JP3037002B2 - Signal processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing apparatus for an audio device or the like, and more particularly to a signal processing apparatus for changing processing according to the level of an input signal.

[0002]

2. Description of the Related Art With the advance of digital processing technology, digital processing has been adopted in various fields, and digital processing has also been adopted in audio equipment.

On the other hand, in the processing of an audio signal, there are various cases where the content of the processing must be changed according to the level of the input signal. For example, a dynamic range compressor in an audio amplifier has an input level of 0
The input signal is output as it is at dB, and the input level is -60.
The input signal is increased by 6 dB at dB and output, and 0 dB to-
At 60 dB, the gain amount is continuously changed so that the output from the audio device is easy to hear.

[0004] Such a change in the gain of the compressor changes the following state according to the change state of the input signal. That is, when the input signal largely changes from a low level to a high level (at the time of an attack), the tracking is accelerated, and when the input signal changes from a high level to a low level (at the time of release), the tracking is slowed. I have.

[0005] In addition, during an attack, the following speed is increased as the fluctuation amount of the input signal level increases. In the case of following the input level fluctuation in an analog manner, it can be achieved by connecting a diode in parallel to the resistor of the integrating circuit including the resistor and the capacitor.

On the other hand, in order to obtain such characteristics in a digital circuit, a plurality of low-pass filters having different time constants are prepared, and switching is performed in accordance with the amount of change in the input level.

[0007]

However, such a low-pass filter switching process is complicated and has various problems. That is, DSP (digital signal
When such processing is performed by the processor, there is a problem that the program becomes long and a table for setting the time constant of the low-pass filter becomes large. Further, since the number of time constants is limited, there is a problem that the time constant cannot be changed smoothly, and switching noise occurs when the coefficient is switched.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a signal processing apparatus for changing the signal processing of an input signal in accordance with the level of the input signal.
Bell detector and the input level detector
Changes with the time constant according to the change of the input level from the input level
Time constant control unit for generating a control signal
Mainly processes input signals according to control signals from the control unit
A signal processing unit, wherein the time constant control unit
First integrating circuit for integrating the obtained signal level with a first time constant
And integrating the detected signal level with a second time constant
A second integrator and both of the first and second integrators;
The detected signal level is calculated using a time constant based on the output difference.
And a third integration circuit for integrating, and an output of the third integration circuit
And the control signal is obtained .

[0009]

As described above, the time constant of the third integration circuit is controlled based on the outputs of the first and second integration circuits having different time constants.
I do. Then, based on the output of the third integration circuit,
A control signal for controlling the signal processing of the in-signal processing circuit is obtained.
You. Therefore, the control signal corresponding to the level change of the input signal
Can be obtained, and desired signal processing can be performed using the control signal . Especially in digital processing
The time constant can be continuously converted by a simple circuit.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of the embodiment. An input level detector 10 for detecting the level of an input signal, and a time constant corresponding to a change in the input level from the input level detected by the input level detector 10 are shown. It comprises a time constant control unit 20 for generating a control signal to respond to and a main signal processing unit 30 for processing an input signal according to a control signal from the time constant control unit 20.

The input level detecting section 10 includes an absolute value circuit 1
2, consisting of an integrating circuit 14, a logarithmic conversion circuit 16,
An absolute value of the input signal is integrated and logarithmically converted to output an input level signal corresponding to the amplitude of the input signal.

The time constant control section 20 basically comprises a first integration circuit 21, a second integration circuit 22, a subtracter 23, an absolute value circuit 24, and a third integration circuit 25, which have different time constants. The difference between the outputs of the first and second integration circuits 21 and 22 is calculated by a subtractor 23, and the time constant of the third integration circuit 25 is controlled according to the absolute value of the result of the subtraction. Then, the output of the third integration circuit 25 whose time constant has been determined in this way is output as a control signal.

The main signal processing section 30 is, for example, a compressor that performs dynamic range compression processing on an input signal, and changes the content of the compression processing according to a control signal.

FIG. 2 shows a specific configuration of the time constant control unit 20. Thus, the first to third integration circuits 21, 22, 25
Are each composed of a primary IIR low-pass filter. That is, the input signal is input to the adder b via the coefficient multiplier a, and is also input to the adder b via the delay circuit c and the coefficient multiplier d. The output of the adder b is fed back to the adder b via the delay circuit e and the coefficient multiplier f. The time constant of each integration (low-pass filter) is set by setting the coefficients α, β, and γ to be multiplied in the coefficient multipliers a, d, and f in each integration circuit.

That is, the coefficients α, β, γ of each integration circuit
Is set in the relationship of α = β, γ = 1-2α, and 0 <α <1.

When α is close to 0, the time constant is large,
When it is close to 1, the time constant is small. Therefore, the first integration circuit 21
Is set to be larger (closer to 1) than the coefficient α of the second integration circuit 22 when the input level rises in a stepwise manner as shown in FIG. Output rises relatively quickly, and the output of the second integration circuit 22 rises slowly. Then, by taking the difference between the two in the subtractor 23, a waveform whose value once rises and then returns to 0 with respect to the step-like rising can be obtained.

Here, the output of the subtractor 23 has a rising amount corresponding to a change in the level of the input. Therefore, if the time constant of the third integration circuit 25 is changed using the output of the subtracter 23, integration (low-pass filter) with a time constant according to the level change amount of the input signal can be achieved. Note that the absolute value circuit 24 obtains a positive value even at the time of release, and performs time constant control using this value.

In order to control the time constant of the third integration circuit 25, the coefficient a of the coefficient multiplier may be changed according to the output of the absolute value circuit 24. However, since the output of the absolute value circuit 24 does not always take a value of 0 to 1, a coefficient multiplier 26 for multiplying the coefficient k is provided as shown in FIG. 2 to adjust the magnitude of the value. .
The output α of the coefficient multiplier 26 is used as the third integration circuit 2
5 to two coefficient multipliers a, d,
By supplying the coefficient to another coefficient multiplier f via the 1-kα arithmetic unit 27, the third integration circuit 25 has a small time constant when the change amount of the input signal is large and a small time constant when the change amount of the input signal is small. The constant increases. Thus, the output of the third integration circuit 25 is an input level detection signal that corresponds to the magnitude of the input signal, and follows quickly when the change amount of the level signal is large, and slowly follows when the change amount is small. .

Therefore, the output of the third integrating circuit 25 is supplied to the main signal processing section 30 as a control signal, and the dynamic range is compressed in accordance with the control signal. A compression process can be performed.

In the dynamic range compression processing, as described in the conventional example, the input signal level is 0 dB, the input signal is output as it is, and the input level is -6.
At 0 dB, the input signal is increased by 6 dB and output.
At −60 dB, the gain amount is continuously changed, and the gain is adjusted according to the change in the input.

Further, according to the present embodiment, the first integrating circuit 2
By changing the time constant of the first and second integrating circuits 22 or changing the coefficient of the coefficient multiplier 26, the change width of the time constant in the third integrating circuit 25 can be easily changed. Therefore, various adjustments can be performed very easily.

Further, the time constant at the time of the attack is changed in accordance with the change amount of the input level. When the time constant at the time of the release is fixed to one relatively long time constant, the above-described absolute value circuit 24 is used instead. It is preferable to provide a threshold circuit. That is, as shown in FIG. 4, when the output from the subtractor 23 is equal to or smaller than a certain value, the predetermined threshold value is fixed. In this case, in the case of release, the output of the subtractor 23 becomes negative.
The time constant is always equal to or smaller than the threshold, and the time constant is set to the threshold. Therefore, the time constant at the time of release of the third integration circuit 25 can be fixed to one time constant, and at the time of an attack, the time constant changes in accordance with the amount of change in the input level as described above.

As described above, according to the present embodiment, in the digital circuit, the input signal level can be detected with a time constant corresponding to the change amount of the input signal, and desired signal processing is performed using this level signal. be able to. Needless to say, it can be used in other signal processing if such characteristics are required.

[0024]

As described above, according to the signal processing device of the present invention, in digital signal processing, level detection can be performed with a time constant corresponding to the amount of change in the input signal level. , Suitable signal processing can be performed. In particular, the time constant can be continuously converted by a simple circuit.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment.

FIG. 2 is a block diagram showing a configuration of a time constant control unit 20.

FIG. 3 is an explanatory diagram showing waveforms of respective units.

FIG. 4 is an explanatory diagram of processing by threshold setting.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Input level detection part 20 Time constant control part 30 Main signal processing part

Claims (1)

(57) [Claims] 1. A signal processing apparatus for changing in accordance with the level of the input signal a signal process on the input signal, the input level detector for detecting the level of the input signal, the input level detected in the input level detector
A control signal that changes with a time constant corresponding to the input level
A time constant control unit to be generated, and an input signal processed in accordance with a control signal from the time constant control unit.
A time signal control unit , wherein the time constant control unit integrates the detected signal level with a first time constant.
An integrating circuit for integrating the detected signal level with a second time constant;
An integrating circuit, based on the difference between the outputs of both the first and second integration circuits
Third integration for integrating the detected signal level with a time constant
It includes a circuit, a signal processing apparatus characterized by obtaining the control signal to the output of the third integrating circuit.