JPH0445005B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a circuit for adjusting gain in a circuit that digitizes analog input, processes the signal, converts it back to analog, and outputs the signal. This reduces the effects of [Background of the Invention] Conventional gain adjustment circuits for audio control amplifiers and the like generally process analog inputs as they are and output the analog signals. However, if the signal processing is performed digitally, it is advantageous because control characteristics can be freely applied. As a gain adjustment circuit configuration for digitizing an analog signal and performing signal processing, for example, the configuration shown in FIG. 17 or FIG. 18 can be considered. In the example shown in FIG. 17, an analog input is processed into a digital signal by a digital processing circuit 1 and then returned to an analog signal, and the gain is adjusted by a variable gain circuit 2. The digital processing circuit 1 is
The analog input is converted into a digital signal by the A/D conversion circuit 3, and the digital processing section 4 performs digital signal processing such as tone control.
A conversion circuit 5 converts it into an analog signal. Further, the variable gain circuit 2 includes an analog amplifier 2a and an analog attenuator 2b. analog amplifier 2a
gives the rated gain G of the entire gain adjustment circuit, and in the case of audio control amplifiers, the gain is generally set to +20 dB.
The analog attenuator 2b is used to adjust the gain, and generally the amount of attenuation is varied in the range of 0 to -∞dB, and the overall gain of the entire gain adjustment circuit is adjusted in the range of G to -∞dB. do. In the circuit shown in FIG. 18, contrary to the circuit shown in FIG. 17, the gain of the analog input is adjusted by the variable gain circuit 2, and then the digital signal processing circuit 1 performs digital signal processing. [Problems to be Solved by the Invention] In the digital processing circuit 1, error noise and quantization noise occur, and the noise level becomes constant at a value determined by the number of processing bits. The configuration shown in FIG. 17 has the disadvantage that the noise level at the output increases because the analog amplifier 2a amplifies the noise generated in the digital processing circuit 1 when the total gain is 0 dB or more. Furthermore, in the configuration shown in FIG. 18, when the overall gain is reduced, the signal level input to the digital processing circuit 1 is narrowed down and becomes smaller, but the noise level generated in the digital processing circuit 1 does not change, so the output The proportion of noise inside increases and S/
N gets worse. This invention was made in view of the above points, and attempts to prevent an increase in noise level and deterioration of S/N in a gain adjustment circuit that processes an analog input into a digital signal, adjusts the gain, and outputs it. It is something. [Means for Solving the Problems] The present invention includes an analog amplifier and a first analog attenuator into which an analog signal is input, and an A/D converter for the outputs of the analog amplifier and the first analog attenuator. a digital signal processing circuit that processes the signal and then D/A converts it to output; a second analog attenuator that inputs the output of this digital processing circuit; The total gain in signal level transmission between the output of the analog attenuator 2 and the output of the analog attenuator 2 is defined as the gain 1
a gain adjustment operator that instructs an arbitrary value between a larger rated gain and a maximum attenuation gain that is extremely smaller than a gain of 1, and a total gain that the gain adjustment operator instructs is between the rated gain and the gain of 1; , the gain of the second analog attenuator is set to approximately 1, and the gain of the analog amplifier and between the input of the first analog attenuator and the output of the second analog attenuator is set to approximately 1. performing gain distribution to set the amount of attenuation of the first analog attenuator so that the total gain in audio signal level transmission matches the total gain instructed by the gain adjustment operator; If the overall gain is between a gain of 1 and the maximum attenuation gain, the first analog attenuation gain is adjusted such that the total gain of the gain of the analog amplifier and the gain of the first analog attenuator is approximately 1. While setting the attenuator gain,
so that the total gain in audio signal level transmission between the input of the analog amplifier and the first analog attenuator and the output of the second analog attenuator matches the total gain instructed by the gain adjustment operator. and gain adjustment control means for performing gain distribution to set the amount of attenuation of the second analog attenuator. [Operation] According to the present invention, the gain adjustment of the total gain based on the instruction from the gain adjustment operator is performed separately before and after digital signal processing. In other words, the first analog attenuator at the front stage of digital signal processing performs gain adjustment in a range where the total gain is larger than the gain of approximately 1 (0 dB), and the second analog attenuator at the rear stage performs gain adjustment within a range where the total gain is approximately greater than the gain of 1. It also performs gain adjustment over a small range. According to this, when the total gain is set to a range that is approximately larger than a gain of 1, the gain is increased in the first stage of digital signal processing, the gain is approximately 1 in the subsequent stage, and the total gain is set to a range that is approximately smaller than a gain of 1. In this case, the gain is approximately 1 in the first stage of digital signal processing, and attenuation is performed in the second stage of analog signal processing. Therefore, even if the overall gain is reduced, the signal level at the stage before digital signal processing will not drop below approximately 0 dB, so the digital processing circuit will operate at nearly full bits, and the S/N ratio here will be reduced.
The deterioration is almost negligible. Further, since the noise in the digital processing circuit is narrowed down at the subsequent stage, the noise level itself becomes smaller. Furthermore, even if the total gain is increased, the gain will increase in the stage before the digital processing circuit, and the deterioration of S/N here will still be kept to a minimum.Furthermore, since the analog stage after the digital processing circuit has a gain of almost 1, Noise generated in the digital processing circuit is not amplified. [Examples] Examples of the present invention will be described below. FIG. 1 shows the basic configuration of this invention. After adjusting the gain in the variable gain circuit 6, the analog input is input to the digital processing circuit 1, where it is digitally processed, and then sent to the analog attenuator 7.
Output via . The variable gain circuit 6 includes an analog amplifier 6a and an analog attenuator 6b (first analog attenuator). The analog amplifier 6a gives the rated gain G of this gain adjustment circuit, and in the case of an audio control amplifier, it is generally +
The gain is set to 20dB. The analog attenuator 6b adjusts the gain of the previous stage, and varies the amount of attenuation within the range of 0 to -GdB, thereby adjusting the overall gain of the entire gain adjustment circuit within the range of G to 0 dB. The digital processing circuit 1 converts the analog input into A/
The D conversion circuit 3 converts it into a digital signal, the digital processing section 4 performs digital signal processing such as filtering, and the D/A conversion circuit 5 converts it into an analog signal. Analog attenuator 7 (second analog attenuator) is used to adjust the gain of the subsequent stage, and is
The amount of attenuation is varied in the range of ~-∞dB. The gain control circuit 8 (gain adjustment control means) controls the amount of attenuation of the attenuator 6b and the attenuator 7, and controls the overall gain of the entire circuit to be set (set by the gain adjustment operator 9 such as a master volume). ), control as follows. When setting the overall gain in the range of G (rated gain) to 0 dB (gain 1), the attenuator 7 is set almost through (0 dB), and the attenuator 6b is controlled in the range of 0 to -GdB.
As a result, the gain of the variable gain circuit 6 is controlled within the range of G to 0 dB, and the overall gain is increased here.
At this time, since the attenuator 7 is almost through, the noise generated in the digital processing circuit 1 is not amplified. When setting the overall gain in the range of 0 (gain 1) to -∞dB (maximum attenuation gain), the combined gain of analog amplifier 6a and attenuator 6b is set to almost through (0 dB), and attenuator 7 is set in the range of 0 to -∞dB. Attenuation is performed by an attenuator 7. At this time, the combined gain of the analog amplifier 6a and attenuator 6b is almost through, so the digital processing circuit 1 has almost no gain.
A signal is input without attenuation at 0 dB, and this digital processing circuit 1 is close to full-bit operation, and even if error noise, quantization noise, etc. occur, the S/N is low.
deterioration becomes negligible. Furthermore, since these noises are narrowed down by the attenuator 7 at the subsequent stage, the noise level itself becomes smaller. Next, an embodiment in which the present invention is applied to an audio control amplifier will be described. In this embodiment, as shown in FIG. 10, which will be described later, the analog input is passed through the VCA 26 to a digital processing circuit consisting of an A/D conversion circuit 40, a digital equalizer 42 (digital processing section), and a D/A conversion circuit 46. input and its analog output signal
Digital loop 1 output via VCA32
4, and the present invention is applied to this route. In other words, VCA26 (has the functions of an analog amplifier and a first analog attenuator).
is the rated gain D (=+
20dB) to 0dB, VCA32
(which has the function of a second analog attenuator) varies the gain in the range of 0 to -∞dB. And when the total gain is in the range of G to 0dB, VCA32
is fixed at 0 dB, and the gain is controlled by the VCA 26. Also, when the total gain is in the range of 0 to -∞dB,
VCA 26 is fixed at 0 dB, and VCA 32 controls the amount of attenuation. This example will be explained in detail below. First, an outline of this control amplifier is shown in Figure 2. This control amplifier uses a path (analog straight path 12,
A sound field effect signal is sent to three channels (digital loop 14, digital straight path 18) and four channels of sound field effect speakers c, d, e, f (c, d can be substituted for main speakers a, b). , and a video signal path 24 for supplying a video signal to a television monitor g placed in the center of the main speakers a and b. Each route will be explained. Analog straight path 12 This is a path that amplifies the signal of the analog source 10 and outputs it as it is (two channels, left and right). This is used when tone control or the like is not performed on the signal of the analog source 10. The signal of the analog source 10 is input from the input terminal 11, and the VCA 26 and the output selection circuit 28 (select whether to output from the analog straight path 12 or the digital path 15 (digital loop 14 or digital straight path 18)) mode. The signal is led to the main signal output terminal 36 via a selection circuit (selecting stereo output or monaural output) 30, VCA 32, and buffer amplifier 34. Main signal output terminal 36 (2 channels left and right)
are connected to the power amplifier's main signal left and right input terminals. Note that the analog source 10 is led to the analog recording output terminal 38 as a recording source signal. Digital loop 14 This is a path that once converts the signal from the analog source 10 into a digital signal, performs digital signal processing such as tone control, and then returns it to an analog signal and outputs it. This is used when performing tone control or the like on the signal of the analog source 10. The signal from the analog source 10 is converted into a digital signal via the VCA 26 by an A/D conversion circuit 40 with a built-in dither circuit, and then input to a digital equalizer 42 . Digital equalizer 42
is a digital equalizer processor, which is composed of a three-band parametric equalizer with bandpass characteristics, and can arbitrarily set the center frequency, Q, and level for each divided band. Furthermore, the cutoff frequencies of the low cut and high cut and the gradients (attenuation rates) of their slopes can be set arbitrarily. The tone-controlled output of the digital equalizer 42 is output to the main signal output terminal 36 via a 4x oversampling digital filter 44, a D/A conversion circuit 46, an output selection circuit 28, a mode selection circuit 30, a VCA 32, and a buffer amplifier 34. Ru. Digital straight path 18 This is a path for inputting the signal from the digital source 16 from the input terminal 17, processing the digital signal, converting it into an analog signal, and outputting the signal. The digital source 16 signal is input to a digital I/O receiver 48 . The digital I/O receiver 48 is a circuit that interfaces the input signal of the digital source 16 with subsequent circuits. This digital I/O receiver 48 has an internal PLL circuit, and uses the sampling frequency of the digital source 16 (for example, 44.1kHz for a CD (compact disk), 48k for a DAT (digital audio tape recorder)).
Hz), and detects the presence or absence of digital source 16 and the presence or absence of errors (parity check).
Outputs subcode, etc. Note that if both analog and digital signals are input from the same input source (for example,
CD, DAT, VDP), digital I/
The O receiver 48 automatically selects the high quality digital source 16 and outputs the digital equalizer 4.
2, and the digital loop 14 of the analog source 10 is cut off. This allows the input source to
Even if the characteristics of the digital processing circuit (D/A converter, etc.) in the CD or DAT are poor, the high-precision digital processing circuit in this control amplifier can be used without using it, resulting in a high-quality analog final output. can be obtained. The digital signal received by the digital I/O receiver 48 is transmitted to a digital volume 49,
Digital equalizer 42, 4x oversampling digital filter 44, D/A conversion circuit 4
6, output selection circuit 28, mode selection circuit 30,
The signal is led to the main signal output terminal 36 via the VCA 32 and buffer amplifier 34. Note that the signal of the digital source 16 is guided to the digital recording output terminal 50 as a recording source signal. To summarize the above, three types of main signal paths 1
2, 14, and 18 can be used as follows.

[Table] Sound field effect path 22 This path inputs a digitized source to the sound field processor 20 to create a sound field sound effect, converts it into an analog signal, and outputs it. This sound field effect, as shown in Figure 3 above,
An impulse signal is emitted on an actual stage such as a hall, church, or studio, and the many early reflections arriving at the listening point from all directions are captured by 4-point (i.e., 4-channel) microphones placed at the listener's seat, and the data is then used. Through digital processing, a virtual sound source distribution is stored for each direction of arrival (for example, 22 pieces per speaker, for a total of 88 pieces of early reflection sound data), and this is recalled during playback.
A source signal is added to this to reproduce a sound field similar to the measured sound field. The sound field processor 20 processes 16 factory programs preset as early reflection sound information for sound field effects and stored in memory, and 16 user programs created by the user by changing the parameters of the factory programs. Based on one program selected by the user, a sound field sound effect is created by performing a convolution operation with the output of the digital equalizer 42, (time division processing) is outputted to sound field sound effect output terminals 60, 62 via 4x oversampling digital filters 52, 54 and D/A conversion circuits 56, 58 with digital volume. The sound field effect output terminals 60 and 62 are connected to the sound field effect input terminal (4 channels) of the power amplifier. This sound field effect path 22 is kept alive even when the digital equalizer 4 is turned off (a sound field effect signal is generated by inputting a signal with a flat characteristic). Video signal path 24 Inputs the signal of the video source 60 from the input terminal 61 and directly outputs it to the video recording output 62 or monitor output 64
It is a route that leads to. Here, FIG. 10 shows the gain distribution for volume adjustment in the control amplifier of FIG. 2. Each route will be explained. (1) Analog straight path 12, digital loop 14, VCA26+VCA32 is the total gain between input and output. The VCA 26 has a maximum gain of +20 dB as the rated gain G of these paths 12 and 14,
It is attenuated in the range of +20 to 0dB. The VCA 32 has a maximum gain of 0 dB and is attenuated in the range of 0 to -∞ dB. As shown in FIG. 11, the VCAs 26 and 32 are
When the total gain ranges from +20dB (maximum volume) to 0dB (gain 1 between input and output), VCA26 works,
VCA32 becomes through (gain 1). Also, in the range of total gain from 0dB to -∞dB, VCA26
is passed through and VCA32 works. Therefore,
In the digital loop 14, as shown in FIG. 12, when the volume is set high (total gain +20 to 0 dB), the A/D conversion circuit 40 and the D/A conversion circuit 46 have no gain at the subsequent stage (no gain 1), these residual noises (A/D quantization noise and D/A error noise) do not increase. Also, when the volume is set low (total gain 0
-∞dB) is the digital processing circuit (A/D conversion circuit 40, digital equalizer 42, D/A
Since a signal is inputted to the conversion circuit 46) with a gain of 1, the S/N ratio will not deteriorate even if residual noise occurs in this digital processing circuit. Furthermore, since attenuation is performed at the subsequent stage of the digital processing circuit, the residual noise level itself is attenuated and output. (2) Digital straight path 18 Digital volume 49 + VCA 32 becomes the total gain between input and output. The digital volume 49 has a maximum gain + as the rated gain G of this path 18.
It has a gain of 20dB and is attenuated from +20 to 0dB. As mentioned above, VCA32 has a maximum gain of 0dB,
It is attenuated in the range of 0 to -∞dB. Digital volume 49 and VCA 32 are the first
As shown in Fig. 1, when the overall gain is in the range of +20 dB (maximum volume) to 0 dB (input/output gain 1), the digital volume 49 works and the VCA 32 becomes through (gain 1). Further, when the total gain is in the range of 0 dB to -∞ dB, the digital volume 49 has a gain of 1, and the VCA 32 is activated. Therefore, in the digital straight path 18, as shown in number 12, when the volume is set high (total gain +20 to 0 dB), there is no gain at the downstream stage of the digital equalizer 42 or the D/A conversion circuit 46 ( Since the gain is 1), their residual noise (D/A error noise) does not increase. Also, when the volume is set low (total gain 0
~-∞dB), the signal is input to the digital equalizer 42 and the D/A conversion circuit 46 at 0 dB, so even if residual noise occurs in these circuits 42 and 46, the S/N ratio will not deteriorate. Furthermore, since attenuation is performed at the subsequent stage of these circuits 42 and 46, the residual noise level itself is attenuated and output. (3) Sound field effect path 22 In the case of analog source 10, VCA26+
The digital volume in the D/A 56, 58, or in the case of the digital source 16, the digital volume 49+the digital volume in the D/A 56, 58, respectively, becomes the total gain between input and output.
The VCA 26 or the digital volume 49 has a maximum gain of +20 dB as the rated gain G of this path 22, and is attenuated in the range of +20 to 0 dB. In the D/A conversion circuits 56 and 58, the digital volume is attenuated in the range of 0 to -∞dB with a maximum gain of 0 dB. The VCA 26 or digital volume 49 and the digital volume in the D/A 56, 58 are:
As shown in Figure 11, in the range from total gain +20 dB (maximum volume) to 0 dB (gain between input and output 1),
VCA26 or digital volume 49 works,
The digital volume in the D/A conversion circuits 56 and 58 becomes through (gain 1). Also, the total gain is
In the range from 0 dB to -∞ dB, the VCA 26 or the digital volume 49 is turned on, and the digital volume in the D/A conversion circuits 56 and 58 works. The total gain of each path includes the main volume, left/right balance volume, audio output, and impression level adjustment (hereinafter referred to as main,
Main signal muting (effects only on the main signal), sound field effect signal muting, balance before and after sound field effects, sound field effect signal level (effects only on sound field effect signals), etc. The amount of adjustment of the volume adjustment operation means (the details of each will be described later) is determined by a microcomputer by making a comprehensive judgment. Then, the microcomputer determines the gain distribution of each volume adjusting means (VCA 26, 32, digital volume 49, D/A conversion circuit 56, 58) and controls each gain so that the total gain is obtained. Next, details of the control amplifier shown in FIG. 2 explained above will be explained. FIG. 4 shows the front panel of the control amplifier shown in FIG. 2. Each part will be explained. (1) Power switch 70 This control amplifier power switch turns on the LED (light emitting diode) indicator 7.
2 lights up. When the power switch 70 is turned on, each part of this control amplifier returns to the setting state before the power was turned off. (2) Operation lock on/off key 73 This key enables or disables parameter setting operations for the digital equalizer and sound field processor using front panel keys. When turned on, it becomes an operation lock.
Parameter setting operations become impossible (however, parameter setting operations using the remote control are accepted).
This can prevent setting values from being changed by a child or the like mischievously operating the keys on the panel while the user is using the remote control. Also, when turned off, the lock is released and parameters can be set using the front panel (operations using the remote control are also possible). (3) Input selector 74 This selector selects the input source connected to this control amplifier, and includes selector keys 74-1 to 74-11 consisting of tact switches. By pressing each selector key 74-1 to 74-11, the next input source is selected respectively. 74-1: Compact disk player (CD) 74-2: Digital audio tape recorder 1 (DAT1) 74-3: Digital audio tape recorder 2 (DAT2) 74-4: Record player (PHONO
AMP) 74-5: TUNER 74-6: Analog audio tape recorder 1 (TAPE1) 74-7: Analog audio tape recorder 2 (TAPE2) 74-8: Video disc player 1 (VDP1) 74-9: Video Disk player 2 (VDP2) 74-10: Video tape recorder 1 (VTR1) 74-11: Video tape recorder 2 (VTR2) Each input selector key 74-1 to 74-
11 has LED indicators 76-1 to 74-
11 are provided adjacent to each other, and the selected input source lights up in green. Also, here, if the selected input source signal is digital,
LED indicator 78 lights up to indicate that the digital input is selected. (4) Record out key 80 Transfers the input source signal to each recording device (DAT1, DAT2,
This key outputs the recording source signal to TAPE1, TAPE2, VCR1, VCR2). This key 80
When turned on, the LED indicator 82 flashes for 5 seconds. Each operation mode described below is set by the operation during this 5 seconds. (a) If you operate the input selector 74 while the LED indicator 82 is blinking, the signal of the input source corresponding to the pressed key will be supplied to each recording device (however, the input source itself ). Therefore,
If you perform a recording operation on the recording device side, the signal from this input source will be recorded. Furthermore, at this time
Of the LED indicators 76-1 to 76-11, the input source selected by the input selector 74 lights up in red (the LED indicators 76-1 to 76-11 have two green and red lights).
Consists of colored LEDs. ) indicates that the signal from that input source is being output as the recording source signal. Note that the input source used for playback, such as a normal speaker, and the input source used as a recording signal can be selected independently, so that while enjoying music from one input source, the signal from another input source can be connected to the recording device. can be recorded. (b) Without operating the input selector key 74,
When the record out key 80 is pressed again, the output of the recording source signal is stopped and no longer supplied to any recording device. LED indicator 7
The red lights of 6-1 to 76-11 are also turned off. (c) Within 5 seconds while the record out LED indicator 82 is flashing, press the input selector 7.
4. If none of the record out keys 80 is operated, the input source that was last selected as the recording source signal is supplied to each recording device again, and one of the LED indicators 76-1 to 76-11 The corresponding one lights up in red. This simplifies the recording source signal selection operation by allowing you to select the signal from the same input source as the previous one without having to operate the input selector 74 each time. . (5) Mode key 84 This is used to select whether to output the main signal in stereo or monaural. When monaural is selected, the LED indicator 86 lights up. (6) Input level setting key 88 Since the source signal level differs depending on the input source, by adjusting the mutual volume ratio in advance on the control amplifier side, even if the input source is changed, the volume by the master volume can be adjusted. This eliminates the need to make adjustments. The input level setting key 88 is comprised of a seesaw type switch. When an input source is selected with the input selector 74, pressing the left side of the input level setting key 88 will increase the volume, and pressing the right side will decrease the volume. The volume changes in 0.2 dB steps in the range of 0 to -6 dB with 0 dB as the initial value. At this time, 16 rows 2
As shown in Figure 5, the line LCD (liquid crystal display) 90 displays the fact that input level setting is being performed, the name of the input source being set, and the level setting value. stored in memory in real time. This setting value is retained even if the power switch 70 is turned off.
When the input level setting key 88 is released, the input level setting mode is canceled 5 seconds later. When an input source is selected with the input selector 74, the input level set for that input source is read out, and each volume adjustment means (VCA 26, 32 in FIG. 2, digital volume 4)
9, the digital volume in the D/A conversion circuits 56 and 58) are controlled to set the offset of the main volume 94 and correct variations in source signal level for each input source. As a result, even if the input source is switched using the input selector 74, the volume can be made the same for each input source without adjusting the main volume 94. (7) Muting key 92 This is an audio muting key that attenuates the volume by -20 dB. With muting on, LED indicator 9
3 lights up red. When muting is turned on, each volume adjusting means is controlled to perform audio muting. Even when the selection of the input selector 74 is changed, this audio muting is automatically activated for 0.2 seconds, causing a fade-out to the input source before switching and a fade-in to the input source after switching. This prevents noise from being output. (8) Main volume 94 (gain adjustment operator) A variable resistor that divides a DC constant voltage is connected to the main volume 94, and the DC voltage value output from this variable resistor changes depending on the amount of rotation. This voltage value is A/D
After converting the amount of rotation to dB using a microcomputer (gain adjustment control means), set amounts of other volume adjustment operation means (gain adjustment operation element) (balance adjustment volume 96, muting key 92, input level The input level setting amount by the setting key 88) is calculated to determine the total gain, and from this total gain, each volume adjustment means (VCA 26, 32,
Digital volume 49, D/A conversion circuit 56,
The gain distribution of the digital volume (digital volume in 58) is determined, and the volume is adjusted by converting dB→Vc (VCA control voltage) and dB→step signal (digital volume control signal), and controlling the gain of each of them. A motor is connected to the main volume 94, and the volume can be adjusted by remote control. (9) Balance adjustment volume 96 This is a volume for adjusting the left and right balance of the main signal and sound field effect signal. The amount of adjustment is processed by a microcomputer after A/D conversion, and the left-right balance is adjusted by adjusting each volume adjusting means. (10) Digital equalizer parameter setting section 10
0 This is the part where parameters of the digital equalizer 42 (FIG. 2) are set. Here, the sixth
As shown in the figure, the band is divided into three bands: low, middle, and high, and the center frequencies _L , _M , _H ,
Level and Q can be set. It is also possible to set the cutoff frequency _C and slope for low cut and high cut. The center frequencies _L , _M , and _H of each band can be set in 1/6 oct steps within the following ranges. _L : 20~500Hz _M : 100~5kHz _H : 1k~20kHz However, it is set under the condition of _L < _M < _H. The level is -6 to + in 0.1dB steps for each band.
Set in a range of 6dB. Q is set to 0.7, 1.0, 1.4, 2.0, or 3.0 for each band. The low-cut and high-cut frequencies _C are set in the ranges of 20 to 200 Hz and 5 k to 18 k, respectively, and the slope thereof is set to 12, 18, or 24 dB/octave. FIG. 7 shows an enlarged view of the digital equalizer parameter setting section 100. This parameter setting section 100 has an operation section 101 at the bottom and a display section 102 at the top. The display section 102 displays the set values of each of the above parameters, and is composed of an LCD with a backlight. Of the parameters of the three divided bands, this display 102 displays each center frequency _L , _M , _H graphically on a scale, and displays the level and Q numerically. Since it is necessary to perform a huge amount of calculations in order to completely display the comprehensive frequency characteristics graphically, this is simply displayed, and the above configuration is adopted in consideration of the following points. Since the center frequency is divided into three bands, it is preferable to display it graphically on a scale in order to know the mutual positional relationship. Levels have long been familiar even when expressed numerically, and are easy to recognize and understand. Q is generally difficult to understand, but if it can be recognized, it is sufficient for the purpose of reproducing characteristics. With such a configuration of the display section 102, it is possible to easily display frequency control characteristics that are easy to use and understand. In the display section 102, the frequency scale 104 at the top displays the set values of frequencies _L , _M , and _H in each band.
Among the ▼ marks 104a arranged in a row above the
The positions of the set frequencies _L , _M , and _H are displayed in three locations. Among the numerical displays, the left part 105 shows the low-cut frequency in the upper row and its slope (12, 18, 18,
24dB/oct) are displayed respectively.
In the center section 106, the level is displayed in the upper row, and the Q is displayed in the lower row for the low range, middle range, and high range from the left. In the right part 108, there is a high-cut frequency in the upper row,
The slope (12, 18, or 24 dB/oct) is displayed in the lower row. The operation unit 101 includes the following various keys each consisting of a tact switch for setting parameters. Equalizer on/off key 110 This is a key for turning on/off the function of the digital equalizer 42. When this key 110 is turned off, the characteristics of the digital equalizer 42 become flat. Furthermore, when the analog source 10 is input, the analog straight path 12 is utilized as the main signal path (FIG. 2).
Note that even if the switch is turned off, the parameter value before the switch is turned off is retained in the memory. Also, when this key 110 is turned off, the sound field processor 20
When the sound field effect on/off key 135 (FIG. 4) is turned off, the display on the display unit 102 disappears and the backlight also disappears. The state at this time is shown in FIG. Further, when the sound field processor 20 is turned on, only the frequency scale 104 is displayed (none of the upper ▼ marks 104a are displayed, indicating that the characteristics are flat). When the equalizer on/off key 110 is turned on (it is also turned on by operating other equalizer-related keys 112, 114, etc.), each parameter returns to the state before it was turned off. Frequency key 112, Q/slope key 114 These keys are used to select the setting mode, and are pressed to set the center frequency, Q, or slope, respectively. If neither is pressed, the mode will be set to level setting mode. UP/DOWN key 116 This key is used to raise/lower each set value.Press the right side to raise it, and press the left side to lower it. Low-cut key 118 A key for setting low-cut characteristics. After pressing this key 118, pressing the frequency key 112 and operating the up/down key 116 sets the low-cut frequency. Also, low cut key 11
After pressing 8, the user presses the Q/slope key 114 and operates the up/down key 116 to set the low cut slope. The low cut key 118 is of a toggle type. That is, it turns on/off every time it is pressed. When it is off, the slope of the low cut becomes flat and the display on the display section 105 also disappears. Further, the operation of the up/down key 116 is no longer accepted. When turned on from off, the previous setting value is displayed. Low key 120, mid key 122, high key 124 These keys are used to set the characteristics of the three divided bands, and correspond to the low range, middle range, and high range, respectively. By pressing the low key 120 and operating the up/down key 116, the low frequency level is set. After pressing the low key 120, the frequency key 112
By pressing and operating the up/down key 116, the center frequency _L of the low range is set. Further, by pressing the low key 120, pressing the Q/slope key 114, and operating the up/down key 116, the low-frequency Q is set. For the midrange and high range, the midrange key is 122.1.
Each parameter can be set by pressing 24 and performing the same operation. High-cut key 126 A key for setting high-cut characteristics.The high-cut frequency and slope are set by the same operation as the low-cut key 118. Furthermore, when turned off, the slope of the high cut becomes flat, the up/down key 116 no longer accepts operation, and the display on the display section 108 disappears. (The setting value before turning off is retained in memory.) (11) Sound field effect operation section 130 This is the section for calling the sound field effect program, changing parameters, etc., and has two display sections 132 and 9.
0 and various operation keys. The display unit 132 displays the factory program and user program numbers (1 to 16) of 16 types stored in the sound field processor 20 (FIG. 2), and whether the program is a factory program or not. It is made up of LEDs to indicate whether it is a user program or not. The display section 90 displays the called program name, parameter setting values, etc., and is composed of LEDs. The various keys (all tact switches) of the sound field effect operation section 130 will be explained. Main mute key 132 This is a toggle type key that turns on/off the output of the main signal. The LED indicator 134 lights up during mute. Effect key 136 This key turns on/off the output of the sound field effect signal.
It is a toggle type. The LED indicator 138 lights up during mute. Sound field effect on/off key 135 This is a key for turning on/off the sound field sound effect creation process. When turned on, sound field sound effects are created; when turned off, sound field sound effects are no longer created (the state before turning off is maintained). If you turn it on from the off state (other sound field effect related keys 140, 144, 146
It can also be turned on by ), returns to the state before turning off. When turned off, the digital equalizer 42 is also turned off (operated with the equalizer on/off key 110).
If the digital equalizer 42 is on, the display section 90 will display nothing, and if the digital equalizer 42 is on, the display section 90 will display "DSP OFF"("DSP" means the sound field processor 20). be done. Parameter selection key 140 This key is used to select the type of parameter when changing the parameters of the sound field effect, and each time the key is pressed, the type of parameter is selected in order. For example, the following sound field effect parameters are provided. ○B Room size A parameter that corresponds to the dimensions of a room; the larger the value, the larger the space. Stretch or shorten the time axis of early reflections. ○B Liveness The value of the attenuation characteristic of early reflected sound. The higher the value, the longer the decay time becomes, making it live. ○High initial delay Changes the time difference between the start of direct sound and reflected sound. This is an important parameter that determines the positional relationship between the direct sound and the listening point in the sound field. If you reduce this value, the sound will be felt closer to the wall of the reproduced sound field (for example, inside a church), and if you increase it, the distance to the wall will be felt.
The optimal value differs depending on the source, early reflection data, and positional relationship between the main speaker and the sound field effect speaker, but by making subtle adjustments, the degree of connection from the on-stage sound image to the surrounding sound field can be controlled. ○D High-pass filter Cuts low frequencies at 6dB/octave. Set the frequency in 32 steps from through to 1kHz. ○Hollow pass filter Cuts high frequencies at 6dB/octave. Set the frequency in 36 steps from through to 1kHz. Effect level setting mode key 142 This is a key for setting the sound field sound effect level. Used to adjust the balance with the main signal. Effect front and rear balance setting mode key 14
4 This key is used to set the volume balance before and after the sound field sound effect. Select the mode using the up/down key 146, the parameter selection key 140, the effect level setting mode key 142, and the effect front/back balance key 144, and set the parameters, set the level of the sound field sound effect, and set the front/back balance of the sound field sound effect. This is what we do. If you press the left side, the set value will go down, and if you press the right side, the set value will go up. For example, if the parameter selection key 140 is operated, the parameter selection mode is entered;
Select the parameters in order by pressing /
By operating the down key 146, the value of each parameter is set. Also, if you operate the effect level setting mode key 142,
Consists of effect level setting mode, up/down
By operating the down key 146, the sound field sound effect level is set. Further, by pressing the effect front/back balance setting mode key 144, the effect front/back balance setting mode is entered, and by operating the up/down key 146, the front/back volume balance of the sound field sound effect is set. During these settings, the display unit 90 displays the setting mode name and setting value. Front/rear balance is displayed as a bar graph, and other settings are displayed as numerical values. Title edit key 148 This is a key for setting the name of the user program. When this key 148 is turned on, the display section 90
A cursor appears, and each time this key 148 is pressed, the cursor moves. And atup/
The down key 146 changes the character on the cursor and gives a name to the program created by the user. If a predetermined period of time elapses after this operation is stopped, or if another key is operated, the set program name is stored and this mode is canceled. Program key 150 A key for selecting one of 16 types of factory programs and 16 types of user programs. 16
Each key has one type of factory program and one type of user program assigned to it. The selected program number is displayed on the display section 13.
2. Preset key 152 A key for calling up a factory program. When pressed, the program key 150 becomes a factory program selection key. The name of the called program is displayed on the display section 9. User program key 154 A key for setting a program number when storing a user program or for calling a stored user program. When pressed, the program key 150 becomes a user program selection key. That is, when a user program is stored, the user program is stored in the number pressed by the program key 150, and when a user program is called, the user program stored in the number pressed by the program key 150 is stored. is called. The name of the stored or called program is displayed on the display section 90. Note that when the user program key 154 is pressed while the factory program is selected,
The previous last selected user program is read. Furthermore, when the preset key 152 is pressed while a user program is selected, the factory program that was last selected is read out. User program memory key 156 A key for storing a user program created by the user (created by calling a factory program and changing its parameters). When this is turned on, the "PROG.NO." display on the display section 132 flashes, and then by pressing any of the program keys 150, that program number will be displayed, including the user program sound field effect level, front/rear balance, and program. (The previous user program with that number will be deleted.) The factory program is a program related only to sound field effects, but
As the user program, a program related to sound field effects and the setting contents of the digital equalizer 42 at that time are stored as a set. That is, even if the factory program is called, the settings of the digital equalizer 42 do not change, but when the user program is called, the settings of the digital equalizer 42 when the user program is stored are also called at the same time. Next, in FIG. 2, "8A illustration", "8B illustration",
Detailed examples of each part indicated as "8C illustration" are shown in the corresponding drawings. [1] Figure 8A This is a part that includes an input terminal, an output terminal, and a selection circuit for input source and recording source output. There are 5 input terminals: 17 for digital signals (time-division input for left and right channels) and 1 for analog signals.
1a (for right channel), 11b (for right channel)
and 61 for video signals. In addition, the recording source output terminal is 50 for digital signals (time-division output for left and right channels).
, six each for analog signals 38a (for the left channel) and 38b (for the right channel), and two for video signals 62. Each input source is connected to these input terminals and audio recording source output terminal as shown in the table below.

〔Effect of the invention〕

As explained above, according to the present invention, gain adjustment is performed separately in the attenuators at the front and rear stages of the digital processing circuit, and when the total gain is made to be approximately 1 or more, the attenuators at the rear stage are adjusted to approximately 1.
When adjusting the gain at the front stage and making the overall gain approximately 1 or less, the attenuator at the front stage has a gain of approximately 1, and the attenuator at the rear stage adjusts the gain (attenuation amount).
By adjusting the , the following effects can be obtained. When the total gain is large, the attenuator at the subsequent stage has a gain of approximately 1, so the noise level generated in the digital processing circuit is not increased. The S/N ratio of the digital processing circuit itself is also good. When the total gain is small, the attenuator at the front stage has a gain of approximately 1, so the input to the digital processing circuit is not attenuated, and deterioration of the S/N ratio in that part is prevented to a minimum. Further, even if noise occurs in the digital processing circuit, it is attenuated by the attenuator at the subsequent stage, so the noise level itself becomes small.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention. FIG. 2 is a block diagram showing one embodiment of a control amplifier to which the present invention is applied.
This figure shows an outline of the specific circuit shown in FIG. A, FIG. 8B, and FIG. 8C. FIG. 3 is a diagram showing the principle of the sound field effect system incorporated in the control amplifier shown in the embodiment. FIG. 4 is a front view showing the configuration of the front panel of the control amplifier used in the embodiment. FIG. 5 is a front view showing an example of the display on the display section 90 on the front panel of FIG. 4, when the input level is set. FIG. 6 shows an example of filter characteristics of the digital equalizer 42 set by the digital equalizer parameter setting section 100 on the front panel of FIG. 4. FIG. 7 is an enlarged view of the digital equalizer parameter setting section 100 on the front panel of FIG. 4. FIG. 8A, FIG. 8B, and FIG. 8C are detailed views of each part indicated by the same figure number in FIG. FIG. 9 is a plan view showing an example of the arrangement of speakers, etc. in a listening room to which the control amplifier shown in this embodiment is applied. FIG. 10 is a block diagram showing gain distribution within the control amplifier shown in the embodiment. FIG. 11 is a diagram illustrating the gain distribution in FIG. 10. FIG. 12 is a diagram showing the noise level according to the gain distribution shown in FIG. 10.
FIG. 13 is a block diagram showing an example of the configuration of the dithered A/D conversion circuit 266 in FIG. 8C.
FIG. 14 shows the D/A conversion circuit 5 in FIG. 8C.
6 is a block diagram showing a configuration example of No. 6; FIG. FIG. 15 is an explanatory diagram of the operation of the D/A conversion circuit 46 in FIG. 8C. FIG. 16 is a diagram showing the display state in the digital equalizer parameter setting section 100 when the equalizer on/off key 110 is turned off in the control amplifier shown in the embodiment. FIGS. 17 and 18 are block diagrams showing the configurations of gain adjustment circuits each including the problems to be solved by the present invention. 1...Digital processing circuit, 3...A/D converter, 4...Digital processing section, 5...D/A converter, 6...Analog amplifier and analog attenuator (analog amplifier and first analog attenuator) 7... Analog attenuator (second analog attenuator), 8... Gain control circuit.

Claims (1)

[Claims] 1. An analog amplifier and a first analog attenuator into which an analog signal is input, and an analog amplifier and a first analog attenuator that convert the outputs of the analog amplifier and the first analog attenuator into digital signals after A/D conversion and digital signal processing. A digital signal processing circuit that converts and outputs the signal, and a second circuit that inputs the output of this digital signal processing circuit.
an analog attenuator, and a total gain in signal level transmission between the analog amplifier and the input of the first analog attenuator and the output of the second analog attenuator, a rated gain greater than 1 and a rated gain greater than 1. a gain adjustment operator that instructs an arbitrary value between an extremely small maximum attenuation gain; The gain of the second analog attenuator is set to approximately 1, and the overall gain in audio signal level transmission between the analog amplifier and the input of the first analog attenuator and the output of the second analog attenuator is set to approximately 1. Gain distribution is performed to set the attenuation amount of the first analog attenuator so as to match the overall gain instructed by the gain adjustment operator, and the overall gain instructed by the gain adjustment operator is equal to the gain 1 and the maximum gain. If the gain is between the attenuation gain, the gain of the first analog attenuator is set so that the total gain of the gain of the analog amplifier and the gain of the first analog attenuator is approximately 1. and the total gain in audio signal level transmission between the input of the analog amplifier and the first analog attenuator and the output of the second analog attenuator matches the total gain instructed by the gain adjustment operator. and gain adjustment control means for performing gain distribution to set the amount of attenuation of the second analog attenuator.