KR960011409B1 - Automatic gain control system for voice signal - Google Patents

Abstract

an analog/digital converter converting voice signal to a digital value; an electronic controlled variable attenuator installed on the front side of the analog/digital converter; a reading means reading the output voltage of the electronic controlled variable attenuator periodically; a comparing means outputting a detection deviation by comparing the read output voltage with a reference level; and an attenuation rate setting means changing the attenuation rate by setting the attack time and the recovery time according to the detection deviation.

Description

Voice signal automatic amplitude control device

1 is a block diagram of one embodiment of the automatic audio signal control apparatus of the present invention.

2 is a block diagram of another embodiment of the audio signal automatic amplitude control apparatus of the present invention.

FIG. 3 is a flow chart illustrating the operation of the attenuator 8 of FIG.

4 is a flowchart for explaining the overall operation of the control device in FIG.

FIG. 5 is another flowchart illustrating the overall operation of the controller of FIG.

FIG. 6 is a flowchart for explaining the operation when increasing the attenuation amount of the electron volume in FIG. 1 and FIG.

FIG. 7 is a flowchart for explaining the operation when returning the attenuation amount of the significant electron volume in FIG. 1 and FIG.

FIG. 8 is another flowchart for explaining the operation when returning the attenuation amount of the significant electron volume in FIG. 1 and FIG.

9 is a graph showing the relationship between the recovery time set by the flowcharts of FIGS. 7 and 8 and the amount of attenuation.

10 is a block diagram of an automatic audio signal amplitude control device using a conventional passive variable attenuator.

11 is a block diagram of a voice signal automatic amplitude control apparatus using a variable attenuator by a conventional transistor.

* Explanation of symbols for main parts of the drawings

1: Electronic Volume 2: Low Pass Filter

3: analog / digital converter 4: digital signal processor

5: Digital / Analog Converter 6: Input Terminal

7: output terminal 8: attenuator

11: Micom 12: Analog-to-digital converter

13 read means 14 comparison means

15: reference value 16: ATT value setting means

17: comparison means 18: reference value

19: detection deviation 20: attenuation rate setting means

The present invention relates to a voice signal automatic amplitude control apparatus for electronically controlling the input signal level of an analog / digital (A / D) converter for converting a voice signal from an analog value to a digital value.

In the analog / digital converter, when the level of the input analog audio signal becomes higher than the maximum allowable level of the analog / digital converter, it becomes impossible to faithfully convert the level of the original analog audio signal into a digital signal. For this reason, a variable attenuator is provided in front of the analog / digital converter, and the signal distortion is reduced by controlling the input level of the analog / digital converter within a predetermined level range.

On the contrary, when the input level of the analog audio signal is low, the attenuation amount of the variable attenuator is reduced to increase the signal level input to the analog / digital converter to improve the signal-to-noise (S / N) ratio.

And when changing the attenuation of this variable attenuator, it is necessary to make the level change of the audio signal sound natural to the person listening to the reproduced sound. To this end, when a large-level audio signal is input, the attenuation amount increased by decreasing the level of the input audio signal so that the allowable time (attack time) until the attenuation is increased to attenuate the audio signal to the allowable level is shortened. It is necessary to operate so that the response time (recovery time) until the return to the original is delayed.

An example of a conventional variable attenuator will be described with reference to the drawings.

10 shows a voice signal automatic amplitude control apparatus using a passive variable attenuator 21. As shown in FIG. The variable attenuator 21, the low pass filter 2, the analog / digital converter 3, the digital signal processor 4, and the digital / analog converter 5 are disposed between the input terminal 6 and the output terminal 7; Connect.

The audio signal input from the input terminal 6 is attenuated by a predetermined amount by the variable attenuator 21, and is converted by the analog / digital converter 3 into an analog signal to a digital signal. The converted digital signal is signal processed by the digital signal processor 4 and then converted into an analog signal by the digital / analog converter 5 and output to the output terminal 7.

When the input analog audio signal exceeds the maximum allowable level of the analog / digital converter 3, the variable attenuator 21 is manually adjusted to increase the attenuation amount, and the signal level input to the analog / digital converter 3 is adjusted. It is suppressed within the allowable level. This reduces the distortion of the audio signal.

In addition, when the input audio signal is small, the attenuation amount of the variable attenuator 21 is manually reduced and the signal level input to the analog / digital converter 3 is increased. This improves the S / N ratio of the audio signal.

In this manual variable attenuator 21, the attack time and recovery time can be adjusted by changing the speed of manual operation.

However, in the case where the passive variable attenuator 21 is used, the signal source when the level difference between the audio signal signal sources input to the analog / digital converter 3 is large, or when the level maximum value and the minimum value are significantly different from each other. Operation is cumbersome as you need to make manual adjustments when you change the speed or when the input signal level changes.

Next, an example of the audio signal automatic amplitude control apparatus using the automatic variable attenuator by the transistor will be described with reference to FIG. Here, only the differences from the above-described FIG. 10 will be described.

In this example, the collector and emitter of the transistor 22 are connected between the input terminal 6 and ground as a variable attenuator. The resistance between the collector and the emitter of the transistor 22 becomes smaller when the voltage applied to the base increases, and when the voltage applied to the base decreases, the resistance increases.

When the audio signal level input to the analog / digital converter 3 increases, the voltage value applied to the base of the transistor 22 increases, and the resistance value between the collector and the emitter decreases. As a result, the resistance value between the input terminal 6 and ground decreases, and the amount of attenuation by the transistor 22 increases.

Conversely, when the audio signal level input to the analog / digital converter 3 decreases, the resistance of the transistor 22 increases, and the amount of attenuation by the transistor 22 decreases. As a result, the attenuation amount by the variable attenuator changes in accordance with the audio signal level input to the analog / digital converter 3, and the attenuation amount by the variable attenuator changes according to the audio signal level input to the analog / digital converter 3, The level of the audio signal input to the digital converter 3 automatically becomes a value within the allowable range.

The attack time T1 of this variable attenuator is determined by the number of viewpoints of the resistor R1 and the capacitor C1 as follows.

The recovery time T2 is determined by the time constant of the resistor R2 and the capacitor C1 as follows.

The variable attenuator using the transistor 22 described above can automatically control the amplitude of the audio signal input to the analog-to-digital converter 3, and the ETEK time and the recovery time are the resistance R1 of the time constant circuit as described above. , R2) and the capacitor C1 can be set in advance by setting the values.

However, the range that can be controlled by the variable attenuator using this transistor is as small as 15-20 dB. For this reason, it is not possible to automatically control an audio signal having a wide range of levels, such as a microphone input, over the entire range of varying levels.

In addition, since the attack time and recovery time are fixed by the values of the resistor and the capacitor, it is difficult to change the set value.

The conventional variable attenuator described above has a problem that the manual variable attenuator is cumbersome to operate. In addition, the variable attenuator using a transistor has a problem that the signal is distorted when the input signal is greatly changed, and there is a problem that the attack time and recovery time cannot be freely adjusted. The present invention is intended to solve these problems.

According to the present invention, in the automatic audio signal control apparatus, the attenuation amount of the variable attenuator is automatically changed in accordance with the level of the analog audio signal to be input, so that even if the level of the input analog audio signal varies greatly, The purpose is to keep the level within a predetermined range.

It is also an object of the present invention to change the attack time and recovery time of the variable attenuator according to the level of the input signal of the analog / digital converter, and furthermore, to freely control the setting of the attack time and recovery time.

The present invention provides an electronic control variable attenuator in front of an analog / digital converter for converting an analog voice signal into a digital signal in order to achieve the electrical object. Reading means for reading the output level of the electronic control variable attenuator at regular intervals, comparison means for outputting the detection deviation by comparing the read output level with a reference level, and when the detection deviation is detected, A sound signal automatic amplitude control apparatus is constituted by attenuation rate setting means for setting an attack time and a recovery time to change the attenuation rate of the electronic control variable attenuator.

According to the above means, the electronic control variable attenuator automatically changes the attenuation amount of the variable attenuator according to the level of the input analog audio signal, so that even if the level of the analog audio signal varies greatly, The level can be maintained within a predetermined range.

In addition, since the attack time and recovery time of the variable attenuator change depending on the level of the input signal of the analog / digital converter, even if the attenuation amount of the variable attenuator is changed, it is possible to make a natural sense sound when listening to the reproduced sound. For this reason, the allowable input level of the audio signal input to the variable attenuator can be made large.

In addition, the setting of the attack time and recovery time of the variable attenuator can be freely changed.

An embodiment of the present invention will be described with reference to the drawings.

1 and 2 are block diagrams of embodiments of the present invention. In the figure, the electronic volume 1, the low pass filter 2, the analog / digital converter 3, the digital signal processor 4, and the digital / analog converter 5 are provided with an input terminal 6 and an output terminal ( 7) is connected between.

The analog audio signal input from the input terminal 6 is attenuated by the electronic volume 1 by a predetermined amount and input to the low pass filter 2. The amount of attenuation of the electronic volume 1 at the time of power supply is set to -6 dB.

The low pass filter 2 is an antiarea filter, and the analog audio signal is attenuated by the low pass filter 2 so as to pass only the reproduction signal frequency and input to the analog / digital converter 3.

The analog / digital converter 3 converts an analog signal into a digital signal. The converted digital signal is subjected to signal processing by the digital signal processor 4, and then converted into an analog signal by the digital / analog converter 5 and output to the output terminal 7.

Next, the control circuit shown in FIG. 1 is demonstrated using the flowchart of FIGS. 3-8.

The output of the electron volume 1 is input to the microcomputer 11. The analog / digital converter 12 in the microcomputer 11 must maintain its input level within a certain value of, for example, 5V maximum. Therefore, the output of the electron volume 1 is input to the microcomputer 11 via the attenuator 8.

The microcomputer 11 reads the output of the attenuator 8 at predetermined cycles. In this microcomputer 11, the sampling frequency is set to twice or more than the cutoff frequency of the low pass filter 2.

The input level of the analog-to-digital converter 12 of the microcomputer 11 is converted into a digital signal and read by the reading means 13. The input / output level is compared with the reference value 15 by the comparison means 14. The comparison result is input to the ATT value setting means 16, and the ATT value set here is input to the attenuator 7 and the attenuation rate setting means 20 described later.

The attenuation rate setting operation of the attenuator 8 described above will be described using the flowchart of FIG.

When the power is turned on in step S11, the electron volume 1 is initially set to -6 dB in step S12, and the attenuator 8 is initially set to -10 dB in step S13.

In step S14, the input level of the analog-to-digital converter 12 is compared with the reference value 15V, and if the input level is less than or equal to the reference value, the process returns to step S13. That is, if the input level of the analog-to-digital converter 12 is 5 V or less, the set value of the attenuator 8 is fixed to the initially set value (−10 dB).

If it is determined in step S14 that the input level exceeds the reference value, the flow advances to step S15 to increase the attenuation amount of the attenuator 8 by -1 dB by the ATT value setting means 16. The steps S14 to S15 are repeated until the input level of the analog / digital converter 12 is equal to or less than the reference value, so that the input level of the analog / digital converter 12 is kept below 5V. As a result, the input of the attenuator 8 is always maintained at a level below the maximum allowable level.

The value of the reading means 13 in FIG. 1 is also compared with the reference value 18 by the comparing means 17, so that the detection deviation 19 between the reading value and the reference value difference is input to the attenuation rate setting means 20. FIG. The operation of the damping rate setting means 20 will be described using the flowcharts of FIG. 4 and FIG.

When the power is turned on in step S21, the electronic volume 1 is initially set to -6 dB in step S22, and the input level to the analog-to-digital converter 12 becomes 5 V or less of the maximum allowable level. In S23, the detection deviation 19 is compared with the setting deviation R4.

When the input level exceeds the maximum allowable level of the analog / digital converter 3, if the detection deviation 19 exceeds the setting deviation R4, the flow proceeds to step S31 of FIG. If the detection deviation 19 is below the reference deviation R4, it progresses to step S24 demonstrated next.

In step S24, the input deviation of the analog / digital converter 12 is obtained using the detection deviation 19 and the reference value 18 every three minutes, and the maximum value of the input level of the analog / digital converter 12 is -3 dB or less. It is determined whether or not the average value is -13 dB or less. If the input level is a proper value, it is NO, and the flow returns to step S23, where the set value of the attenuator 8 does not change.

If the input level of the analog / digital converter 12 is small, the determination result of step S24 is yes (YES), and the flow proceeds to step S25. If the process proceeds after this step S25, the attenuation amount of the electronic volume 1 is reduced to increase the S / N ratio, and the input level of the analog / digital converter 3 is increased. In step S25, the attenuation amount of the electron volume 1 is reduced by 1 dB.

Subsequently, in step S26, it is determined whether or not the input level of the analog-to-digital converter 12 is a maximum value of −3 dB or less, or an average value of −13 dB or less every one minute. If NO, the input level of the analog-to-digital converter 3 is of a suitable property, and the flow returns to step S23. In the case of YES, the flow returns to step S25 through step S27, and decreases the amount of attenuation of the electron volume 1 by 1 dB. As a result, when the input level reaches the created value, the flow returns to step S23 from step S26. If the amount of attenuation of the electron volume 1 is zero, the amount of attenuation can not be stored more than this, and the flow returns to step S25.

By repeating the subphase, the input level of the analog-to-digital converter 3 is increased to an appropriate level. This improves the S / N ratio.

Next, the operation when the input level exceeds the maximum allowable level of the analog / digital converter 3 and it is determined in step S23 of FIG. 4 that the detection deviation 19 is greater than the reference deviation R4 is determined. Explain using 6 degrees.

In the flowchart of FIG. 6, the reference deviation is set to R1 at +10 dB, R2 at +5 dB, R3 at +2 dB, and R4 at +1 dB to -∞.

Steps S31 to S35 determine whether the level of the detection deviation 19 corresponds to which reference deviation range, and the process proceeds to steps S36 to S39 corresponding to the corresponding steps S31 to S34. In steps S36 to S39, the amount of attenuation determined for each step and its set time are output to the electronic volume 1, and then the process returns to the original steps S31 to S34. At the same time, only the amount of attenuation determined in steps S36 to S39 is also reduced in the detection deviation 19.

Here, as an example, the case where the detection deviation is 19 dB will be described.

Since 19 dB of the detection deviation corresponds to a range of 10 dB or more of the reference deviation R1 of step S31, the flow advances to step S36. Here, the attenuation of the electron volume 1 is attenuated by -10 dB, and the set time is 200 mS. Then, 19dB of the detection deviation is attenuated by -10dB and the process returns to step S31.

Since the detection deviation is 9 dB, step S31 passes and the process shifts to step S37 because it corresponds to the range of 10-5 dB of step S32. Here, the attenuation of the electron volume 1 is attenuated by -5 dB, and its set time is 100 mS. Then, 9 dB of the detection deviation is attenuated by -5 dB and the process returns to step S32.

Since the detection deflection becomes 4 dB, step S32 passes and the process shifts to step S38 because it corresponds to the range of 5-2 dB of step S33. Here, the attenuation of the electron volume 1 is attenuated by -2 dB, and the set time is 50 mS. Then, 4 dB of the detection deviation is attenuated by -2 dB and the process returns to step S33.

Since the detection deviation is 2 dB, the process shifts from step S33 to step S38 again. Here again, the attenuation of the electron volume 1 is attenuated by -2 dB, and its set time is 50 mS. Then, 2dB of the detection deviation is attenuated by -2dB and the process returns to step S38.

Since the detection deviation is 0 dB, the processing passes through steps S33 and S34. Since it corresponds to 1 dB or less of step S35, the operation ends here, and the attenuation amount and attack time of the electron power factor 1 are determined.

As a result of the above operation, the electron volume 1 increases the amount of attenuation by -19 dB corresponding to the detection deviation. The attack time is 200mS + 100mS + 50mS = 400mS.

As described above, the attenuation rate setting means 20 adjusts the amount of attenuation of the electron volume 1 in correspondence with the input analog signal level. The attack time changes according to the deviation of the input signal level.

Also, when the attenuation amount of the attenuator 8 is attenuation amount larger than the normal set value (initial set value -10 dB) as previously described with reference to FIG. 3, the attenuation rate setting means from the ATT value setting means 16. The correction coefficient is calculated from the ATT set value inputted in (20), and the attenuation amount and attack time are determined using this.

Following. In the state where the attenuation amount of the electronic volume 1 is increased according to the flowchart of the above drawing, the case where the level of the audio signal decreases and the attenuation amount is returned to the original state will be described with reference to Figs.

In this case, the recovery time for returning the amount of attenuation to the original amount is longer than the attack time so that the change in the level of the audio signal is accepted as a natural sense when the audio signal is reproduced. It needs to be operated.

7 and 8 are performed when the amount of attenuation of the electron volume 1 is larger than the initial set value (−60 dB), and the detection deviation 19 becomes (−).

Steps S41 to S49 determine which range the level of the detection deviation 19 corresponds to, and the process moves from the corresponding steps S41 to S49 to the corresponding steps S51 to S59. In steps S51 to S59, a predetermined amount of attenuation is set for each predetermined recovery time until the detection deviation 19 reaches a minimum value of the corresponding range of steps S41 to S49, and the recovery time and the amount of attenuation are set to the electronic volume 1. Output to At the same time, the detection deviation 19 also reduces the predetermined amount of attenuation and advances to the predetermined step. Here, as an example, the case where the detection deviation is -17 dB will be described.

If the detection deviation is -17 dB, it falls within the range of -15-20 dB of step S48, and the flow advances from step S48 to step S58. In step S58, 0.1 dB is set for every 200 mS between a detection deviation of -17 dB to -15 dB of the minimum value of the step S48 range. Therefore, in step S58, the attenuation amount of 2 dB is output to the electronic volume 1 during the recovery time of 4 seconds (at 2 dB / 0.1 dB x 200 mS = 4S), and at the same time, the -17 dB of the detection deviation is also reduced by 2 dB to -15 dB. It becomes

When the process proceeds from step S58 to step S47, the detection deviation is -15 dB, which corresponds to the range of step S47, and moves to step S% In step S57, the detection deviation is stepped from -15 dB. 0.1 dB is set for every 150 mS between 5 dB, which becomes -10 dB of the minimum value of the range (S47), and therefore, at step S57, the amount of attenuation of 5 dB between the recovery time of 7.5 seconds (at 5 dB / 0.1 dB × 150 mS = 7.5 S) is obtained. This electronic volume 1 is output to the electronic volume 1, and at the same time, the detection deviation of -15 dB is also reduced by 5 dB to -10 dB.

Returning from step S57 to step S46, the detection deviation is -10 dB, so that the detection deviation moves to step S56 corresponding to the step S46 range. In step S56, 0.1 dB is set every 100 mS between 5 dB at which the detection deviation is -10 dB to the minimum value -5 dB of the step S46 range. Therefore, in step S56, a reduction amount of 5 dB is output to the electronic volume 1 between the recovery time of 5 seconds (at 5 dB / 0.1 dB x 100 mS = 5S), and at the same time, the -10 dB of the detection deviation is also reduced by 5 dB to -5 dB. It becomes

The operation is repeated as described above, and finally the operation ends in step S51. As a result, the recovery time is set at 0.9 seconds in step S55, 1.0 seconds in step S54, 1.2 seconds in step S53, 1.5 seconds in step S52, and 2.0 seconds in step S51. The entire recovery time is 4 + 7.5 + 5 + 0.9 + 1.0 + 1.2 + 1.5 + 2.0 = 23.1 seconds, during which the attenuation of the electron volume 1 changes as shown in FIG. 9 and returns to the original attenuation amount. .

9 shows a case where the detection deviation 19 is -17 dB, and a case of -2 dB, -7 dB, and -12 dB. In the case where the value of the detection deviation 19 is any other value, the same operation as described above is performed, and the amount of attenuation changes as the time shown in FIG.

As shown in this graph, when the amount of attenuation is large, the recovery time is set longer than when it is small, and when the audio signal is reproduced, it is possible to be taken as a natural sense.

In addition, the setting of the attack time and recovery time can be easily changed by changing the numerical value shown in the flowchart of FIG. 6 thru | or 8 in the damping rate setting means 20. FIG.

According to the present invention, in the automatic audio signal amplitude control apparatus, the attenuation amount of the variable attenuator can be automatically changed according to the level of the input analog audio signal, and even if the level of the input audio signal fluctuates greatly, It can be kept within range.

According to the present invention, the attack time and recovery time of the variable attenuator can be changed in accordance with the level of the input signal of the analog / digital converter, and the response characteristics of the attack time and recovery time of the variable attenuator can be freely controlled. .

Claims (2)

Analog-to-digital converter for converting audio signals to digital values, Electronic control variable attenuator installed in front of the analog / digital converter, Readout means for reading the output voltage of the previous control variable attenuator at regular intervals, The read output voltage Comparison means for outputting a level deviation from the reference level and a comparison term, and attenuation rate setting means for changing the attenuation rate of the electronic control variable attenuator by setting the attack time and recovery time according to the detection deviation when the detection deviation is detected. Voice signal automatic amplitude control device, characterized in that. The analog / digital converter according to claim 1, wherein an analog / digital converter is provided in front of the reading means, and an attenuator for attenuating the input level of the analog / digital converter to a level below the allowable value when the input level exceeds the maximum allowable value. Automatic audio signal amplitude control device, characterized in that installed in the front of the.