JPH05244700A - Audio signal processor - Google Patents

Abstract

PURPOSE:To prevent a difference between a sound image localization position and an intrinsic one. CONSTITUTION:Level detectors 1a-4a detects the levels of input signals from (ch) 1-4, an arithmetic unit 5 searches the maximum value from the detected result, and outputs it to a coefficient control part 6, and the coefficient control part 6 outputs a coefficient corresponding to the maximum value, so that a compressing processing can be operated to the input signals from the (ch) 1-4 by the same level control amount by each coefficient multiplier 1c-4c. Then, the input signal from each (ch) 1-4 to which the compressing processing is operated by the coefficient multipliers 1c-4c, has the same level control amount, so that each R, L, C, and S output can be a signal in the same level. Thus, the difference between the sound image localization position and the original one can be reduced, and the sound image localization position can be faithful.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal processing apparatus for clarifying sound image localization, for example, by subjecting an input signal to processing such as compression and expansion.

[0002]

2. Description of the Related Art Various effects can be obtained in a digital circuit by an audio signal processing technique for performing processing such as compression and expansion on an input signal.

For example, by passing through a digital signal processing circuit, it is possible to combine signals having different phases, change the pitch, and perform various signal processing.

By the way, various types of processing methods such as compression / expansion can be considered depending on how to change the range of which level. Types include compressors, noise gates, limiters, expanders, and the like.

FIG. 1 shows a basic configuration of a digital signal processing circuit that uses a compressor as a method of processing such as compression and expansion. The level of an input signal is detected by a level detection section 1A, and a coefficient corresponding to the detection result is obtained. Is output from the coefficient control unit 1B to the coefficient multiplier 1C, the coefficient multiplier 1C subjects the input signal to compression processing based on the coefficient and outputs the compressed signal.

[0006] As shown in FIG. 2, if the input signal is a dynamic range when Sin is equal to or larger than the threshold Sth, compressed relative to that of the input to the k (0 ≦ k ≦ 1) , the Sout = Sin ^k ..

[0007] from the configuration of FIG. 1, the output signal Sout is the input signal Sin, since given by multiplying the coefficient mc, coefficients to be multiplied, mc = Sin ^{k -} is given by ^1.

[0008] By contrast, below the input signal Sin is the threshold, since input and output is a linear relationship, Sout = CSIN becomes a constant in the c, because c is equal to mc at the threshold, c = Sth ^{k -} Becomes ¹ .

From the above, the multiplication coefficient mc for the input signal
And the output signal Sout ^{is, mc = Sin k - 1 (} Sin ≧ Sth) and mc = Sth ^{k - 1} (S
in ≦ Sth) Sout = mc Sin

FIG. 3 shows an example of a digital signal processing device when the digital signal processing circuit having the basic configuration of FIG. 1 is applied, and a compressor is used as a processing method. As shown in the figure, when the levels of the input signals from the ch (channels) 1 to 4 are detected by the level detection units 1a to 4a, the coefficients corresponding to the detection results are output from the coefficient control units 1b to 4b. Coefficient multiplier 1
It is output to c-4c.

The signals whose dynamic range has been reduced by the coefficient multipliers 1c to 4c are respectively R,
L, C, S outputs are provided.

Here, R and L are signals supplied to the left and right speakers. C is a signal supplied to the speaker located in the middle. S is a signal supplied to the speaker provided on the back side.

[0013]

As described above, in the above-described conventional digital signal processing device, each ch1
Level detector 1 detects the levels of the input signals from
a to 4a, and the coefficient control unit 1b to 4b detects the coefficient according to the detection result from the coefficient multiplier 1c to
4c to output the respective coefficient multipliers 1c
.About.4c output a signal with a reduced dynamic range.

However, since the coefficients corresponding to the detection results output from the coefficient control units 1b to 4b are different, the calculation results performed in the coefficient multipliers 1c to 4c are also different, and the respective R and L are different. , C, and S outputs have different compression / expansion amounts, resulting in a difference from the original sound image localization.

The present invention has been made in consideration of such circumstances, and an audio signal processing apparatus capable of preventing a difference from the original sound image localization by unifying the level control amount for each channel output. The purpose is to provide.

[0016]

In order to achieve the above-mentioned object, an audio signal processing device of the present invention comprises level detection means for individually performing level detection on input signals from a plurality of channels, and level detection means. Coefficient signal output means for obtaining a predetermined value from the detection result from the means, and outputting a coefficient signal based on the obtained predetermined value, and input signals from the plurality of channels based on the coefficient signal from the coefficient signal output means And a level control unit for unifying the level control amounts of the above.

[0017]

The audio signal processing apparatus of the present invention is intended to improve the difference from the original sound image localization by unifying the level control amount for each channel output. From the detection result from each level detection means, A predetermined value is obtained, and the level control amounts of the input signals from a plurality of channels are unified by the coefficient signal based on this predetermined value.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings described below, the same parts as those in FIG. 3 will be assigned the same reference numerals and overlapping explanations will be omitted.

FIG. 4 shows an embodiment of the audio signal processing apparatus of the present invention, in which the levels of the input signals from the channels 1 to 4 are detected by the level detectors 1a to 4a. .. When the calculation unit 5 obtains, for example, the maximum value from the detection results of the level detection units 1a to 4a, this value is output to the coefficient control unit 6.

The coefficient control unit 6 outputs the coefficient corresponding to the maximum value from the calculation unit 5 to the coefficient multipliers 1c to 4c, so that the coefficient multipliers 1c to 4c have the same level control amount and ch1 to ch4. The input signal from is compressed.

The signals whose dynamic range has been reduced by the same level control amount by the coefficient multipliers 1c to 4c are:
The outputs are R, L, C and S, respectively.

In the audio signal processing device having such a configuration, when the input signals from the channels 1 to 4 are input, the respective levels are detected by the level detection units 1a to 4a.

Generally, peak value detection, average value detection, and waveform detection method in each of the level detection sections 1a to 4a are performed.
There is rms (effective value).

For example, when the average value detection is adopted, a low pass filter (LP) having a low cutoff frequency is used.
The input signal is smoothed by F), and the attack time in this case is set to be fast (the rising time constant is short) and the release time is set to be slow (the falling time constant is long).

By the way, the shorter the time constants, the better the responsiveness, and the level detection accuracy is improved.
On the side of the control section operating using this, the detection level is likely to fluctuate, and the overall distortion rate deteriorates. Further, when the attack time and the release time are set to the same time constant, the accuracy of smoothing becomes worse in the lower range, so that a ripple is generated in the level detection, which leads to deterioration of the distortion rate.

From the above, each level detector 1a
The time constants up to 4a are set to values as small as possible within the range where the strain rate does not deteriorate.

From each of the level detectors 1a to 4a to ch1 to ch4
When the detection result of the level of the input signal is output, the calculation unit 5 calculates, for example, the maximum value of each detection result,
This value is output to the coefficient control unit 6.

The coefficient control unit 6 outputs the coefficient corresponding to the maximum value from the calculation unit 5 to the coefficient multipliers 1c to 4c, so that the coefficient multipliers 1c to 4c have the same level control amount and ch1 to ch4. The input signal from is compressed.

Here, the coefficient characteristic in the coefficient control unit 6 is as shown in FIG. 6, for example. That is, the compression rate k
Is in the range of 0 to 1. With the threshold level Lth as a boundary, the compression rate k is set to a constant value when k ≦ Lth, and when k> Lth, a value that follows a rapid decrease curve is set.

The multiplication coefficient according to FIG. 6 is the coefficient control unit 6
From the coefficient multipliers 1C to 4C, the coefficient multipliers 1C to 4C output the characteristics shown in FIG. 7, for example.

As a result, the respective R, L, C, and S are output as signals whose dynamic range has been reduced by the same level control amount, and the sound image localization becomes clear.

As described above, in this embodiment, the level detectors 1a to 4a detect the levels of the input signals from the channels 1 to 4, and the calculator 5 obtains a maximum value from these detection results, for example, to perform coefficient control. The coefficient control unit 6 outputs the coefficient corresponding to the maximum value to the unit 6, and the coefficient multipliers 1c to 4c perform compression processing on the input signals from the channels 1 to 4 with the same level control amount. I was allowed to do it.

Therefore, since the input signals from the respective channels 1 to 4 compressed by the coefficient multipliers 1c to 4c have the same level control amount, the respective R, L, C and S outputs are signals of the same level. Therefore, the blur of the sound image localization is eliminated and the sound image localization is made clear.

In this embodiment, the case where the calculation unit 5 obtains, for example, the maximum value based on the detection results of the level detection units 1a to 4a has been described, but the present invention is not limited to this example. Other unified values may be obtained.

In this embodiment, the case where the input signal is four channels of ch1 to ch4 has been described, but the present invention is not limited to this example and may be three channels or less or five channels or more.

Further, in this embodiment, the case where the level detecting sections 1a to 4a are provided in correspondence with the respective ch1 to 4 has been described, but the present invention is not limited to this example, and one level detecting section is provided, and each of them is provided. You may make it have the function to detect the level from the ch of.

Furthermore, in this embodiment, the case where the present invention is applied to the compressor which is one of the methods of digital signal processing has been described, but the present invention is not limited to this example, and other noise gates, limiters, expanders and the like can be used. It may be applied to the method.

FIG. 5 shows another embodiment in which the configuration of the audio signal processing device of FIG. 4 is changed. BPFs 7a, 8a, 9 are provided on the input sides of the respective level detectors 1a-4a.
a and 10a are provided.

The BPFs 7a, 8a, 9a and 10a are BPFs 7a1 to 7a3 and BPFs having different pass bands.
8a1 to 8a3, BPF9a1 to 9a3, BPF10a
It is composed of 1 to 10a3. The level detectors 1a to 4a include level detectors 1a1 to 1a3, level detectors 2a1 to 2a3, and level detectors 3a1 to 3a3.
, Level detectors 4a1 to 4a3.

In the audio signal processing device having such a configuration, the characteristics of each BPF 7a, 8a, 9a, 10a and the level detecting portions 1a, 2a, 3a, 4a are set as follows, for example.

BPF 7a1, 8a1, 9a1, 10a1
... Pass band: ~ 200Hz BPF7a2, 8a2, 9a2, 10a2 ... Pass band: 200Hz to 2KHz BPF7a3, 8a3, 9a3, 10a3 ... Pass band: 2KHz to level detector 1a1, 2a1, 3a1, 4a1. ..Attack time: 40 msec, Release time: 2 se
c

Level detectors 1a2, 2a2, 3a2, 4
a2 ・ ・ ・ Attack time: 6 msec, Release time: 300 msec Level detector 1a3, 2a3, 3a3, 4a3 ・ ・ ・ Attack time: 2 msec, Release time: 100 m
sec

Each BPF having such characteristics
When the levels of the input signals of channels 1 to 4 that have passed 7a to 10a are detected by the level detection units 1a to 4a, respectively, the detection results are sent to the calculation unit 5. The calculation unit 5 obtains, for example, the maximum value from these detection results in the same manner as above, and outputs the obtained maximum value to the coefficient signal generation unit 6. The coefficient control unit 6 outputs a coefficient signal corresponding to the maximum value to each of the coefficient multipliers 1C to 4C.

Here, the coefficient characteristic in the coefficient control unit 6 is as shown in FIG. 6, for example, similarly to the above. The coefficient coefficient according to FIG.
When output to 4C, the coefficient multipliers 1C to 4C output the characteristics shown in FIG.

In FIG. 8, the level of the input signal is -3 dB,-
It shows the [distortion-frequency characteristic] when it is set to 20 dB, and is compared with the conventional characteristic.

As can be seen from the figure, the characteristic of this embodiment shown by the solid line is that the input signal is substantially flat over the entire area as compared with the conventional one shown by the dotted line, and the distortion factor deteriorates at 1 KHz or less. You can see that it has been improved considerably.

Incidentally, in the conventional average value detection,
By setting the attack time to be fast (the rising time constant is short) and the release time to be slow (the falling time constant is long), the response is improved and the level detection accuracy is improved. The detection level tends to fluctuate on the control unit side, and the distortion rate deteriorates at about 1 KHz or less.

As described above, in this embodiment, the input signals are supplied to the BPFs 7a1 to 7a3, BP having different pass bands.
F8a1 to 8a3, BPF9a1 to 9a3, BPF10
a1 to 10a3 divide the band into a plurality of bands, and the levels of the respective divided bands are detected by the level detectors 1a1 to 1a3, the level detectors 2a1 to 2a3, and the level detectors 3a1 to 3a.
3, the level detection units 4a1 to 4a3 are used for detection.

As a result, fluctuations in the detection level with respect to low frequencies are reduced, and distortion in the low frequency range is reduced, so that the sound quality of reproduced sounds of R, L, C, and S outputs can be improved. it can.

[0050]

As described above, according to the audio signal processing apparatus of the present invention, a predetermined value is obtained from the detection result from each level detection means, and a coefficient signal based on this predetermined value is used to output from a plurality of channels. By unifying the level control amounts of the input signals, the respective output levels are made the same, so that the difference from the original sound image localization can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of conventional audio signal processing.

FIG. 2 is a diagram showing an input / output characteristic when a compressor is used in the audio signal processing of FIG.

FIG. 3 is a block diagram showing an example of a digital signal processing device when the digital signal processing circuit having the basic configuration of FIG. 1 is applied.

FIG. 4 is a block diagram showing an embodiment of an audio signal processing device of the present invention.

5 is a block diagram showing another embodiment when the configuration of the audio signal processing device of FIG. 4 is changed.

6 is a diagram showing input / output characteristics when a compressor of the audio signal processing device of FIG. 4 is used.

7 is a diagram showing input / output characteristics when a compressor of the audio signal processing device of FIG. 4 is used.

8 is a diagram showing input / output characteristics of the audio signal processing device of FIG.

[Explanation of symbols]

 1a to 4a Level detection unit 1c to 4c Coefficient multiplier 5 Calculation unit 6 Coefficient control unit

Claims (1)

[Claims] 1. A level detection means for individually performing level detection on input signals from a plurality of channels, and a predetermined value obtained from a detection result from each level detection means,
Coefficient signal output means for outputting a coefficient signal based on the obtained predetermined value, and level control means for unifying the level control amounts of the input signals from the plurality of channels based on the coefficient signal from the coefficient signal output means. An audio signal processing device comprising: