JP2002016461A - Signal level controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease waveform distortion in the case of controlling a signal, which exceeds a saturation level, into proper signal level, to suppress the increase of a white noise at the time of silence, and to simplify circuit scale and arithmetic processing concerning a signal level controller for controlling the signal level of audio or the like. SOLUTION: The gain of a gain storage part 1-9 is multiplied to an input signal in by a gain multiplying part 1-1 and outputted as an output signal out. When it is detected by a gain monitoring part 1-2, the gain exceeds a prescribed threshold and when it is detected by an output level saturation monitoring part 1-3, an output signal level exceeds a prescribed saturation level, a coefficient >1 selected by a coefficient selecting part 1-7 is multiplied to the gain, and the gain is gradually decreased. Besides, in the other case, a coefficient exceeding '1' is multiplied to the gain and the gain is gradually increased. Since the gain is smoothly transited and does not exceed the prescribed threshold, the waveform distortion is decreased and the increase of the white noise at the time of silence is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal level adjusting device for adjusting a signal level of an audio signal or the like, and relates to a voice-compatible device for distributing an audio signal (Voice) over an IP network which is spreading with the spread of the Internet. The present invention relates to a signal level adjusting device for adjusting a signal level of a signal in a voice band transmitted and received by a private branch exchange (PBX), an ISDN communication device, or a communication device such as a mobile terminal such as a mobile phone or a PHS.

In a communication device such as the one described above, when a conference call service for generating a synthesized sound by adding a plurality of audio signal levels is performed, it is possible to prevent waveform distortion from occurring when the signal level exceeds the saturation level of the amplifier. If the signal level is attenuated to prevent the signal level, or if the signal is transmitted through a plurality of repeaters, the signal level is adjusted to correct the signal level from being lowered or becoming unstable. It is necessary. The present invention relates to a signal level adjusting device that has a small waveform distortion and does not increase white noise during silence.

[0003]

2. Description of the Related Art Conventionally, an automatic gain controller (AGC; AGC) has been used to prevent signal level saturation due to addition of voice signal levels in a conference call service and signal level instability due to deterioration of transmission quality when passing through a plurality of repeaters. Auto g
ain Control) to adjust the signal level. FIG. 4 shows the configuration of the automatic gain controller (AGC).

As shown in FIG. 4, a conventional automatic gain controller (AGC) includes a gain multiplying unit 4-1 for multiplying an input signal level and a gain, and a memory 4-2 for extracting and storing a plurality of output signal levels. An average calculator 4-3 for calculating an average of a plurality of output signal levels, a reciprocal calculator 4-4 for calculating a reciprocal of the average, a memory 4-2, an average calculator 4-3, and a reciprocal calculator 4-4. 4 and a control unit 4-5 for controlling

[0005] The auto gain controller (AGC)
The input signal (in) is multiplied by the gain in the gain multiplier 4-1 and output, and the level value of the output signal (out) is sequentially stored in a plurality of in the memory 4-5. By the time the next input signal (in) is input, the memory 4-5
The average value is calculated by the average calculation unit 4-4 based on the plurality of output signal levels stored in the storage unit, and the reciprocal of the average value is calculated by the reciprocal calculation unit 4-3. Input to the unit 4-1 and the gain product unit 4-1 multiplies the next input signal by the reciprocal.

As described above, the auto gain controller (AGC) calculates a gain by performing feedback based on a plurality of output signal levels so that the output signal level is kept substantially constant with respect to the input signal. , The gain is multiplied by the input signal to adjust the signal level.

FIG. 5 shows a flow of calculating an average value and a reciprocal in a conventional auto gain controller (AGC). Here, in is the input signal level, out is the output signal level, typ is the gain calculation register, a is the number of output signals whose average value is to be calculated, n is the number of times the output signal level is added, and memory (m) is the output. This shows a memory at an address m for storing a signal level.

First, in order to calculate the average value of the output signal levels, a process of storing the sum of the output signal levels stored in the memory (0) to the memory (a-1) in the gain calculation register typ is performed. The processing is performed by using “t” with n as a parameter.
yp = memory (n + 1) + type "(step 5
-1) and step 5-1 until "n = a-1"
Is repeated (step 5-2).

Next, according to "type = type / a", the average value is calculated by dividing the total value of the output signal levels by the number a, and the average value is stored in the gain calculation register typ (step 5).
-3). Next, the reciprocal of the average value is calculated by “type = 1 / type”, and the reciprocal is used as a gain to obtain a gain calculation register t.
yp (step 5-4).

Next, when an input signal is input, "out =
in · type ”, the input signal level in has a gain ty
The product is multiplied by p and the product value is output as an output signal (step 5-5). Then, the output signal level out is stored in the memory (m) (step 5-6).

In order to process the next input signal, "m = Mod (m + 1, a)", "n = -1",
Based on “type = 0”, the storage address of the next output signal level out is calculated, and the output signal level addition count n
Of the gain calculation register t
yp is set to an initial value "0" (step 5).
-7), returning to step 5-1 to repeat the same processing.

Note that "m = Mod (m + 1, a)" is
(M + 1) represents the remainder when divided by a, and the memory address for storing the output signal level out is sequentially incremented each time an output signal is output, and the output signal is stored in the memory (a-1) of the last storage unit. After storing the level out,
Returning to the memory (0) of the head storage unit again, the memory storage address is calculated so that the output signal level out is stored. Therefore, the oldest output signal level out is replaced with the latest output signal level out and stored.
Output signal level o by IFO (first in first out)
ut is stored.

FIG. 6 shows input / output characteristics of a conventional auto gain controller (AGC). FIG. 6A shows an input waveform exceeding a saturation level and an output waveform when the auto gain controller (AGC) is not used. Shows a state of being distorted by being clamped.

FIG. 2B shows the output magnification of the auto gain controller (AGC). If the input level is a small value such as when there is no sound, the output magnification (amplification rate) of the auto gain controller (AGC) becomes This is an extremely large value, and a very small noise level is greatly amplified, causing unpleasant white noise.

FIG. 3C shows the state of fluctuation of the input / output waveform of the automatic gain controller (AGC). When there is no sound or no signal, the automatic gain controller (AGC)
The output magnification (amplification rate) of is a very large value,
If a signal such as a voice is suddenly input in such a state, the output magnification (amplification factor) of the auto gain controller (AGC) suddenly undergoes attenuated transition, and as a result, the head portion of the output waveform is distorted. .

[0016]

When the above-mentioned auto gain controller (AGC) is used for adjusting the signal level,
When there is no sound or no signal, minute white noise is greatly amplified,
In addition, when a signal is input in a silent or no-signal state, the amplification factor changes rapidly, so that there is a problem that the leading portion of the output waveform of the input signal is distorted.

An automatic gain controller (AG)
In C), since the average value and the like must be calculated based on a plurality of output signal levels, the load of the arithmetic processing is heavy, and a memory for storing a plurality of output signal levels must be provided. There was a problem that the circuit scale became large.

In order to reduce the distortion of the head portion at the start of signal input, the time width of the signal to be averaged is expanded so that the entire time width of the average is calculated to be silent or no signal. It is also possible to reduce the probability of abrupt changes in amplification factor from silence or no-signal state, but in order to do so, it is necessary to increase the amount of storage memory for output signal levels, and Since it is necessary to calculate an average value for a large number of output signal levels before the next signal is input, high-speed arithmetic processing capability is required,
It is expensive and has a large circuit scale.

According to the present invention, a high-level input signal is attenuated to a saturation level or less, there is no increase in white noise in a no-signal input state such as when there is no sound, and the waveform distortion at the beginning at the start of signal input is small. It is an object of the present invention to provide a signal level adjustment device that adjusts a signal level with a simple arithmetic function and a small circuit scale.

[0020]

According to the present invention, there is provided a signal level adjusting apparatus comprising: (1) a gain multiplying unit for outputting a product of an input signal level and a gain as an output signal; and determining whether the gain exceeds a predetermined threshold. A gain monitoring unit that monitors whether the output signal level has exceeded a predetermined saturation level, and an output level saturation monitoring unit that monitors whether the output signal level has exceeded a predetermined saturation level. The gain monitoring unit detects that the gain has exceeded a predetermined threshold. Each time, and every time the output level saturation monitoring unit detects that the output signal level exceeds a predetermined saturation level, the gain is gradually reduced by multiplying the gain by an adjustment coefficient of less than 1, and the gain monitoring unit and Each time the output level saturation monitor detects that the gain is below a predetermined threshold and the output signal level is below a predetermined saturation level, the gain is gradually increased by multiplying the gain by an adjustment coefficient exceeding 1. Those having a gain control means.

(2) The gain control means includes a gain storage unit for storing gain, an adjustment coefficient storage unit for storing adjustment coefficients less than 1 and more than 1, and a gain output from the gain storage unit. Multiplying an adjustment coefficient less than 1 or more than 1 and inputting the product value to a gain storage unit;
An adjustment coefficient selection unit that selects one of the adjustment coefficients less than 1 or more than 1 stored in the adjustment coefficient storage unit and outputs the selected adjustment coefficient to the gain adjustment coefficient multiplying unit; It is configured to select one of the adjustment coefficients less than 1 or more than 1 stored in the adjustment coefficient storage section based on the outputs of the monitoring section and the output level saturation monitoring section.

(3) The adjustment coefficient multiplied by less than 1 or greater than 1 is a numerical value close to 1 so that the gain fluctuates more slowly than the level fluctuation with respect to the level fluctuation of the input signal. It was done.

With such a configuration, the gain is kept below a predetermined threshold value when no sound or no signal is input, an increase in white noise when no sound or no signal is input is suppressed, and the gain with respect to a change in the input signal is suppressed. , The distortion of the output signal due to sudden input fluctuation is suppressed. Also, since the gain is adjusted so that the output signal level does not exceed the saturation level, even if multiple audio signals are added such as in a conference telephone service, the signal is attenuated to an appropriate level and waveform distortion due to saturation is prevented. Can be.

[0024]

FIG. 1 shows the configuration of a signal level adjusting device according to the present invention. In FIG. 1, reference numeral 1-1 denotes a gain product unit for outputting a product of an input signal and a gain as an output signal;
2 is a gain monitor for monitoring whether the gain exceeds a predetermined threshold, 1-3 is an output level saturation monitor for monitoring whether the output signal level exceeds a predetermined saturation level, 1-.
4 is a logical sum (OR) output unit, 1-5 is an adjustment coefficient storage unit for storing an adjustment coefficient less than 1, 1-6 is an adjustment coefficient storage unit for storing an adjustment coefficient exceeding 1, and 1-7 is an adjustment coefficient storage unit less than 1. Or, an adjustment coefficient selection unit that selects and outputs one of one or more adjustment coefficients, 1-8 is a gain adjustment coefficient multiplication unit that multiplies the gain by an adjustment coefficient less than 1 or more than 1, and 1-9 stores the gain. The gain storage register 1-10 is a linear amplifier.

The input signal in is supplied to a gain storage register 1-9.
Is multiplied by the gain product unit 1-1 and output as an output signal out. Note that, as shown in FIG. 1, one of the two gain multiplication units 1-1 is provided instead of the configuration in which two gain multiplication units 1-1 are provided and the input signal in is multiplied twice by the gain. May be omitted.
Further, a linear amplifier 1-10 having a predetermined amplification factor may be arbitrarily arranged on the output side of the gain product section 1-1.

The gain stored in the gain storage register 1-9 is monitored by a gain monitor 1-2 to determine whether it exceeds a predetermined threshold. If the gain exceeds the predetermined threshold, the gain monitor 1
-2 outputs a logic signal "1". In addition, the gain multiplication unit 1
The output signal from -1 is monitored by the output level saturation monitoring section 1-3 as to whether it exceeds the saturation level. When the output level exceeds the saturation level, the output level saturation monitoring section 1-3 outputs a logical signal "1".

The logical sum (OR) output section 1-4 receives the logical signals output from the gain monitoring section 1-2 and the output level saturation monitoring section 1-3, and outputs the logical sum signal to the adjustment coefficient selecting section 1. The signal is output to -7 as a signal for selection control.

The adjustment coefficient selection unit 1-7 performs a logical sum (OR)
When the logic signal “1” is input from the output unit 1-4, that is, when the gain exceeds a predetermined threshold value or the level of the output signal reaches the saturation level, it is set in the adjustment coefficient storage unit 1-5. An adjustment coefficient less than 1 is selected and output.

On the other hand, the adjustment coefficient selection section 1-7 receives the logical signal "0" from the logical sum (OR) output section 1-4, that is, the gain is equal to or less than a predetermined threshold value and the level of the output signal is Is less than or equal to the saturation level, an adjustment coefficient exceeding 1 set in the adjustment coefficient storage unit 1-6 is selected and output.

The adjustment coefficient storages 1-5 and 1-6 respectively store a numerical value slightly smaller than 1 (for example, 0.9999) as an adjustment coefficient less than 1 and a numerical value slightly larger than 1 as an adjustment coefficient exceeding 1. (For example, 1.00001)
Is set.

The gain adjustment coefficient multiplying section 1-8 multiplies the adjustment coefficient output from the adjustment coefficient selection section 1-7 by less than 1 or more than 1 by the gain output from the gain storage register 1-9. The result of the multiplication is input to a gain storage register 1-9.
The multiplication result input from -8 is stored as a new gain.

FIG. 2 shows an operation flow of the signal level adjusting device of the present invention. The gain stored in the gain storage register is
The magnitude is compared with a predetermined threshold (2-1). If the gain is larger than the predetermined threshold, that is, if a borrow occurs when the gain is subtracted from the predetermined threshold, the gain is less than 1. Multiply by an adjustment coefficient (eg, 0.9999) (2-
2) The gain multiplied by the adjustment coefficient less than 1 is input signal i
n and outputs an output signal out (2-3).

The output signal level out and the saturation level are compared in magnitude (2-4), and when the output signal level out is larger than the saturation level, that is, when the output signal level out is subtracted from the saturation level, a borrow ( If a borrow occurs, the gain has an adjustment factor less than 1 (eg, 0.999).
9) (2-2), and multiplies the input signal in by the gain multiplied by the adjustment coefficient less than 1 to output the output signal out (2-3).

When the gain is smaller than a predetermined threshold value and when the output signal level is equal to or lower than the saturation level, the gain is multiplied by an adjustment coefficient exceeding 1 (for example, 1.00001) (2−2).
5), multiply the input signal in by the gain multiplied by the adjustment coefficient exceeding 1, and output the output signal out (2-6).

FIG. 3 shows the input / output waveform and output magnification of the signal level adjusting device of the present invention. FIG. 3A shows an input waveform exceeding the saturation level and its output waveform. According to the present invention, when a high-level signal waveform whose output waveform exceeds the saturation level is input, the gain gradually increases. Since the output waveform is attenuated, the output waveform gradually becomes a waveform without distortion, and the occurrence of waveform distortion is suppressed.

FIG. 7B shows the output magnification of the level adjusting device according to the present invention. According to the present invention, the gain is always equal to or less than a predetermined threshold (for example, 1). As described above, the output magnification (amplification rate) is also equal to or less than a predetermined value (for example, 1), and when the input signal is a small value such as when there is no sound as in the case of using an automatic gain controller (AGC), the output magnification (amplification rate) is It is not limited and does not become a large value, and generation of harsh white noise can be limited.

FIG. 3C shows a case where a signal such as a voice is input after a silence state. In the present invention, when an input signal is suddenly input after a silence state, the output signal level is reduced. The gain does not fluctuate as long as it does not exceed the saturation level, and even when the output signal level exceeds the saturation level, the gain (amplification factor) gradually attenuates gradually, so that the distortion at the head of the output signal is extremely small. It will be.

The signal level adjusting apparatus of the present invention can be used to perform a conference call when making a voice call on the Internet using a voice-compatible device or a voice call via an analog line, an ISDN line, or a wireless line such as a mobile phone or PHS. This reduces the waveform distortion due to an increase in the signal level exceeding the saturation level, which occurs when the audio signal is added, and suppresses the increase in white noise during silence.

In addition, for communication performed via a modem (MODEM) for converting a data signal into a voice band signal, the signal level adjusting device of the present invention is applied to a modem (MODEM) or the like, thereby achieving waveform distortion. And white noise are reduced, and bit errors and communication failures can be reduced.

[0040]

As described above, according to the present invention,
When the signal level exceeds the saturation level and when the gain exceeds a predetermined threshold, the gain is gradually reduced, and when the signal level is below the saturation level and the gain is below the predetermined threshold, the gain is gradually increased. By doing so, it is possible to adjust the signal level to an appropriate level by suppressing the occurrence of waveform distortion at the beginning of a signal that exceeds the saturation level, such as when adding sound, and when there is no sound or no signal input. Since the gain is maintained at or below the predetermined threshold even during the period, it is possible to limit an increase in white noise when there is no sound or when there is no signal input.

Further, according to the present invention, since only the operation of comparing the output signal level and the gain with a predetermined value and the operation of multiplying the gain by a predetermined coefficient are performed, the operation function is simplified as compared with the auto gain controller. Since high-speed processing is not required and a memory for storing a plurality of output signal levels for calculating an average value is not required, the circuit scale can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a signal level adjusting device of the present invention.

FIG. 2 is a diagram showing an operation flow of the signal level adjusting device of the present invention.

FIG. 3 is a diagram showing an input / output waveform and an output magnification of the signal level adjusting device of the present invention.

FIG. 4 is a diagram showing a configuration of a conventional auto gain controller (AGC).

FIG. 5 is a flowchart for calculating an average value and a reciprocal in a conventional auto gain controller (AGC).

FIG. 6 is a diagram showing input / output characteristics of a conventional auto gain controller (AGC).

[Explanation of symbols]

 1-1 Gain product section 1-2 Gain monitoring section 1-3 Output level saturation monitoring section 1-4 OR (OR) output section 1-5 Adjustment coefficient storage section for storing an adjustment coefficient less than 1 1-6 1 Adjustment coefficient storage unit that stores adjustment coefficients exceeding 1-7 Adjustment coefficient selection unit 1-8 Gain adjustment coefficient multiplication unit 1-9 Gain storage register 1-10 Linear amplifier

Claims (3)

[Claims] A gain multiplying unit that outputs a product of an input signal level and a gain as an output signal; a gain monitoring unit that monitors whether the gain exceeds a predetermined threshold; An output level saturation monitoring unit that monitors whether or not a saturation level has been exceeded.Each time the gain monitoring unit detects that a gain has exceeded a predetermined threshold, and an output signal level is adjusted by the output level saturation monitoring unit. Each time it is detected that the predetermined saturation level has been exceeded, the gain is gradually reduced by multiplying the gain by an adjustment factor of less than 1, and the gain monitoring unit and the output level saturation monitoring unit determine that the gain is equal to or less than a predetermined threshold and Each time the output signal level is detected to be below the predetermined saturation level, the gain is set to 1
A signal level adjusting device comprising: gain control means for multiplying the gain by an adjustment coefficient exceeding. 2. The gain control means includes: a gain storage unit for storing gain, an adjustment coefficient storage unit for storing adjustment coefficients less than 1 and more than 1, and a gain output from the gain storage unit.
A gain adjustment coefficient multiplication unit that multiplies an adjustment coefficient less than 1 or more than 1 and inputs the product value to a gain storage unit; and an adjustment coefficient less than 1 or more than 1 stored in the adjustment coefficient storage unit An adjustment coefficient selection unit that selects one of them and outputs the adjustment coefficient to the gain adjustment coefficient multiplication unit, wherein the adjustment coefficient selection unit stores an adjustment coefficient based on the outputs of the gain monitoring unit and the output level saturation monitoring unit. The signal level adjusting device according to claim 1, further comprising a configuration for selecting one of an adjustment coefficient less than 1 and an adjustment coefficient exceeding 1 stored in the unit. 3. An adjustment coefficient multiplied by less than 1 or greater than 1 by a value close to 1 so that the gain fluctuates more slowly than the level fluctuation with respect to the level fluctuation of the input signal. The signal level adjusting device according to claim 1 or 2, wherein