frequency.

Therefore, by placing the oversampling unit 1 after the signal processing unit 3 or the attenuating unit 2,
The time that can be used for performing the signal processing becomes longer. Thus, when the signal processing unit 3 having the same capability is used, if these processes such as level change are performed before the sampling frequency is changed, more processes are performed than if these processes are performed after the sampling frequency is changed. be able to.

[0191]

As described above, according to the first aspect of the present invention, the sampling rate of a digital input signal or a processed signal is increased, and the processed signal is adapted to the frequency-level characteristic of signal processing. Since the noise shaping process is performed, it is possible to compensate for bit components that are lost due to quantization of the processed signal whose level has been reduced, and to relatively reduce quantization noise in a frequency band lower than half the input sampling frequency. Can be effectively reduced.

Accordingly, signal processing can be performed while maintaining the accuracy of quantization of the original digital input signal, and quantization noise can be reduced and output, so that a digital output signal closer to the original digital input signal is obtained. be able to.

According to the second aspect of the present invention, the sampling rate of any one of the digital input signal, the attenuated signal and the processed signal is increased, and the attenuating means further reduces the processed signal by the attenuating means. The noise shaping process corresponding to the frequency-level characteristic of the frequency signal and the frequency-level characteristic of the increase / decrease signal processing is performed. Therefore, even when the signal processing unit performs the enhancement processing, the bit component dropped due to the quantization of the processing signal whose level has been reduced. Can be compensated for, and the quantization noise in a frequency band lower than half the input sampling frequency can be relatively reduced.

Therefore, even when the signal processing means performs the enhancement processing, it is possible to perform the signal processing while maintaining the quantization accuracy of the original digital input signal and reduce the quantization noise and output the original digital input signal. , A digital output signal closer to the digital input signal can be obtained.

According to the third aspect of the invention, the sampling rate of any one of the digital input signal, the attenuated signal and the processed signal is increased, and the attenuating signal is further reduced by the attenuating means. Since the noise shaping process corresponding to the frequency-level characteristic and the frequency-level characteristic in the increase / decrease signal processing is performed, even if the attenuation processing is performed by the attenuating means to adjust the level of the digital output signal, the attenuated signal whose level is reduced Can be compensated for the dropped bit component due to the quantization, and the quantization noise in the frequency band lower than half the input sampling frequency can be relatively reduced.

Therefore, even when the attenuation process is performed by the attenuating means, signal processing can be performed while maintaining the accuracy of quantization of the original digital input signal, and quantization noise can be reduced and output. A digital output signal closer to the digital input signal can be obtained.

According to the invention set forth in claim 4, claim 1 is provided.
In addition to the effects of the invention described in any one of Items 3 to 3, the quantization noise can be converted to white noise by adding dither, and the noise component increased by adding the dither can also be removed.

According to the fifth aspect of the present invention, the sampling rate of any one of the digital input signal, the attenuated signal and the processed signal is increased, and further, the attenuating means performs the reduction processing on the processed signal. Since the noise-shaping process corresponding to the frequency-level characteristic and the frequency-level characteristic of the signal processing in the signal processing means is performed, it is possible to compensate for the bit component which is dropped due to the quantization of the processing signal whose level is reduced, and
Quantization noise in a frequency band lower than one half of the input sampling frequency can be relatively reduced.

Therefore, signal processing can be performed while maintaining the quantization accuracy of the original digital input signal, and quantization noise can be reduced and output, so that a digital output signal closer to the original digital input signal is obtained. be able to.

According to the present invention, the sampling rate of any one of the digital input signal, the attenuated signal and the processed signal is increased, and the attenuating signal is further reduced by the attenuating means. Since the noise shaping process corresponding to the frequency-level characteristic of the signal processing and the frequency-level characteristic in the signal processing is performed, even if the attenuation processing is performed by the attenuating means to adjust the level of the digital output signal, the attenuation signal of the reduced level is It is possible to compensate for the bit components dropped by the quantization, and to relatively reduce quantization noise in a frequency band lower than one half of the input sampling frequency.

Therefore, even when the attenuation processing is performed by the attenuating means, signal processing can be performed while maintaining the quantization accuracy of the original digital input signal, and quantization noise can be reduced and output. A digital output signal closer to the digital input signal can be obtained.

According to the seventh aspect of the present invention, the first aspect
In addition to the effects of the invention described in any one of the above items 6, digital processing of a bit number greater than the number of bits obtained by adding the number of bits reduced with each quantization to the number of bits in the digital input signal is possible. Because of this, it is possible to prevent an increase in quantization noise due to so-called cancellation of digits in the entire digital signal processing device.

According to the invention described in claim 8, claim 2 is provided.
8. In addition to the effects of the invention described in any one of the above items 7, it is possible to compensate for missing bit components due to quantization of the processing signal corresponding to the reduced-level audio signal, and to perform input sampling in the audio signal. The quantization noise in a frequency band lower than one half of the frequency can be relatively reduced.

Therefore, signal processing can be performed while maintaining the quantization accuracy of the original audio signal, and quantization noise can be reduced to output a sound closer to the original digital input signal.

According to the ninth aspect of the present invention, the eighth aspect is provided.
In addition to the effects of the invention described in (1), even in a speaker system having a plurality of speaker units, the quantization characteristics can be improved and the output characteristics of each speaker unit can be corrected.

According to the tenth aspect, the sampling rate of any one of the digital input signal and the correction signal is increased, and the correction signal corresponds to the frequency-level characteristic of the correction processing. Since the noise shaping process is performed, it is possible to compensate for the bit component that has been dropped by the quantization of the corrected signal whose level has been reduced, and to relatively reduce the quantization noise in a frequency band lower than half the input sampling frequency. Can be effectively reduced.

Therefore, the output characteristics of the loudspeaker can be corrected while maintaining the accuracy of quantization in the original digital input signal, and the digital output signal can be output with reduced quantization noise. Sound closer to the digital input signal can be output from the speaker means.

According to the eleventh aspect of the present invention, in addition to the effect of the tenth aspect, even in a speaker system having a plurality of speaker means, the quantization characteristics are improved and each speaker means is improved. Can be corrected.

According to the twelfth aspect of the present invention, in addition to the effect of the eleventh aspect of the present invention, each correcting means compensates for a difference in output characteristics between the loudspeaker means. It can output sound.

According to the thirteenth aspect of the present invention, in addition to the effect of the eighth aspect of the present invention, the digital output signal has a frequency higher than one half of the input sampling frequency. Since the level of the digital output signal in the band is reduced, quantization noise that has shifted to a frequency band higher than one half of the input sampling frequency can be removed.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing the principle of the present invention, FIG. 1 (a) is a block diagram of an entire configuration, and FIG. 1 (b) is a block diagram showing a configuration of a noise shaping unit.

2A and 2B are diagrams illustrating a noise shaping characteristic of the present invention, wherein FIG. 2A is a diagram illustrating an example of a frequency-level characteristic of a signal processing unit and an attenuation unit, and FIG. 2B is a diagram illustrating an example of a noise shaping characteristic; FIG.

3A and 3B are diagrams illustrating dither addition, FIG. 3A is a diagram illustrating a first method of dither addition, and FIG. 3B is a diagram illustrating a second method of dither addition.

FIG. 4 is a block diagram illustrating a schematic configuration of the digital speaker system according to the first embodiment.

FIGS. 5A and 5B are block diagrams illustrating a configuration of a filter unit according to the first embodiment. FIG. 5A is a block diagram illustrating another configuration example, and FIG. 5B is a block diagram illustrating another configuration example. (II).

FIG. 6 is a block diagram illustrating a schematic configuration of a digital speaker system according to a second embodiment.

7A and 7B are diagrams illustrating noise shaping characteristics according to a third embodiment, in which FIG. 7A is a diagram illustrating an example of frequency-level characteristics of a signal processing unit and an attenuating unit, and FIG. 7B is an example of noise shaping characteristics; FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Over sampling part 2 ... Attenuation part 3 ... Signal processing part 4, 4a, 4b ... Noise shaping part 5 ... Control part 6, 7, 9, 65, 67 ... Adder 8 ... Requantizer 10 ... Filter 31 ... Graphic equalizers 32, 37, 45, 50 Low-pass filters 33, 41 Inverters 33a, 33c, 41a, 41c Switches 33b, 41b Inverters 34, 42 Attenuators 35, 43, 66, 68 Delay units 36, 44 ... D / A converters 38,46 ... Amplifiers 39,47,58,59,60,61 ... Speakers 40,53 ... High pass filters 51,52 ... Band pass filters 54,55,56,57 ... Speaker processing units S, S '... Digital speaker system D ... Data Z ... Dither Sin ... Digital input signal Sov ... Sampling Signal Sat ... attenuation signal Spc ... processing signal Sout ... digital output signal Sca, Scn, Scnl, Scnh, Sr, Sger, Satl, Sath
... control signals Sd, Sdz, Sad ... addition signal Sz ... dither signal Sf ... filter signal Sge ... equalizer signal Sl ... low-frequency extraction signal Slc ... low-frequency inverter signal Salc ... low-frequency attenuation signal Spcl ... low-frequency processing signal Soutl ... low Range digital output signal Sla ... Low range analog signal Soual, Souah ... Analog output signal Sout ... Digital output signal Sh ... High range extraction signal Shc ... High range inverter signal Sahc ... High range attenuation signal Spch ... High range processing signal South ... High range Digital output signal Sha: High frequency analog signal

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kiichiro Koguchi 4-2610 Hanazono, Tokorozawa-shi, Saitama Pioneer Corporation Inside the Tokorozawa Plant (72) Inventor Fumihiko Miyamoto 4-2610 Hanazono, Tokorozawa-shi, Saitama Pioneer Corporation Inside the Tokorozawa Plant (72) Inventor Izumi Nomura 4-2610 Hanazono, Tokorozawa City, Saitama Prefecture Inside the Tokorozawa Plant (72) Inventor Hayato Masunari 4-2610 Hanazono, Tokorozawa City, Saitama Prefecture Tokorozawa Plant Inside

Claims (13)

[Claims] 1. A digital input signal sampled at a preset input sampling frequency and input from the outside, at least including a reduction process for reducing a level of a preset specific frequency band in the digital input signal. A signal processing means for performing a predetermined signal processing to generate a processing signal; and setting the sampling frequency of one of the digital input signal and the processing signal to N times the input sampling frequency (N is 1 Sampling rate conversion means for converting the signal into a larger (real number) sampling frequency; and, based on the noise shaping characteristic indicated by the setting signal, quantizing the generated processing signal and performing noise shaping processing on the processing signal. Noise shaping to generate digital output signal Means for correcting the deterioration of the quantization characteristic caused when quantizing the processed signal in accordance with the frequency-level characteristic of the signal processing, and increasing the quantization noise caused by the correction of the quantization characteristic. Setting means for setting the noise shaping characteristic so as to generate the digital output signal by shifting to a frequency band higher than a half frequency of the input sampling frequency, and generating the setting signal. A digital signal processor characterized by the above-mentioned. 2. A digital input signal sampled at a preset input sampling frequency and input from the outside, the level of increase / decrease signal processing in a signal processing means for an attenuated signal is a level which can be processed by the signal processing means. Attenuating means for reducing the level of the digital input signal corresponding to the increase / decrease signal processing, generating the attenuated signal, and outputting the generated signal to the signal processing means, so as to prevent the signal from becoming higher; With respect to the attenuation signal, the level of a preset first specific frequency band is increased in the attenuated signal, and the level of a preset second specific frequency band different from the first specific frequency band in the attenuated signal is reduced. The increase including at least one of The signal processing means for performing the signal processing to generate the processed signal; and setting the sampling frequency of any one of the digital input signal, the attenuated signal and the processed signal to N (N is the input sampling frequency). Sampling rate conversion means for converting the sampling frequency into a (real number larger than 1) times sampling frequency; and, based on the noise shaping characteristic indicated by the setting signal, quantizing the generated processing signal and performing noise shaping processing on the processing signal. And noise shaping means for generating a digital output signal; and a quantum generated when the processing signal is quantized corresponding to the frequency-level characteristic of the reduction processing in the attenuating means and the frequency-level characteristic of the increase / decrease signal processing. The deterioration of the The noise shaping characteristic is set so as to generate the digital output signal by shifting an increase in quantization noise caused by the correction of the quantization characteristic to a frequency band higher than a half of the input sampling frequency, A digital signal processing device comprising: a setting unit configured to generate the setting signal. 3. An enhancement process for increasing a level of a preset first specific frequency band in a digital input signal sampled at a preset input sampling frequency and input from the outside, and Attenuating means for generating a processed signal by performing an increase / decrease signal process including at least one of a reduction process for reducing a level of a preset second specific frequency band different from the first specific frequency band in the attenuated signal; Signal processing means for outputting an attenuated signal corresponding to the increase / decrease signal processing so as to prevent the level of the digital output signal from exceeding a predetermined level. The attenuating means for outputting to the noise shaping means Sampling rate conversion means for converting the sampling frequency of any one of the input signal, the attenuated signal and the processed signal into a sampling frequency N (N is a real number greater than 1) times the input sampling frequency; Noise shaping means for quantizing the generated attenuated signal based on a noise shaping characteristic indicated by the signal and performing noise shaping processing on the attenuated signal to generate the digital output signal; and a reduction in the attenuating means. Corresponding to the frequency-level characteristic of the processing and the frequency-level characteristic in the increase / decrease signal processing, the deterioration of the quantization characteristic caused when quantizing the attenuated signal and the quantization caused by the correction of the quantization characteristic are corrected. The increase in noise Setting means for setting the noise shaping characteristic so as to generate the digital output signal by shifting to a frequency band higher than a half frequency of the input sampling frequency, and generating the setting signal. Digital signal processing device characterized by the following. 4. The digital signal processing device according to claim 1, wherein said noise shaping means further comprises dither adding means for adding a preset dither, and said setting means comprises: A digital signal processing apparatus, wherein the noise shaping characteristic is set so as to compensate for a noise component increased by the addition of the dither, and the set signal is generated. 5. A frequency-level characteristic set in advance corresponding to the signal processing in order to prevent the signal processing in the signal processing means for the attenuated signal from becoming higher than a level which can be processed by the signal processing means. Attenuating means for reducing the level of a digital input signal sampled at a preset input sampling frequency and input from the outside, and generating the attenuated signal, based on the generated attenuated signal, Based on the set frequency-level characteristic, a preset including at least one of an enhancement process for enhancing a level of a preset specific frequency band in the attenuated signal and a reduction process for reducing the level of the specific frequency band is set. The signal for performing the signal processing and generating a processed signal Sampling means for converting a sampling frequency of any one of the digital input signal, the attenuated signal and the processed signal into a sampling frequency N times (N is a real number greater than 1) the input sampling frequency. A rate conversion unit, when quantizing the generated processing signal, and quantizing the processing signal corresponding to the frequency-level characteristic of the reduction processing in the attenuating unit and the frequency-level characteristic in the signal processing. It is set in advance so as to correct the deterioration of the resulting quantization characteristic, and to shift the increase in the quantization noise caused by the correction of the quantization characteristic to a frequency band higher than one half of the input sampling frequency. Noise shaping processing based on noise shaping characteristics is performed on the processed signal. Te subjected, and noise shaping means for generating said digital output signal, digital signal processor, characterized in that it comprises a. 6. A reduction process for reducing a level of a predetermined specific frequency band in a digital input signal sampled at a predetermined input sampling frequency and input from the outside, and the characteristic. A signal processing means for performing a predetermined signal processing including at least one of an enhancement process for enhancing a frequency band level and generating a processed signal; and a level of a digital output signal exceeding a predetermined level. Attenuating means for reducing the level of the processed signal in response to the signal processing and generating an attenuated signal; and one of the digital input signal, the processed signal or the attenuated signal. The sampling frequency of the signal is N times the input sampling frequency (N is 1 A sampling rate converting means for converting the sampling frequency of large real number) Ri, together quantizes the attenuation signal said generated
Correcting the deterioration of the quantization characteristic caused when quantizing the attenuated signal corresponding to the frequency-level characteristic of the reduction processing in the attenuating means and the frequency-level characteristic in the signal processing, and correcting the quantization characteristic Performing a noise shaping process on the attenuated signal based on a noise shaping characteristic set in advance so as to shift an increase in quantization noise caused by a noise frequency band higher than a half of the input sampling frequency, And a noise shaping means for generating the digital output signal. 7. The digital information processing apparatus according to claim 1, wherein the signal processing unit reduces the number of bits in the digital input signal with the number of bits reduced with each quantization. A digital information processing device capable of performing digital processing of a larger number of bits than the number of bits added. 8. A speaker system comprising: the digital signal processing device according to claim 2; and speaker means for outputting a sound corresponding to the digital output signal. The signal is an audio signal sampled at the input sampling frequency higher than at least 40 Hz, the signal processing means generates the processed signal corresponding to the audio signal, and the noise shaping means further comprises the quantization A speaker system for generating the digital output signal corresponding to the acoustic signal by shifting an increase in noise to a frequency band higher than a half frequency of the input sampling frequency. 9. The loudspeaker system according to claim 8, wherein a plurality of said loudspeaker means, a plurality of second attenuator means provided for each of said loudspeaker means and for correcting output characteristics of said loudspeaker means, A plurality of noise shaping means provided for each of the speaker means, each of which performs the noise shaping processing with the noise shaping characteristic that also corrects the deterioration of the quantization characteristic caused by the correction processing in the second attenuating means. A speaker system comprising: 10. A loudspeaker system comprising speaker means for outputting a sound corresponding to a digital input signal which is sampled at a preset input sampling frequency and inputted from the outside, wherein a digital signal is output to correct an output characteristic of said speaker means. A correction unit that performs at least a reduction process for reducing the level of the digital input signal on the input signal to generate a correction signal; and the digital input signal or the correction signal of one of the correction signals. Sampling rate conversion means for converting the sampling frequency to a sampling frequency N times the input sampling frequency (N is a real number greater than 1); and quantizing the generated correction signal based on a noise shaping characteristic indicated by a setting signal. And at the same time, A noise shaping unit that performs a noise shaping process to generate a digital output signal; and, in accordance with a frequency-level characteristic of the correction process, corrects deterioration of a quantization characteristic that occurs when the correction signal is quantized, and The noise shaping characteristic is set so as to generate the digital output signal by shifting an increase in quantization noise caused by the correction of the quantization characteristic to a frequency band higher than a half of the input sampling frequency, A speaker system comprising: a setting unit configured to generate the setting signal. 11. The loudspeaker system according to claim 10, wherein a plurality of said loudspeaker means are provided for each of said loudspeaker means for correcting output characteristics of said loudspeaker means with respect to said digital input signal. A plurality of the correction means for further performing the correction processing and respectively generating the correction signal; and a plurality of correction means provided for each of the speaker means for correcting deterioration of a quantization characteristic caused by the correction processing in each of the correction means. And a plurality of noise shaping units each of which performs the noise shaping processing according to a noise shaping characteristic. 12. The speaker system according to claim 11, wherein each of said correcting means compensates for a difference in output characteristics between each of said speaker means. 13. The speaker system according to claim 8, wherein a level of the digital output signal in a frequency band higher than one half of the input sampling frequency is reduced among the digital output signals. A speaker system, further comprising a low-pass filter unit that performs the operation.