JPH03218109A - Sound signal compressor - Google Patents

Abstract

PURPOSE:To revise the dynamic range of a sound signal with high accuracy by applying digital operation to a value corresponding to a level detected by a digital level detection means for the output of a digital delay means. CONSTITUTION:This compressor is provided with a digital delay means 10 delaying an input digital signal representing a sound signal digitally by a prescribed time, a digital level detection means 20 detecting the level of an input digital signal digitally and a digital arithmetic means 50 applying the digital operation to the value corresponding to the level value detected by the digital signal from the delay means 10 connected to the output of the digital delay means 10 and the digital level detection means 20. The operation is implemented by multiplying a larger value as the level of the input digital signal is decreased. Thus, the dynamic range of the input digital signal is compressed and the result is outputted and the revision of the dynamic range of a digital acoustic signal is realized with high accuracy.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an acoustic signal compressor device that changes the dynamic range of an acoustic signal such as an audio signal or a musical tone signal.

[Prior Art] Conventionally, this type of device utilizes analog signal processing, in which an input analog signal is input to a voltage-controlled amplifier, and an envelope of the input analog signal is input to a voltage-controlled amplifier.
is detected by a rectifying circuit and an integrating circuit, and the gain of the amplifier is controlled by the detection envelope, thereby changing the dynamic range of the input analog signal. [Problem to be Solved by the Invention 1] However, since the above-mentioned conventional device uses analog signal processing, the accuracy of each circuit element constituting the rectifier circuit and the integrating circuit, the voltage-controlled amplifier, etc. It was difficult to increase the dynamic range, and it was not possible to change the dynamic range with high precision. In addition, in conventional devices, there is a delay in envelope detection, so there is a time lag between the signal whose amplitude is actually controlled by the voltage-controlled amplifier and the envelope-detected signal. This difference also made it difficult to change the dynamic range with high precision. In such a case, it may be possible to place an analog delay element such as a BBD in the front stage of the voltage-controlled amplifier, but it is difficult to accurately grasp the delay time in envelope detection, and errors in the analog delay element also cause this problem. Even when changing the dynamic range with high precision was difficult. On the other hand, in recent years, many types of audio equipment have been performing digital signal processing, and in this case, since the audio signal is expressed digitally, the same signal It was desired to change the dynamic range while retaining the digital representation. The present invention was made based on the above problems and background, and an object thereof is to provide an audio signal compressor device that digitally changes the dynamic range of an audio signal and performs the same change with high precision. [Means for solving the problem] In order to achieve the above object, the first invention (claim 1 above)
The invention relates to digital delay means for digitally delaying an input digital signal representing an acoustic signal by a predetermined time, digital level detection means for digitally detecting the level value of the input digital signal, and an output of the digital delay means. The acoustic signal compressor device is constituted by a digital calculation means connected to the delay means for digitally calculating and outputting the digital signal from the delay means and a value corresponding to the level value detected by the digital level detection means. Further, the second invention (the invention according to claim 2) includes digital delay means for digitally delaying an input digital signal by a predetermined time for linearly displaying the acoustic signal, and digital delay means for digitally delaying the input digital signal by a predetermined time. A digital level detecting means for detecting and outputting the same level value in logarithmic representation, and a digital delay means that is connected to the output of the digital delay means and corresponds to the digital signal from the delay means and the logarithmically represented level value from the digital level detecting means. The acoustic signal compressor device is constructed by digital calculation means for digitally calculating and outputting the values. Furthermore, a third invention (the invention according to claim 3) is a sound signal compressor device according to the first or second invention, in which a digital level detection means and a digital calculation means are interposed between the digital level detection means and the digital calculation means. A level changing means is provided which controls and changes the level value from the level detecting means at a desired ratio and supplies it to the calculating means. Effects and effects of the invention] In the first invention configured as described above, when a digital signal representing an instantaneous value of an acoustic signal is input, the digital level detection means digitally converts the level value of the input digital signal. The digital calculation means digitally calculates the digital signal from the digital delay means and a value corresponding to the detection level value and outputs the result. In such a case, as the level value of the input digital signal becomes smaller, if an operation is performed in which the same signal is multiplied by a larger value, the dynamic range of the input digital signal will be compressed and output. Furthermore, in this case, the time required for level detection by the digital level detection means can be accurately grasped for digital signal processing, and the signal delay time by the digital delay means can also be accurately managed. If the digital delay means delays the input digital signal according to the time required for level detection by the digital level detection means, the value corresponding to the detected level can be accurately calculated for the level-detected digital signal. can be administered. All of these delays, detections, and calculations are digitally processed, and as mentioned above, it is possible to accurately calculate the value corresponding to the detection level on the level-detected digital signal. Errors caused by the precision of circuit elements, precision of delay time, etc., as in the prior art, are no longer included in the digital signal, and according to the first invention, it is possible to change the dynamic range of the digital acoustic signal with high precision. can. Further, the second invention operates in substantially the same manner as the first invention, but in this second invention, the input digital signal is displayed linearly, and the digital level detection means digitally displays the level value of the input digital signal. At the same time, the digital calculation means digitally calculates the digital signal from the digital delay means and the value corresponding to the logarithmically displayed level value, so that the digital acoustic signal is Variable control of the dynamic range is now performed using logarithmic expression (decibel expression). As a result, according to the second invention, in addition to the effects of the first invention, the dynamic range of the digital acoustic signal can be controlled over a wide range of signal levels, and the human auditory sense Corresponding controls will now be in place. Furthermore, in the third invention, the level changing means changes and controls the level value from the digital level detecting means at a desired ratio and supplies it to the digital calculation means, so that the compression ratio for the input digital signal can be controlled to change in various ways. Ru. As a result, according to the third invention, in addition to the effects of the first and second inventions, the degree of freedom in variable control of the dynamic range is increased, and it is possible to adapt to various audio devices and achieve various effects on audio signals. can be added, expanding the uses of the acoustic signal compressor device. Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of an acoustic signal compressor device according to the embodiment. This device includes a digital delay circuit 10. Digital level detection circuit 20, compression ratio setting circuit 30, multiplier 4
0 and a digital arithmetic circuit 50, it inputs a digital audio signal representing the instantaneous values of audio signals such as audio signals and musical tone signals in time series, and changes the dynamic range of the signal and outputs it. Incidentally, the digital acoustic signal is formed by linearly displaying each instantaneous value using "two's complement", and is composed of, for example, 16 bits. The digital delay circuit 10 is composed of a 16-bit shift register, and delays the input digital audio signal and outputs the delayed signal to the digital arithmetic circuit 50. In such a case, the number of stages of the shift register depends on the frequency of a clock signal (not shown) applied to the register for shift control, the digital level detection circuit 20 and the multiplier 40.
The digital processing circuit 50 is designed to calculate level control data formed on the input digital audio signal based on the detection level of the signal. The digital level detection circuit 20 has an absolute value circuit 21, as shown in detail in FIG. The absolute value circuit 21 has 15 exclusive OR circuits EX
Each exclusive OR circuit consists of EXOR circuits EXOR+~EX
O R +5 inputs the most significant bit MSB of the input digital audio signal to each one input, and inputs each bit of the same audio signal except the most significant bit MSE to each other input. 6 As a result, Positive input digital audio signal, e.g. rooo...01'' (16 bits)
excludes the most significant bit MSB “00...01J
(15 bits) signal. In addition, negative input digital acoustic signals, such as "111.
・IOJ (16 bits) excludes the most significant bit MSB, and inverts the bits other than MSB, ``OO...
- Output as OIJ (15 bits) signal. The input digital acoustic signal subjected to absolute value conversion (full wave rectification) in this absolute value circuit 21 is sent to an encoder 22 and a shifter 2.
3 and an inverter circuit group 24, the input digital acoustic signal is converted into data expressed in logarithms (decibels). The encoder 22 outputs the maximum value "11...IIJ" from the absolute value circuit 21.
(15 bits) is regarded as O decibels, and the exponent part of the logarithmic conversion data, which is a floating point representation of the same output, is displayed in 3 bits and output. That is, this encoder 22 converts the 15-bit data into 3-bit data representing rX-IJ, assuming that the X-th bit position is the bit position where "1" appears for the first time when looking at the 15-bit data from the highest order. It is composed of logic circuits. Note that this 3-bit data is “OOOJ. rooIJ ro10
J...rl 1 1j, O, -6, -
12...-42 decibels. As a result, the 15-bit data is converted as follows. r111111111...1''~r10000000
0...O” → roto” r011111111・
...1"~r010000000...0" → "0
01"r001111111・1"~r0010000
00...0” → “010” r000111111
・・1”～r00010000. o...0" → "
011"r000000011...1"~r0000
00010...0'' → The rllllJ shifter 23 outputs the mantissa part of the logarithm conversion data expressed as a floating point in 3 bits.
By bit-shifting the bit data to the upper side by the 3-bit data value from the encoder 22, the most significant bit MSB of the output is always "1", and the upper 2nd to 4th bits of the parentheses are Outputs 3-bit data. For example, the r111111111...
1"~r 100000000...0" is not bit-shifted, and the upper 2nd to 4th bits rllll"~"00
0'' 3-bit data is output, and the r0001
11111...1''~r000100000...0
” is shifted by 3 bints and the rl of the 2nd to 4th high-order bits is
3-bit data from llJ to "000" is output. Of course, in such a case, the 15-bit data from the absolute value circuit 21 is set to "1" from the output value from the encoder 22.
Alternatively, the upper three bits may be output by shifting the upper bits by a larger number of bits. The 3-bit mantissa data from the shifter 23 is combined with the 3-bit output data from the encoder 22 via an inverter circuit #24, and is output as 6-bit level data. The inverter circuit group 24 is the inverter circuit 11
r I NV+. INV2. It is composed of I Nv3 and inverts each bit output from the shifter 23 and outputs it. The reason for inverting the mantissa data in the inverter circuit group 24 is as follows. That is, as mentioned above, when creating the exponent part data, r l 1 +- 1..1'' ~ r 1000.
...0" data value is O decibel, r0111...1
"~ro100...0" data value -6 dB,
Convert the data values of "r0011...1" to "rooio...O" to -12 decibels, etc., and transfer the data values to the shifter 23.
As the mantissa data, the most significant bin} MSB “1
The data value of ``rllll''~rooOJ is always output. In such a case, the display of the mantissa data is equivalent to viewing the triangular hunting part of -6 decibels or less in FIG. 3 onto the triangular hatching part of O to -6 decibels. On the other hand, the O~
As shown in FIG. 4, which is an enlarged view of the -6 dB part, the smallest absolute value of the mantissa output from the shifter 23 is O dB (the maximum level) is r
l 1 1J, and -6 decibels as the largest absolute value (minimum level) is roO
OJ, the output of shifter 23 shows the opposite direction of change as a negative decibel display. Therefore, the inverter circuit group 24 converts the value of 0 to -6 decibels into roo
] to "111", a linear approximation is performed so that the value changes from "111" to "111" to match the exponent part data. As can be understood from this explanation, the 6-bit level data consisting of the exponent and mantissa parts is expressed as a negative decibel value whose absolute value increases as the absolute level of the input digital audio signal decreases. has been done. To this 6-bit level data, 4-bit digital data consisting of roooOJ is added on the lower side, that is, the 6-bit level data is extended to 10 bits and supplied to one input of the subtracter 25a. The subtracter 25a constitutes a part of the digital filter 25, and subtracts the level data from the delay circuit 25b (control clock is omitted) consisting of an l-stage 10-bit shift register and supplies the result to the multiplier 25c. In addition to these circuits 25a to 25c, the digital filter 25 includes an adder 25d, and the adder 25d includes a multiplier 25.
The output of c and the output of the delay circuit 25b are added and supplied to the input of the delay circuit 25b. This digital filter 25 uses the output of the subtracter 25a as a high-pass output and the output of the adder 25d as a low-pass output, and uses the gain coefficient g supplied to the multiplier 25c.
The cutoff frequency characteristic of the low bass output with respect to the input signal is controlled to change. That is,
As the gain coefficient g becomes larger, the cutoff frequency in the low-pass characteristic of the digital filter 25 becomes larger. The output of the subtracter 2'5a is connected to a positive/negative discrimination circuit 26a. The positive/negative determining circuit 26a is constituted by a comparator, and determines whether the result of subtraction by the subtracter 25a is positive or negative and outputs the result. The gain memory 26b is controlled by the positive/negative discrimination circuit 26a to supply a gain coefficient g to the multiplier 25c, and when the determination result is negative, it supplies a predetermined large gain coefficient g1 to the multiplier 25c, and the determination result is negative. When the result is positive, a predetermined small gain coefficient g2 (g+>g2)
is supplied to the multiplier 25c. As a result, when the absolute level of the input digital acoustic signal increases, the cant-off frequency in the low-pass characteristic of the digital filter 25 becomes higher as shown by the solid line in FIG. 5, and the envelope detection follows faster. Further, when the absolute level of the acoustic signal decreases, the cutoff frequency becomes lower as shown by the two-dot chain line in FIG. 5, and the tracking of the envelope detection becomes slower. This is because, although the level data expressed logarithmically by the encoder 22, shifter 23, and inverter circuit group 24 represents a negative decibel value, the sign bit representing the negative value of the data is omitted. The 10-bit digital data representing the envelope thus detected is output as level data from the digital level detection circuit 20 and supplied to the multiplier 40, as shown in FIG. In such cases,
The level data that was treated as representing a negative decibel value within the digital level detection circuit 20 (however, the sign pit representing negative is omitted) is treated as a positive value from the time it is output from the same detection circuit 20. be exposed. This is because the absolute level of the input digital audio signal is small, so the level data of the negative decibel display, which has a large absolute value, is treated as a positive value, thereby increasing the level of the audio signal with a small input level, and This is to easily realize the audio signal compressor device that reduces the level of an audio signal with a high input level and changes the dynamic range of the audio signal. The multiplier 40 multiplies the supplied level data by the compression rate control data supplied from the compression rate setting circuit 30 and outputs the result to the digital arithmetic circuit 50. The compression rate setting circuit 30 includes an operator for setting the compression rate and a data output circuit for outputting compression rate control data according to the operating position of the operator. A digital arithmetic circuit 50 converts the level of the 16-bit digital audio signal from the digital delay circuit 10 into a multiplier 4.
The output is raised by 10 bits of level data (in decibels) from 0, as shown in Figure 6.
It consists of a multiplier 51, an adder 52, and a shifter 53. The multiplier 51 and the adder S2 are in charge of calculations regarding the mantissa part of the level data. The multiplier multiplies the 7-bit mantissa part of the 10-bit level data supplied through the multiplier and outputs the result. The adder 52 has the 16
The bit digital audio signal and the multiplication result of the multiplier 40 are added and output. As a result, the level of the digital sound signal varies from 0 to 6, 6 to 12, as shown in FIG.
. . . Only the mantissa portion representing each increment between decibels is raised by a factor of 1 to 2 in linear representation by linear approximation. The chic 53 is in charge of calculations regarding the exponent part of the level data, and adds the addition result of the adder 52 by the number of upper bits corresponding to the value expressed by the 3-bit exponent part of the 10-bit level data. Shift to the side and output. For example, if the exponent part represents ro00J (0 decibels), the digital audio signal from the adder 17 is output as is. Also, the index part is ro11J
(18 decibels), the digital audio signal from the adder 17 is shifted to the upper side by 3 bits,
That is, the signal is multiplied by 8 in linear display and output. That is, by this shift operation, the level of the digital audio signal from the adder 17 is changed to O by the 3-bit exponent part.
The value is increased by 6 decibels from decibels to 42 decibels, that is, 1, 2, 4...128 times in linear display. According to the embodiment configured as described above, when a digital audio signal is input, the audio signal is supplied to the digital delay circuit 10 and the digital level detection circuit 20. This digital audio signal is delayed by a predetermined time by a digital delay circuit 10 and subjected to envelope detection by a digital level detection circuit 20. Then, the digital arithmetic circuit 50 changes and controls the dynamic range of the input digital audio signal by changing the level of the delayed input digital audio signal according to the level data representing the envelope. in this case,
All of these signal processes are performed digitally, and the delay time of the digital delay circuit 10 is set to the time required for the calculations of the digital level detection circuit 20 and the multiplier 40. Level change processing will now be performed accurately. As a result, errors caused by circuit element precision, delay time precision, etc. are not included in the digital signal, and the dynamic range of the digital acoustic signal can be changed with high precision. In addition, in detecting the envelope, in the digital level detection circuit 20, the absolute value circuit 21 performs processing equivalent to full-wave rectification in analog signal processing on the input digital acoustic signal, and then the encoder 22, shifter 23 and The inverter circuit group 24 converts the processed input digital audio signal into logarithmic display data using a floating point whose maximum level is O decibels, and the digital filter 2
5 is controlled by the positive/negative discrimination circuit 26a and the gain memory 26b to detect the envelope of the input digital sound signal by changing and controlling the cutoff frequency in the low bass characteristic according to the direction of change of the input acoustic signal. As a result, the envelope detection described above can be realized with a simple circuit configuration, and since the envelope detection value is displayed in decibels, the number of bits is small even if the dynamic range of the input digital audio signal is large, and it corresponds to the human auditory sense. It is expressed in the form of Further, the level data representing the envelope from the digital level detection circuit 20 is variably controlled in a multiplier 40 based on compression rate control data from the compression rate setting circuit 30, and then digitally delayed in a digital calculation circuit 50. It is used to control the level of the digital audio signal from the circuit 10, and the arithmetic circuit 50 obtains a digital audio signal whose dynamic range has been compressed in accordance with the compression ratio control data. That is, an input digital audio signal having a dynamic range as shown by the solid line in FIG. 8 is changed to a dynamic range as shown in the broken line, one-dot chain line, two-dot chain line, etc. in the same figure, and is output. This makes it possible to adapt to various types of audio equipment and to add various effects to audio signals, thereby expanding the uses of the audio signal compressor device. In the above embodiment, when the digital level detection circuit 20 converts linearly displayed data into logarithmic (decibel) display, the mantissa part is linearly approximated using the inverter circuit group 24 (FIG. 2). However, as shown in FIG. 9, by using a linear/logarithmic conversion table 24a in place of the same circuit group 24, the data in linear representation can also be converted into logarithmic (decibel) representation with respect to the data regarding the mantissa part. You can do it like this. In addition, in the above embodiment, when the digital arithmetic circuit 50 converts logarithmic (decibel) data to linear display, the mantissa part is linearly approximated using the multiplier 51 (FIG. 6). However, as shown in FIG. 10, by providing a logarithmic/linear conversion table 54 before the multiplier 51, logarithmic (decibel) data is converted to linear representation for the mantissa part as well. Good too. These eliminate errors caused by linear approximation in the above embodiments,
The accuracy of the acoustic signal compressor device is better. Further, in the above embodiment, the positive/negative discrimination circuit 26a (FIG. 2) detects the rise and fall of the input digital acoustic signal, but as shown in FIG. 11, in place of the discrimination circuit 26a, Input data to the digital filter 25 and a delay circuit 2 that delays the same data by 1 bit
The rise and fall may be detected by comparing the magnitude with the output of the output signal 6c using a comparator 26d. Next, an application example of the acoustic signal compressor device according to the above embodiment and its modification will be explained. FIG. 12 shows an acoustic signal compressor device 1 according to the present invention.
00 is incorporated into a digital audio system.The device 100 inputs a digital audio signal from a digital audio signal source 101 such as a disk or tape, changes its dynamic range, and outputs it. This acoustic signal compressor device 10
A D/A converter 102 is connected to the amplifier 10, and the converter 102 converts the digital audio signal whose dynamic range has been changed into an analog audio signal.
3 to the speaker 104 and output to the tape recorder 105. According to this, audio signals [1
The acoustic signal from 01 can be output from the speaker 104 by changing its dynamic range, and can be newly recorded on the tape recorder 105. Further, FIG. 13 shows the acoustic signal compressor device 100.
The device 100 changes the dynamic range of a digital musical tone signal generated from a musical tone signal forming circuit 112 in accordance with the operation of a performance operator 111 such as a keyboard, and outputs the same. . This digital musical tone signal whose dynamic range has been changed is converted into an analog musical tone signal by the D/A converter 113, and then sent to the amplifier 11.
4 to the subaker 115, and the subaker 11
From 5 onwards, it is pronounced as a musical note. As a result, a unique acoustic effect is added to the musical tone signal formed by the musical tone signal forming circuit 112. Further, FIG. 14 shows the acoustic signal compressor device 10.
0 is applied to an electric musical instrument, and the device 100
is connected via an A/D converter 123 to a pickup device 122 that pickups string vibrations of a musical instrument body 121 such as a guitar. The A/D converter 123 converts the big-up signal into a digital acoustic signal and outputs the signal to the acoustic signal compressor device 100.
supply to The acoustic signal compressor device 100 changes the dynamic range of the digital acoustic signal to
The signal is output to the A converter 124, and the D/A converter 124 converts the digital audio signal whose dynamic range has been changed into an analog audio signal, and supplies the analog audio signal to the speaker 126 via the amplifier 125. As a result, the speaker 126 produces an instrument sound with a changed dynamic range of the big-up signal, and a unique acoustic effect is added to the big-up signal.

[Brief explanation of drawings]

FIG. 1 is an overall block diagram of an acoustic signal compressor device according to an embodiment of the present invention, FIG. 2 is a detailed block diagram of the digital level detection circuit of FIG. 1, and FIGS. A graph for explaining the linear/logarithmic conversion operation in the circuit, FIG. 5 is a graph showing the low-pass characteristics of the digital filter in FIG. 2, FIG. 6 is a detailed block diagram of the digital arithmetic circuit in FIG. 1, and FIG. 7 is a graph for explaining the logarithmic/linear conversion operation in the circuit of Fig. 6, Fig. 8 is a graph showing the compression characteristics of the acoustic signal in the acoustic signal compressor device, and Fig. 9 is a graph for explaining the linear/logarithmic conversion operation of the circuit of Fig. 2. 10 is a detailed block diagram showing a modification of the logarithmic/linear conversion section in FIG. 6, and FIG. 11 is a modification of the digital acoustic signal change direction detection section in FIG. 2. Detailed block diagram showing examples, Figures 12-1
FIG. 4 is an overall block diagram showing an example of application of the acoustic signal compressor device. Explanation of symbols 10... Digital delay circuit, 20... Digital level detection circuit, 21... Absolute value circuit, 22... Encoder, 23... Shifter, 24... Inverter circuit group, 24a... Linear/logarithmic conversion table, 25.
...Digital filter, 26a...Positive/negative discrimination circuit,
26b... Gain memory, 26c... Delay circuit, 26
d... Comparator, 30... Compression rate setting circuit, 4o...
- Multiplier, 50...Digital arithmetic circuit, 51...
Multiplier, 52... Adder, 53... Shifter, 54.
...Log/linear conversion table.

Claims (3)

[Claims] (1) Digital delay means for digitally delaying an input digital signal representing an acoustic signal by a predetermined time, digital level detection means for digitally detecting the level value of the input digital signal, and an output of the digital delay means. An acoustic signal compressor device comprising: a digital calculation means connected to the delay means for digitally calculating and outputting a digital signal from the delay means and a value corresponding to the level value detected by the digital level detection means. (2) Digital delay means for digitally delaying an input digital signal by a predetermined time for linearly displaying an acoustic signal, and digitally detecting the level value of the input digital signal and outputting the same level value in logarithmic display. a digital level detection means; and a digital operation connected to the output of the digital delay means for digitally calculating and outputting a digital signal from the delay means and a value corresponding to a logarithmically expressed level value from the digital level detection means. 1. An acoustic signal compressor device comprising: means. (3) In the acoustic signal compressor device according to claim 1 or claim 2, an audio signal compressor is provided between the digital level detection means and the digital calculation means to convert the level values from the same level detection means into a desired ratio. An acoustic signal compressor device characterized in that it is provided with a level changing means for controlling the change and supplying the signal to the calculating means.