JP3296583B2 - Audio signal processing equipment - Google Patents

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 a sound image localization by performing processing such as compression and expansion on an input signal.

[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, signals having different phases can be combined, the pitch can be changed, and various signal processing can be performed.

[0004] By the way, various types of processing methods such as compression and decompression can be considered depending on which level range is changed and how. Examples of the type include a compressor, a noise gate, a limiter, and an expander.

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

[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 -} It becomes ¹ .

As described 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 = mcSin

FIG. 3 shows an example of a digital signal processing apparatus to which the digital signal processing circuit having the basic configuration of FIG. 1 is applied, and uses a compressor as a processing method. As shown in the figure, when the respective levels of the input signals from ch (channels) 1 to 4 are detected by the level detectors 1a to 4a, the coefficients corresponding to the detection results are transmitted from the coefficient controllers 1b to 4b. Coefficient multiplier 1
c to 4c.

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

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

[0013]

As described above, in the conventional digital signal processing apparatus described above, each of the ch1
The level of the input signal from each of the input signals from
a to 4a, and a coefficient corresponding to the detection result is output from the coefficient control units 1b to 4b to the coefficient multipliers 1c to 1c.
4c, the respective coefficient multipliers 1c
4c output signals with reduced dynamic range.

However, since the coefficients corresponding to the detection results output from the coefficient control units 1b to 4b are different from each other, the calculation results performed in the coefficient multipliers 1c to 4c are also different, and the respective R and L values are different. , C, S outputs differ in the amount of compression and decompression, resulting in a difference from the original sound image localization.

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

[0016]

In order to achieve the above object, an audio signal processing apparatus according to the present invention comprises: level detection means for separately performing level detection on input signals from a plurality of channels; 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 means for unifying the level control amount.

[0017]

In the audio signal processing apparatus of the present invention, the difference from the original sound image localization is improved by unifying the level control amounts for the respective channel outputs. A predetermined value is obtained, and level control amounts of input signals from a plurality of channels are unified by a coefficient signal based on the predetermined value.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings described below, portions common to FIG. 3 are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 4 shows an embodiment of the audio signal processing apparatus according to the present invention. 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, it outputs this value to the coefficient control unit 6.

The coefficient control unit 6 outputs the coefficient corresponding to the maximum value from the operation unit 5 to the coefficient multipliers 1c to 4c, so that the coefficient multipliers 1c to 4c can operate the channels 1 to 4 with the same level control amount. The compression processing is performed on the input signal from.

The signal whose dynamic range is reduced by the same level control amount by the coefficient multipliers 1c to 4c is
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 detectors 1a to 4a.

As a method of waveform detection in each of the level detectors 1a to 4a, generally, peak value detection, average value detection,
rms (effective value).

For example, when the average value detection is adopted, a low-pass filter (LP
F) smoothes the input signal. In this case, the attack time is set to be fast (short rise time constant) and the release time is set to be slow (long fall time constant).

By the way, the shorter the time constant is, the better the response is, and the accuracy of level detection is improved.
Since the detection level tends to fluctuate on the control unit side operating using this, the distortion rate as a whole deteriorates. In addition, when the attack time and the release time are set to the same time constant, smoothing accuracy decreases as the frequency becomes lower, so that a ripple occurs in the level detection, leading to a deterioration in the distortion factor.

From the above, each level detector 1a
The time constants of 4a to 4a are as small as possible within a range in which the distortion rate does not deteriorate.

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 by calculation,
This value is output to the coefficient control unit 6.

The coefficient control section 6 outputs the coefficient corresponding to the maximum value from the arithmetic section 5 to the coefficient multipliers 1c to 4c, so that the coefficient multipliers 1c to 4c have the same level control amount as the ch1 to ch4. Performs compression processing on the input signal from.

Here, the coefficient characteristics in the coefficient control section 6 are as shown in FIG. 6, for example. That is, the compression ratio k
Is in the range of 0 to 1. On the other hand, when the compression ratio k is equal to or smaller than the threshold level Lth, the compression ratio k is set to a constant value. When k> Lth, the compression ratio k is set to a value that follows a sharp decrease curve.

The multiplication coefficient according to FIG.
Are output to the coefficient multipliers 1C to 4C, for example, the characteristics of the characteristic shown in FIG. 7 are output from the coefficient multipliers 1C to 4C.

As a result, each of R, L, C, and S is converted into a signal having a reduced dynamic range by the same level control amount and is output, so that 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 arithmetic unit 5 obtains, for example, the maximum value from these detection results to perform coefficient control. The coefficient control unit 6 outputs a coefficient corresponding to the maximum value, so that the coefficient multipliers 1c to 4c perform compression processing on the input signals from ch1 to ch4 with the same level control amount. It was made to do.

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

In this embodiment, the case has been described in which the arithmetic unit 5 finds, for example, the maximum value based on the detection results of the level detectors 1a to 4a. Alternatively, other unified values may be obtained.

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

Further, in this embodiment, the case where the level detectors 1a to 4a are provided corresponding to the respective channels 1 to 4 has been described. However, the present invention is not limited to this example, and one level detector is provided. May be provided with a function of detecting the level from the channel of.

Further, in this embodiment, the case where the present invention is applied to a compressor which is one of the digital signal processing methods has been described. However, the present invention is not limited to this example, and other embodiments such as a noise gate, a limiter, an expander, and the like may be used. The method may be applied.

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

The BPFs 7a, 8a, 9a, 10a are respectively composed of BPFs 7a1-7a3, BPFs having different pass bands.
8a1 to 8a3, BPF9a1 to 9a3, BPF10a
1 to 10a3. Each of the level detectors 1a to 4a includes a level detector 1a1 to 1a3, a level detector 2a1 to 2a3, and a level detector 3a1 to 3a3.
, And level detectors 4a1 to 4a3.

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

BPFs 7a1, 8a1, 9a1, 10a1
... Pass band: ~ 200Hz BPF 7a2, 8a2, 9a2, 10a2 ... Pass band: 200Hz ~ 2KHz BPF 7a3, 8a3, 9a3, 10a3 ... Pass band: 2KHz ~ Level detectors 1a1, 2a1, 3a1, 4a1・ ・ Attack time: 40msec, release time: 2sec
c

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

Each of the BPFs having such characteristics
When the levels of the input signals of ch1 to ch4 that have passed through 7a to 10a are detected by the level detecting units 1a to 4a, the detection results are sent to the arithmetic unit 5. The arithmetic unit 5 obtains, for example, the maximum value from these detection results in the same manner as described 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 characteristics in the coefficient control section 6 are, for example, as shown in FIG. The multiplication coefficients according to FIG.
When output to 4C, coefficient multipliers 1C to 4C output, for example, the characteristics shown in FIG.

FIG. 8 shows that the level of the input signal is -3 dB,-
It shows the [distortion-frequency characteristics] at 20 dB, which is compared with the conventional characteristics.

As can be seen from the figure, the characteristics of the present embodiment shown by the solid line are substantially flatter in the entire input signal compared to the conventional one shown by the dotted line, and the deterioration of the distortion factor at 1 KHz or less is reduced. It turns out that it is considerably improved.

By the way, in the conventional average detection,
By simply setting the attack time to be fast (the rise time constant is short) and the release time to be late (the fall time constant is long), the responsiveness is improved and the level detection accuracy is improved. Since the detection level tends to fluctuate on the side of the control unit, the distortion rate deteriorates at about 1 KHz or less.

As described above, in this embodiment, the input signals are converted into BPFs 7a1 to 7a3, BPs having different pass bands, respectively.
F8a1-8a3, BPF9a1-9a3, BPF10
The frequency band is divided into a plurality of bands by a1 to 10a3, and the levels of the respective divided bands are level detectors 1a1 to 1a3, level detectors 2a1 to 2a3, and level detectors 3a1 to 3a.
3. Detection is performed by the level detectors 4a1 to 4a3.

As a result, the fluctuation of the detection level with respect to the low frequency is reduced, and the distortion in the low frequency band is reduced. Therefore, it is possible to improve the sound quality of the reproduced sound of the R, L, C, and S outputs. it can.

[0050]

As described above, according to the audio signal processing device of the present invention, a predetermined value is obtained from the detection result from each level detection means, and a coefficient signal based on the predetermined value is used to obtain a predetermined value 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 a difference from the original sound image localization can be prevented.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing input / output characteristics in the case of using a compressor in the audio signal processing of FIG. 1;

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

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

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

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

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

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

[Explanation of symbols]

 1a to 4a Level detector 1c to 4c Coefficient multiplier 5 Operation unit 6 Coefficient control unit

Claims (1)

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