JPH06314942A - Automatic amplitude limiter for voice signal - Google Patents

Abstract

PURPOSE: To hold the attenuation volume within a given range even when the level of the voice signal to be inputted is greatly varied in a voice signal automatic amplitude controller by automatically varying attenuation volume of a variable attenuator according to a level of a voice signal inputted in an A/D converter. CONSTITUTION: An electronic control variable attenuator 8 is provided at a front stage of the A/D converter 12 to convert the voice signal into a digital value. The voice signal automatic amplitude controller is constituted by being provided with a reading means 13 to read an output level of the electronic control variable attenuator 8 by the fixed cycle, a comparison means 17 to output a detection deviation 19 by comparing the read output level with a reference level 18 and an attenuation factor setting means 20 to change an attenuation factor of the electronic control variable attenuator 8 by setting attack time and recovery time according to the detection deviation when the detection deviation is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice signal automatic amplitude control apparatus for electronically controlling an input signal level of an A / D converter for converting a voice signal from an analog value to a digital value.

[0002]

2. Description of the Related Art The A / D converter can faithfully convert an original analog audio signal into a digital signal when the level of the input analog audio signal exceeds a maximum allowable level of the A / D converter. It will be impossible. Therefore, A / D
A variable attenuator is provided in front of the converter, and the input level of the A / D converter is controlled within a predetermined level range to reduce signal distortion.

On the contrary, when the input level of the analog audio signal is low, the attenuation amount of the variable attenuator is reduced to A /
The S / N ratio is improved by increasing the signal level input to the D converter. When changing the amount of attenuation of the variable attenuator, it is necessary for the person who hears the reproduced sound to receive a natural change in the level of the audio signal. To this end, when a high level audio signal is input, the response time (attack time) until the attenuation amount is increased and the audio signal is attenuated to an allowable level is shortened so that the level of the input audio signal is reduced. It is necessary to operate so that the response time (recovery time) until the increased attenuation amount is returned to the original value is delayed.

An example of a conventional variable attenuator will be described with reference to the drawings. FIG. 10 shows an audio signal automatic amplitude control apparatus using a manual variable attenuator 21. Variable attenuator 21, low-pass filter (anti-alias filter) 2, A / D converter 3, digital signal processor 4, D / A converter 5
Is connected between the input terminal 6 and the output terminal 7.

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

When the input analog audio signal exceeds the maximum allowable level of the input of the A / D converter 3, the variable attenuator 21 is manually adjusted to increase the amount of attenuation, and the A / D converter 3 receives it. Keep the input signal level within the allowable level. This reduces distortion of the audio signal. Also,
When the input audio signal is small, the attenuation amount of the variable attenuator 21 is manually decreased to increase the signal level input to the A / D converter 3. 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, when this manual variable attenuator 21 is used, the level difference between the signal sources of the audio signals input to the A / D converter 3 is large, or the maximum and minimum levels are significantly different. In the case of a signal source, the operation becomes complicated because it is necessary to make a manual adjustment each time the signal source is changed or the input signal level changes.

Next, an example of an automatic audio signal amplitude control device using an automatic variable attenuator using a transistor will be described with reference to FIG. Here, only the points different from FIG. 10 will be described. In this example, the collector and the emitter of the transistor 22 are connected between the input terminal 6 and the ground as a variable attenuator. The resistance between the collector and the emitter of the transistor 22 decreases as the voltage applied to the base increases, and increases as the voltage applied to the base decreases.

The analog audio signal taken out from the input of the A / D converter 3 is amplified by the amplifier 23 and rectified by the diodes D1 and D2. This rectified rectified voltage V ₀ is applied to the base of the transistor 22 via a time constant circuit composed of resistors R ₁ and R ₂ and a capacitor C ₁ . With this configuration, when the audio signal level input to the A / D converter 3 increases, the voltage value applied to the base of the transistor 2 increases and the resistance value between the collector and the emitter decreases. As a result, the resistance value between the input terminal 6 and the ground is reduced, and the amount of attenuation by the transistor 22 is increased.

On the contrary, when the audio signal level input to the A / D converter 3 decreases, the resistance of the transistor 22 increases and the amount of attenuation by the transistor 22 decreases.
Thereby, the amount of attenuation by the variable attenuator changes according to the audio signal level input to the A / D converter 3, and the level of the audio signal input to the A / D converter 3 automatically falls within the allowable range. It becomes a value.

The attack time T ₁ of this variable attenuator is determined by the time constant of the resistor R ₁ and the capacitor C ₁ as shown in the following equation. [Equation 1] T ₁ = 2πR ₁ C ₁ × 0.6V ₀ / √2 The recovery time T ₂ is determined by the time constant of the resistor R ₂ and the capacitor C _{1 as in} the following equation.

[Equation 2] T ₂ = 2πR ₂ C _{1 The} variable attenuator using the transistor 22 described above can automatically control the amplitude of the audio signal input to the A / D converter 3. Also, the attack time and the recovery time depend on the resistance R ₁ of the time constant circuit as described above.
It can be set in advance by setting the values of R ₂ and the capacitor C ₁ .

However, the range that can be controlled by the variable attenuator using this transistor is 15 to 20 d.
It is as narrow as B. For this reason, it is not possible to automatically control an audio signal whose level changes in a wide range, such as a microphone input, over the entire range in which the level changes. Furthermore, since the attack time and the recovery time are fixed by the values of the resistor and the capacitor, it is difficult to change the set value.

[0014]

The conventional variable attenuator described above has a problem that the manual variable attenuator is troublesome to operate. Further, the variable attenuator using a transistor has a problem that the signal is distorted when the input signal fluctuates greatly and that the attack time and the 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 amplitude control device, the attenuation amount of the variable attenuator is automatically changed according to the level of the input analog audio signal, and the level of the input analog audio signal is significantly increased. The purpose is to keep the input level of the A / D converter within a predetermined range even if it fluctuates. Further, according to the present invention, the attack time and the recovery time of the variable attenuator can be changed according to the level of the input signal of the A / D converter, and the setting of the attack time and the recovery time can be freely controlled. The purpose is to

[0016]

In order to achieve the above object, the present invention provides an electronically controlled variable attenuator in front of an A / D converter that converts an analog audio signal into a digital signal. Then, reading means for reading the output level of the electronically controlled variable attenuator at regular intervals, comparing means for comparing the read output level with a reference level and outputting a detection deviation, and when the detection deviation is detected,
An audio signal automatic amplitude control device is constituted by the attenuation rate setting means for setting the attack time and the recovery time according to the detection deviation and changing the attenuation rate of the electronically controlled variable attenuator.

[0017]

According to the above means, the electronically controlled variable attenuator automatically changes the attenuation amount of the variable attenuator according to the level of the input analog audio signal, and the level of the analog audio signal fluctuates significantly. However, the level of the analog audio signal input to the A / D converter can be kept within a predetermined range.

Further, since the attack time and the recovery time of the variable attenuator change depending on the level of the input signal of the A / D converter, the reproduced sound can be reproduced even if the attenuation amount of the variable attenuator is changed. The sound can be natural when listening. Therefore, the allowable input level of the audio signal input to the variable attenuator can be increased. Furthermore, the settings of the attack time and recovery time of the variable attenuator can be freely changed.

[0019]

Embodiments of the present invention will be described with reference to the drawings. 1 and 2 are block diagrams of an embodiment of the present invention. In the figure, electronic volume 1, low-pass filter 2, A /
The D converter 3, the digital signal processor 4, and the D / A converter 5 are connected between the input terminal 6 and the output terminal 7.

The analog audio signal input from the input terminal 6 is attenuated by a predetermined amount by the electronic volume 1 and input to the low pass filter 2. When the power is turned on, the attenuation of the electronic volume 1 is set to -6 dB. The low-pass filter 2 is an anti-alias filter, and the analog audio signal is attenuated by the low-pass filter 2 so that only the reproduction signal frequency passes, and input to the A / D converter 3.

The A / D 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, converted into an analog signal by the D / A converter 5, and output from the output terminal 7. Next, the control circuit shown in FIG. 1 will be described with reference to the flowcharts of FIGS.

The output of the electronic volume 1 is input to the microcomputer 11. The input level of the A / D converter 12 in the microcomputer 11 must be kept within a fixed value, for example, 5 V at maximum. Therefore, the output of the electronic volume 1 is input to the microcomputer 11 through the attenuator 8. The microcomputer 11 reads the output of the attenuator 8 at a predetermined cycle.
The sampling frequency of the microcomputer 11 is set to be at least twice the cutoff frequency of the low pass filter 2.

The input level of the A / D converter 12 of the microcomputer 11 is converted into a digital signal and read by the reading means 13. This input 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 8 and the attenuation rate setting means 20 described later.

The operation of setting the attenuation rate of the attenuator 8 described above will be described with reference to the flowchart of FIG. Step S
When the power is turned on in 11, the electronic volume 1 is initialized to -6 dB in step S12, and the attenuator 8 is initialized to -10 dB in step S13.

In step S14, the input level of the A / D converter 12 is compared with the reference value 15 (5V). If the input level is in the normal state below the reference value, the process returns to step S13.
That is, if the input level of the A / D converter 12 is 5 V or less, the set value of the attenuator 8 is the initially set value (-10d).
It is fixed to B). If it is determined in step S14 that the input level exceeds the reference value, the process proceeds to step S15.
The attenuation amount of the attenuator 8 is set to -1 dB by the TT value setting means 16.
To increase. The steps S14 to S15 are repeated until the input level of the A / D converter 12 becomes equal to or lower than the reference value, so that the input level of the A / D converter 12 is maintained at 5V or lower. As a result, the input of the attenuator 8 is always kept below the maximum allowable level.

The value of the reading means 13 in FIG. 1 is further compared with the reference value 18 by the comparing means 17, and the detection deviation 19 of the difference between the reading value and the reference value is input to the attenuation rate setting means 20. The operation of the attenuation rate setting means 20 will be described with reference to the flowcharts of FIGS. The power is turned on in step S21, and the electronic volume 1 is set to -6 in step S22.
After the initial setting to dB, when the input level input to the A / D converter 12 becomes equal to or lower than the maximum allowable level of 5 V, the detection deviation 19 is compared with the setting deviation R ₄ in step S23.

When the input level exceeds the maximum allowable level of the A / D converter 3, and the detection deviation 19 exceeds the set deviation R ₄ , the process proceeds to step S31 in FIG. Detection deviation 1
If 9 is less than the reference deviation R ₄ , the process proceeds to step S24 described below. In step S24, the input level of the A / D converter 12 is obtained using the detection deviation 19 and the reference value 18 every 3 minutes, and the maximum input level of the A / D converter 12 is -3 dB or less. Or not, or the average value is -1
It is determined whether or not it is 3 dB or less. If the input level is an appropriate value, the determination is NO, the process returns to step S23, and the set value of the attenuator 8 does not change.

When the input level of the A / D converter 12 is low, the determination result of step S24 is YES and the process proceeds to step S25. To proceed to step S25 and thereafter,
In order to improve the S / N ratio, the amount of attenuation of the electronic volume 1 is reduced and the input level of the A / D converter 3 is increased. In step S25, the attenuation amount of the electronic volume 1 is reduced by 1 dB.

Next, in step S26, every one minute,
It is determined whether the maximum value of the input level of the A / D converter 12 is -3 dB or less, or whether the average value is -13 dB or less. If NO, the input level of the A / D converter 3 is an appropriate value, and the process returns to step S23. If YES, the process returns to step S25 through step S27 to further reduce the attenuation amount of the electronic volume 1 by 1 dB. As a result, when the input level reaches the appropriate value, the process returns from step S26 to step S23. Also,
When the amount of attenuation of the electronic volume 1 becomes 0, the amount of attenuation cannot be further reduced, and therefore the process returns to step S25.

By repeating the above steps, A
The input level of the / D converter 3 is improved to an appropriate level. This improves the S / N ratio. Next, when the input level exceeds the maximum allowable level of the A / D converter 3, the detection deviation 19 is changed to the reference deviation R _{4 in} step S23 of FIG.
The operation when it is determined to be larger will be described with reference to FIG.

In the flowchart of FIG. 6, reference deviations of R ₁ are +10 dB, R ₂ is +5 dB, and R ₃ is +2 dB.
B and R ₄ are set to +1 dB to −∞. Step S3
1 to 35 determine which reference deviation range the level of the detection deviation 19 corresponds to, and the corresponding steps S31 to S
34 to the corresponding steps 36 to 39. In steps S36 to 39, the attenuation amount and the set time determined for each step are output to the electronic volume 1,
After that, the process returns to the original steps S31 to 34. At the same time,
The level of the detection deviation 19 is also reduced by the attenuation amount determined in steps S36 to 39.

Here, a case where the detection deviation is 19 dB will be described as an example. Since the detection deviation of 19 dB corresponds to the range of 10 dB or more of the reference deviation R ₁ of step S31, the process proceeds to step S36. Here, the attenuation amount of the electronic volume 1 is attenuated by −10 dB, and the set time is set to 200 mS. Then, the detection deviation of 19 dB is −
It attenuates by 10 dB and returns to step S31.

Since the detection deviation is 9 dB, step S3
1 passes and corresponds to the range of 10 to 5 dB in step S32, and therefore the process proceeds to step S37. Here, the amount of attenuation of the electronic volume 1 is attenuated by -5 dB, and the set time is 100 mS. Then, the detection deviation of 9 dB is -5
After attenuation by dB, the process returns to step S42. Detection deviation is 4 dB
Therefore, step S32 is passed and step S33
Since it corresponds to the range of 5 to 2 dB, the process proceeds to step S38. Here, the attenuation amount of the electronic volume 1 is -2d
B is attenuated and the set time is set to 50 mS. Then, the detection deviation of 4 dB is attenuated by -2 dB, and the process returns to step S33.

Since the detection deviation is 2 dB, the process moves from step S33 to step S36 again. Also here, the attenuation amount of the electronic volume 1 is attenuated by -2 dB, and the set time thereof is set to 50 mS. And the detection deviation of 2 dB is -2d
B is attenuated and the process returns to step S33. Since the detection deviation is 0 dB, the process goes through steps S33 and S34. Then, since it corresponds to 1 dB or less in step S35, the operation is ended here, and the attenuation amount and attack time of the electronic volume 1 are determined.

As a result of the above operation, the electronic volume 1 is
The amount of attenuation is increased by −19 dB corresponding to the detection deviation.
And the attack time is 200mS + 100mS
+50 mS + 50 mS = 400 mS. As described above, the attenuation rate setting means 20 adjusts the attenuation amount of the electronic volume 1 according to the input analog signal level. Then, the attack time changes according to the deviation of the input signal level.

The attenuation amount of the attenuator 8 is set to a normal set value (initial set value-
When the attenuation amount is larger than 10 dB), a correction coefficient is calculated from the ATT setting value input from the ATT value setting means 16 to the attenuation rate setting means 20, and the correction coefficient is used to calculate the attenuation amount and the attack time. To decide. Next, a case where the attenuation amount of the electronic volume 1 is increased from the state in which the attenuation amount of the electronic volume 1 is increased and the attenuation amount is returned to the original state will be described with reference to FIGS.

In this case, when the audio signal is reproduced, the recovery time for returning the attenuation amount to the original amount is long depending on the level of the detection deviation so that the change in the level of the audio signal is received with a natural feeling. It is necessary to operate so as to change the length and be longer than the attack time. The operation of the flowcharts of FIGS. 7 and 8 is performed when the attenuation amount of the electronic volume 1 is larger than the initial set value (−60 dB) and the detection deviation 19 becomes (−).

In steps S41 to S49, the detection deviation 19
To which the level of the corresponding level corresponds is determined, and from the corresponding steps S41 to 49 to the corresponding steps S51 to 59.
Move to. In steps S51 to S59, the detection deviation 19
Until a minimum value in the range of the corresponding steps S41 to 49 is set, a predetermined attenuation amount is set for each predetermined recovery time, and the recovery time and the attenuation amount are output to the electronic volume 1. At the same time, the detection deviation 19 also decreases the predetermined attenuation amount and proceeds to a predetermined step.

Here, a case where the detection deviation is -17 dB will be described as an example. If the detection deviation is -17 dB, it corresponds to the range of -15 to -20 dB of step S48. Therefore, steps S48 to S48 are performed.
Move to 58. In step S58, the detection deviation is -1.
The minimum value of -15 dB in the range of 7 dB to step S48
0.1 dB is set every 200 mS for 2 dB. Therefore, in step S58, (2 dB /
During a recovery time of 4 seconds (at 0.1 dB × 200 mS = 4 S), an attenuation amount of 2 dB is output to the electronic volume 1, and at the same time, the detection deviation of −17 dB is also reduced by 2 dB to be −15 dB.

When the process proceeds from step S58 to step S47, since the detection deviation is -15 dB, it falls within the range of step S47 and the process proceeds to step S57. In step S57, the detection deviation is changed from -15 dB to step S4.
Within 5 dB, which is the minimum value of -10 dB in the range of 7,
Set 0.1 dB every 50 mS. Therefore, in step S57, (5 dB / 0.1 dB × 150 mS =
During a recovery time of 7.5 seconds (at 7.5S), an attenuation amount of 5 dB 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.

When the process returns from step S57 to step S46, since the detection deviation is -10 dB, it falls within the range of step S46 and the process proceeds to step S56. In step S56, the detection deviation is changed from -10 dB to step S46.
Of the minimum value of -5 dB in the range of
Set 0.1 dB for each mS. Therefore, in step S56, (5 dB / 0.1 dB × 100 mS = 5S
During the recovery time of 5 seconds, the attenuation of 5 dB is output to the electronic volume 1 and at the same time, the detection deviation is -10 dB.
Is also reduced by 5 dB to −5 dB.

The same operation is repeated thereafter, and the operation is finally ended in step S51. As a result, the recovery time is 0.9 seconds in step S55 and step S54.
1.0 seconds, step S53 1.2 seconds, step S5
2 is set for 1.5 seconds, and step S51 is set for 2.0 seconds. Overall recovery time is 4 + 7.5 + 5 + 0.9
+ 1.0 + 1.2 + 1.5 + 2.0 = 23.1 seconds, during which the attenuation amount of the electronic volume 1 changes as shown in FIG. 9 and returns to the original attenuation amount.

FIG. 9 shows a case where the detection deviation 19 is -17 dB and a case where it is -2 dB, -7 dB, and -12 dB. When the value of the detection deviation 19 is any other value, the same operation as described above is performed, and the attenuation amount changes with the progress shown in FIG. As shown in this graph, when the amount of attenuation is large, the recovery time is set longer than when the amount of attenuation is small, and when the audio signal is reproduced, it can be received with a natural feeling.

The attack time and the recovery time can be easily changed by changing the numerical values shown in the flowcharts of FIGS. 6 to 8 in the attenuation rate setting means 20.

[0045]

According to the present invention, in the automatic audio signal amplitude control device, the attenuation amount of the variable attenuator can be automatically changed according to the level of the input analog audio signal, and the input is made. Even if the level of the audio signal fluctuates significantly, it can be kept within a predetermined range.

According to the present invention, the attack time and the recovery time of the variable attenuator can be changed according to the level of the input signal of the A / D converter, and the response time of the attack time and the recovery time of the variable attenuator can be changed. The characteristics can be controlled freely.

[Brief description of drawings]

FIG. 1 is a block diagram (part 1) of an embodiment of an automatic audio signal amplitude control apparatus of the present invention.

FIG. 2 is a block diagram (No. 2) of an embodiment of the audio signal automatic amplitude control device of the invention.

FIG. 3 is a flowchart illustrating the operation of the attenuator 8 of FIG.

FIG. 4 is a flowchart (No. 1) explaining the overall operation of the control device of FIG.

5 is a flowchart (part 2) explaining the overall operation of the control device in FIG. 1. FIG.

FIG. 6 is a flowchart for explaining the operation when increasing the attenuation amount of the electronic volume in FIGS. 1 and 2.

FIG. 7 is a flowchart (No. 1) for explaining the operation when restoring the increased attenuation amount of the electronic volume in FIGS. 1 and 2;

FIG. 8 is a flowchart (No. 2) for explaining the operation when restoring the increased attenuation amount of the electronic volume in FIGS. 1 and 2;

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

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

FIG. 11 is a block diagram of a conventional audio signal automatic amplitude control device using a variable attenuator using a transistor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electronic volume 2 ... Low-pass filter 3 ... A / D converter 4 ... Digital signal processor 5 ... D / A converter 6 ... Input terminal 7 ... Output terminal 8 ... Attenuator 11 ... Microcomputer 12 ... A / D converter 13 ... reading means 14 ... comparing means 15 ... reference value 16 ... ATT value setting means 17 ... comparing means 18 ... reference value 19 ... detection deviation 20 ... attenuation rate setting means

Claims (2)

[Claims] 1. An A / which converts a voice signal into a digital value.
D converter, electronically controlled variable attenuator provided in front of the A / D converter, reading means for reading the output voltage of the electronically controlled variable attenuator at regular intervals, and the read output voltage level as a reference level. Comparing means for comparing and outputting a detection deviation, and attenuation rate setting means for changing the attenuation rate of the electronically controlled variable attenuator by setting an attack time and a recovery time according to the detection deviation when the detection deviation is detected. An automatic audio signal amplitude control device comprising: 2. An A / D converter is provided in front of the reading means, and an attenuator for attenuating the input level of the A / D converter to a level below a permissible value when the input level exceeds the maximum permissible value is provided. The automatic audio signal amplitude control device according to claim 1, wherein the automatic amplitude control device is provided before the A / D converter.