JPH05275950A - Dynamic range compressor for acoustic signal - Google Patents

Abstract

(57) [Abstract] [Purpose] When compressing the dynamic range of an acoustic signal due to CD (Compact Disc) reproduction or the like, it is possible to improve the excessive compression characteristics without deteriorating the distortion rate. The amplitude level of an acoustic signal is detected by using the compression coefficient switching means 16, and when the signal amplitude rapidly increases, the compression coefficient corresponding to the amplitude level is immediately used by the compression coefficient calculation means 15. The transient characteristics are improved by calculating and not playing a large volume instantaneously. The compression coefficient calculation means 1 is used only when the signal amplitude is sufficiently small.
By processing the compression coefficient calculated in step 5 so that it is used in the multiplication means 17, the distortion factor of the output signal is prevented from deteriorating even when the time variation of the compression coefficient is large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a compact disc,
The present invention relates to an acoustic signal dynamic range compression device in an acoustic information reproducing device that reproduces an acoustic signal from an information recording medium on which acoustic information having a wide dynamic range such as a laser disc, a digital audio tape, and a mini disc is recorded.

[0002]

2. Description of the Related Art FIG. 8 is a block diagram showing the function of a conventional acoustic signal dynamic range compression apparatus. In FIG. 8, an acoustic information recording medium 60 on which acoustic information having a wide dynamic range is recorded is reproduced by an acoustic signal reproducing means 61, an absolute value converting means 62, a smoothing means 63, and a dynamic range compression coefficient calculating means 64. Is input to the connected subordinates. The multiplication means 65 is input from the acoustic signal reproduction means 61 and the dynamic range compression coefficient calculation means 64, and outputs it to the acoustic speaker 66.

Next, the operation will be described. An input acoustic signal having a polarity generated by reproducing the acoustic information recording medium 60 by the acoustic signal reproducing means 61 is input to the absolute value converting means 62 and is made non-polarized. It is passed through a smoothing means 63 to detect the amplitude of the depolarized acoustic signal. Smoothing means 6
As 3, a low-pass filter having a cutoff frequency corresponding to the lower limit frequency (about 20 Hz) of audible sound is generally used. Since the signal after passing through the smoothing means 63 means the amplitude level of the input signal averaged by the time constant of the smoothing low-pass filter, the dynamic range compression coefficient corresponding to this amplitude level is calculated as the dynamic range compression coefficient. The smoothing means 63 is calculated by using the means 64, the coefficient is multiplied by the acoustic signal input from the acoustic signal reproducing means 61 by using the multiplying means 65, the result is output, and the result is converted into sound by the sound speaker 66. It is possible to generate an output signal in which the dynamic range of the input acoustic signal is compressed with an attack time (a kind of dynamic characteristic) determined by the time constant of the smoothing filter used in.

The attack time is a level at which a small input acoustic signal is input for a while and the compression coefficient is sufficiently stabilized, and then the input acoustic signal is switched to a large input acoustic signal, and then the compression coefficient is large. The time until it stabilizes is referred to here.

[0005]

(Problem 1) However, in the above-mentioned conventional acoustic signal dynamic range compression apparatus, if the time constant of the smoothing low-pass filter is reduced in order to improve the dynamic characteristic (attack time) of the apparatus. Ripple after smoothing becomes relatively large, especially several tens.
At frequencies below Hz, the variation of the coefficient becomes large, and especially when the coefficient is switched at a position where the input signal amplitude is large,
There is a problem in that the harmonic distortion component included in the output acoustic signal is increased and the output signal quality is degraded.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an excellent acoustic signal dynamic range compression apparatus having good dynamic characteristics without distortion.

(Problem 2) However, in the above-mentioned conventional acoustic signal dynamic range compression apparatus, since the dynamic range compression coefficient is updated by the time constant of the smoothing low-pass filter, after a small acoustic signal is reproduced for a while,
When a large acoustic signal is suddenly input, the gain must be negative, and the amplitude must be used.
Since the dynamic range compression coefficient maintains the coefficient in the area where the gain becomes positive for a while, as a result, a larger acoustic signal is output, and the operation opposite to the original purpose of extending the dynamic range is performed, In some cases, it causes saturation of the output acoustic signal and causes harmonic distortion,
There is a problem that the output signal quality is significantly reduced.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an acoustic signal dynamic range compression apparatus which normally compresses the dynamic range without distortion.

[0009]

Means for Solving the Problem (Means 1) In order to achieve the above-mentioned object (Problem 1), the present invention provides an amplitude or polarity change of an input acoustic signal between a dynamic range compression coefficient calculating means and a multiplying means. Is arranged to update the dynamic range compression coefficient at the time when the instantaneous value of the amplitude of the acoustic signal is small.

(Means 2) In order to achieve the above object (Problem 2), the present invention comprises an amplitude increase / decrease judging means for judging whether the acoustic signal amplitude has increased or decreased after the absolute value conversion means,
Switching means for switching between two smoothing means having different time constants is provided, a smoothing filter having a short time constant is used in the direction in which the amplitude of the input acoustic signal increases, and a long time as in the conventional case is used in the direction in which the signal amplitude decreases. It is configured to switch to a filter having a constant.

[0011]

(Operation 1) With the structure of (Means 1), the compression coefficient switching means monitors the instantaneous value of the input acoustic signal,
By updating the compression coefficient that changes from moment to moment when the amplitude of the input acoustic signal is small, that is, when the absolute amount of the distortion component becomes small, and when the amplitude of the input acoustic signal is large, the previously updated compression coefficient is maintained. Originally, the fluctuation of the compression coefficient becomes large, and the compression coefficient is switched at the moment when the instantaneous amplitude level of the input signal is large, and the distortion rate of the output acoustic signal may be deteriorated. Does not lower.

(Operation 2) With the configuration of (Means 2), the amplitude increase / decrease judging unit detects the increase / decrease of the signal amplitude, and when the amplitude of the input acoustic signal increases, the smoothing filter having a small time constant is input again. By controlling the switching means to switch to a smoothing filter with a large time constant when the amplitude of the acoustic signal decreases, the smoothing result is rapidly corrected in the direction in which the amplitude of the input acoustic signal increases. As the above-mentioned signal dynamic range compression coefficient is rapidly reduced, the operation of compressing the signal dynamic range becomes possible even for a large acoustic signal that suddenly occurs, and distortion is suppressed.

[0013]

(Embodiment 1) FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention. In FIG. 1, an acoustic information recording medium 11 in which acoustic information having a wide dynamic range is recorded is reproduced by an acoustic signal reproducing means 12, an absolute value converting means 13, a signal amplitude detecting means 14, and a dynamic range compressing coefficient calculating means. 15 and the compression coefficient switching means 16 are input to the subordinate connection.
The compression coefficient switching means 16 is also input from the audio signal reproducing means 12. The multiplying means 17 is inputted from both the acoustic signal reproducing means 12 and the compression coefficient switching means 16, and outputs it to the one in which the digital / analog converting means 18 and the acoustic speaker 19 are subordinately connected. Further, the audio signal reproducing means 12, the absolute value converting means 13, the signal amplitude detecting means 14, the dynamic range compression coefficient calculating means 15, the compression coefficient switching means 16 and the multiplying means 17 are blocks for digital processing and are synchronous timing signals. It is connected to 110.

Next, the operation will be described. Since the digital acoustic signal reproduced from the acoustic information recording medium 11 using the acoustic signal reproducing means 12 is a signal having polarity,
The absolute value conversion means 13 is used to make the signal non-polar, and the absolute value is converted to a signal indicating the magnitude of the signal in real time.
An average amplitude of the input acoustic signal is calculated using the signal amplitude detecting means 14 for the signal whose absolute value has been converted. Since the processing result of the signal amplitude detection means 14 is an amplitude value signal indicating the average amplitude of the input acoustic signal, the dynamic range compression coefficient corresponding to this amplitude is calculated using the dynamic range compression coefficient calculation means 15. .. Next, the compression coefficient switching means 16 is used to judge whether the multiplication means 17 actually uses the compression coefficient calculated above and update the compression coefficient. As this operation, the compression coefficient is adopted and updated when the instantaneous amplitude level of the input acoustic signal is small. On the contrary, when it is determined that the instantaneous amplitude level of the input acoustic signal is large, the compression coefficient used in the previous own determination is held. To determine whether the instantaneous amplitude level of the acoustic signal is small, a method of determining whether the amplitude of the input signal is less than or equal to a certain threshold value, and a value before one synchronization timing of the input acoustic signal are stored. It is conceivable that the compression coefficient is switched when the polarity of the input acoustic signal input at this time and the current synchronization timing is inverted. The digital / analog conversion means 1 multiplies the compression coefficient switched by the processing of the compression coefficient switching means 16 by the digital acoustic signal having the above-mentioned polarity.
It is sent to 8 and converted into an analog signal and converted into sound by the audio speaker 19. With the above operation, even when an acoustic signal of a low frequency having a possibility that the time variation of the dynamic range compression coefficient calculated by the dynamic range compression coefficient calculating unit 15 is large is input, the acoustic signal dynamic range compression is performed. It has the effect that the dynamic characteristics are improved while the distortion rate of the device deteriorates, and the emotional agitation of the listener can be alleviated.

FIG. 2 is a flow chart showing the processing flow of the first embodiment. In FIG. 2, 31 is a process for waiting for the synchronization timing, and 32 is the acoustic signal reproducing means 1 of FIG.
This is a process of inputting the acoustic signal (A _n ) detected in 2. Note that n is a subscript indicating n time. 33 is a process for converting an absolute value, 51 is a process for obtaining a time average of the absolute values B _n obtained in the process 33, and the smoothing means 6 in FIG.
It is realized by the processing of 3. 37 is a process for calculating the dynamic range compression coefficient CR _{n based} on C _n ; 52 is a process for determining whether or not the instantaneous amplitude level of the input acoustic signal is small; 53 is the compression coefficient CR _n used for compression This is a process of updating the coefficient CRR _n . 38 is a process for performing a product operation of the adopted compression coefficient CRR _n and the input acoustic signal, 3
9 outputs the result D _n of the product operation of the process 38 and returns to the process 31 waiting for the synchronization timing. The above processing is repeated at every synchronization timing. Flow charts of the respective processes 52 and 53 are shown in FIGS. 3 and 4 as specific processes. In FIG. 3, the magnitude of the instantaneous amplitude level of the input acoustic signal is judged by comparing B _{n with a} certain threshold,
The process of is a process of judging from the polarity change of the input acoustic signal A n at the time of _n and the input acoustic signal A _n-1 input at the synchronization timing of the previous time.

(Embodiment 2) FIG. 5 is a block diagram showing the configuration of the second embodiment of the present invention. In the figure, an audio information recording medium 11, an audio signal reproducing means 12, an absolute value converting means 13, a dynamic range compression coefficient calculating means 15, a multiplying means 17, a digital / analog converting means 18, an audio speaker 19 and a synchronization timing signal 110. 1 have the same reference numerals, names and functions as in FIG. 1 of the first embodiment.

The absolute value converting means 13 is the acoustic signal reproducing means 1
It is input from 2, and is output to the amplitude increase / decrease judging means 21 and the switching means 22. The switching means 22 switches the input to the digital filter arithmetic means 23 having a short time constant and the digital filter arithmetic means 24 having a long time constant in response to a command from the amplitude increase / decrease judging means 21 and outputs it. Digital filter calculation means 2
The outputs of 3 and 24 are input to the dynamic range compression coefficient calculation means 15 and the amplitude increase / decrease determination means 21. The multiplying means 17 is inputted from the acoustic signal reproducing means 12 and the dynamic range compression coefficient calculating means 15, and outputs it to the one to which the digital / analog converting means 18 and the acoustic speaker 19 are subordinately connected. Also, the audio signal reproducing means 12, the absolute value converting means 13, the amplitude increase / decrease judging means 21, the switching means 22, the short time constant digital filter calculating means 23, the long time constant digital filter calculating means 24, and the dynamic range compression coefficient calculating means. Reference numeral 15 and the multiplication means 17 are blocks that perform digital processing and are connected to the synchronization timing signal 110.

Next, the operation will be described. Since the digital acoustic signal reproduced by the acoustic signal recording medium 11 by the acoustic signal reproducing means 12 is a signal having polarity, it is made non-polar by using the absolute value converting means 13 and is a signal indicating the magnitude of the signal in real time. Convert the absolute value so that. This absolute-value-converted signal has a short time constant determined by the processing of the synchronization timing one synchronization time before.
3 or longer than the result of the digital filter calculating means 24 having a long time constant, the amplitude increase / decrease judging means 21 judges that the signal amplitude tends to increase, and converts the absolute value into a low pass filter or a differential filter having a short time constant. The switching means 22 is switched to the input side of the digital filter computing means 23 having a short time constant so as to input the generated signal, and the signal is rapidly increased. On the other hand, when it is smaller than the synchronization timing processing result one synchronization time before, it is determined that the signal amplitude tends to decrease, and the switching means 22 is switched to the digital filter arithmetic means 24 side with a long time constant to loosen the filter arithmetic result. Reduce. Since the result of these filter operations is an amplitude signal output indicating the average amplitude of the input acoustic signal, the dynamic range compression coefficient corresponding to this amplitude is calculated using the dynamic range compression coefficient calculation means 15, and this coefficient is calculated. And the digital audio signal having the above polarity are multiplied, sent to the digital-analog conversion means 18, converted into an analog signal, and converted into sound by the audio speaker 19. When the input sound signal level detected using the sound signal reproducing means 12 suddenly increases in this way, the amplitude increase / decrease judging means 21, the switching means 22, the digital filter calculating means 23 with a short time constant, and the dynamic range compression coefficient calculation. By rapidly reducing the compression coefficient by using the means (15), the dynamic characteristics of the acoustic signal dynamic range compression device are improved, and the psychological sway of the listener can be alleviated.

FIG. 6 shows the input / output characteristics of the acoustic signal dynamic range compression apparatus of the second embodiment, that is, the processing calculated using the digital acoustic signal detected by the acoustic signal reproducing means 12 and the multiplying means 17. The correspondence of the dynamic range of the subsequent output signal is shown. This correspondence is related by the following equation, where x is the amplitude of the input acoustic signal and y is the level of the output acoustic signal.

Y = (x / 10) ^{0.5 From} this, the compression coefficient calculated by the dynamic range compression coefficient calculation means 15 of FIG. 5 is given by the compression coefficient = 1 / (10 × x) ^0.5 .

The compression coefficient is calculated in advance discretely and RO
Prepare as M table. FIG. 7 shows a processing flow chart of the embodiment of the present invention. In FIG. 7, 31 is a process of waiting for the synchronization timing, and 32 is a process of inputting the input acoustic signal (A _n ) detected by the acoustic signal reproducing means 12 of FIG. Note that n is a subscript indicating n time,
When the synchronization timing period is dT, time = n × dT. 33 is a process for converting an absolute value, 34 is a process for judging whether the signal is in an increasing tendency or a decreasing tendency, and branches to processings 35 and 36, respectively. 37 is a process for calculating the dynamic range compression coefficient CR _n using C _n , 38 is a process for performing a product operation of the dynamic range compression coefficient CR _n and the input acoustic signal, and 39 is a process 3
The result D _n of the product operation of 8 is output, and the process returns to the synchronization timing waiting process 31. It is assumed that the above processing is repeated at each synchronization timing. Reference numeral 35 is a digital filter operation having a short time constant with B _n as an input,
36 is a digital low-pass filter operation having a long time constant with B _n as an input, and the operation result is C _n .
^{_{C n = (1-2 -p) ×}} C n-1 +2 -p × B n The C _n = (1-2 Specific example of calculation of filter operation 36 Specific example of calculation of filter operation 35 ^{- q} ) × C _n-1 +2 ^−q × B _n . If the synchronization timing period is assumed to be 22.7 μs, p and q should be 2 and 8 respectively in order to set the filter time constant in the filter calculation 35 to about 1.5 KHz and the filter time constant in the filter calculation 36 to about 24 KHz. Good. If p is set small, for example, to 0, peak hold operation is performed, and p is set to a negative value, for example, -1.
If it becomes, it will be a differential filter that can expect the prediction effect,
When the amplitude is increasing, the filter result is updated in real time or with a predicted value.

[0022]

EFFECT OF THE INVENTION (Effect 1) As is apparent from the first embodiment of the present invention, when an acoustic signal of a low frequency having a possibility that the time variation of the dynamic range compression coefficient becomes large is input. Also in the above, there is an effect that the dynamic characteristics are improved while suppressing the deterioration of the distortion rate of the acoustic signal dynamic range compression device, and the mental agitation of the listener can be alleviated.

(Effect 2) As is apparent from the second embodiment of the present invention, when the input acoustic signal tends to increase, the compression coefficient is rapidly reduced, and when the input acoustic signal tends to decrease. By switching the digital low-pass filter so as to slowly increase the compression coefficient, the amount of fluctuation of the compression coefficient is suppressed, a suddenly generated large acoustic signal is rapidly compressed, and the emotional sway of the listener can be eased. Has the effect.

[Brief description of drawings]

FIG. 1 is a block diagram of an acoustic signal dynamic range compression apparatus according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing the processing of the same acoustic signal dynamic range compression apparatus.

FIG. 3 is a flowchart showing an example of processing for determining the magnitude of the instantaneous amplitude level of an input acoustic signal.

FIG. 4 is a flowchart showing another example of the processing for determining the magnitude of the instantaneous amplitude level of the input acoustic signal.

FIG. 5 is a block diagram of an acoustic signal dynamic range compression device according to a second embodiment of the present invention.

FIG. 6 is a diagram showing input / output characteristics of the same acoustic signal dynamic range compression device.

FIG. 7 is a flowchart showing the processing of the same acoustic signal dynamic range compression apparatus.

FIG. 8 is a block diagram of a conventional acoustic signal dynamic range compression device.

[Explanation of symbols]

 11 acoustic information recording medium 12 acoustic signal reproducing means 13 absolute value converting means 14 signal amplitude detecting means 15 dynamic range compression coefficient calculating means 16 compression coefficient switching means 17 multiplying means 18 digital / analog converting means 19 acoustic speaker 110 synchronization timing signal

Claims (2)

[Claims] 1. An absolute value converting means for calculating the magnitude of a digital audio signal having a polarity, and a signal for detecting an average amplitude of the acoustic signal using the signal converted by the absolute value converting means. Amplitude detection means, dynamic range compression coefficient calculation means for momentarily calculating a dynamic range compression coefficient corresponding to the signal amplitude detected by the signal amplitude detection means, and the acoustic signal and the dynamic range compression coefficient are multiplied. The output of the input acoustic signal is provided with a multiplication means for outputting the result as an output acoustic signal, and a compression coefficient switching means for switching the dynamic range compression coefficient only when the instantaneous amplitude level of the acoustic signal becomes small. When the amplitude level is large, the compression coefficient calculated at that time is not used, and the compression coefficient switching unit switches the compression coefficient last time. By holding the compression coefficient, even in the case of an input signal of a frequency in which the variation of the compression coefficient is large, a large level acoustic signal is rapidly reduced without deteriorating the distortion rate of the output acoustic signal. Sound signal dynamic range compression device. 2. An absolute value conversion means for calculating the magnitude of a digital audio signal having a polarity, and an amplitude increase / decrease judgment for judging whether the signal converted by the absolute value conversion means is increasing or decreasing. Means for correcting the smoothing filter calculation result in the direction in which the amplitude increases in accordance with the output of the amplitude increase / decrease determination means or in the direction in which the signal amplitude decreases in accordance with the prediction operation. A signal amplitude detecting means for switching between smoothing filters having different time constants depending on the direction of change of the signal amplitude so as to correct the result, and a dynamic range compression coefficient corresponding to the signal amplitude detected by the signal amplitude detecting means is calculated moment by moment. And a dynamic range compression coefficient calculating means for multiplying the acoustic signal and the dynamic range compression coefficient, and outputting the result as an output acoustic signal. When the amplitude of the input acoustic signal is increased, the dynamic range compression coefficient is rapidly updated when the amplitude of the input acoustic signal is increased, thereby rapidly reducing a large-scale acoustic signal that occurs suddenly. An acoustic signal dynamic range compression device characterized by slowly increasing an output acoustic signal when decreasing.