JPH088461B2 - Digital automatic gain controller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital automatic gain control device used for voice signal processing such as voice synthesis (mixing) and voice level adjustment in a telephone line.

[Conventional technology]

In recent years, the development of the communication field has been remarkable, and many new products have been produced. For example, by connecting multiple terminals, a video conference system that allows people who are far from each other to hold a conference without moving,
A voice mail device or the like that can leave a voice message even when the receiving person is absent is a prominent example, and this saves time as much as possible. These new inventions play a large role in a busy urban society, and they are greatly impressed from all perspectives. Recently, realization of more natural voice and cheaper usage charge is desired, and new innovation in the transmission field is expected.

An automatic gain control device is one of those that meet the realization of high quality voice. Automatic Gain Con
torol (hereinafter referred to as AGC) is a function to keep the output within a certain range even when the input signal level range is wide.To compensate for the loss due to transmission and to adjust the signal level of transmission and reception, It is also used for signal processing and has made a great contribution to the development of the communication field.

This AGC operation is usually performed by an analog circuit using an operational amplifier. However, due to the recent development of digital processing technology, it has become possible to perform this AGC operation by a digital circuit. Further, at present, many digital signal processing processor systems implement a digital AGC circuit, and an AGC device for a more limited purpose is being developed.

FIG. 3 is an example of a system diagram showing an outline of a digital AGC device. The analog signal A _in which AGC should be applied is
Converted to digital signal X by A / D converter (1),
The digital signal X is input into the AGC loop AL of the digital AGC system. Now enter the multiplier (2),
The AGC coefficient y is multiplied by the multiplication with the AGC coefficient Ag, that is, y
= Ag · X. The output y is branched and enters the AGC coefficient generator (5) through the level detection circuit (3) and the averaging circuit (4). Here, the AGC coefficient Ag is determined for each output y by going through the AGC loop AL once.

As an example of hardware implementation of the AGC loop AL in FIG. 3, as shown in FIG. 4, for example,
There is one disclosed in Japanese Examined Patent Publication No. 63-19089. Less than,
The operation of FIG. 4 will be described in detail.

The input audio signal A _in is converted into a digital signal X by the A / D converter (1) and then given to this circuit. The digital input signal X is first input to the multiplier (2), where
The AGC coefficient Ag is multiplied to calculate the AGC output signal y. The digital output signal y is branched into the AGC loop and first input to the adder (32) through the squaring circuit (31) to detect the level. However, it is input to the adder (32) as a negative input. A reference value Dr is separately applied to the adder (32), which is given to the multiplier (41) as a negative input when the output y exceeds Dr and as a positive input when y falls below Dr. Then, constant weighting (weighting coefficient a) is performed. The adder (42) including the multiplier (41) and the delay circuit T ₁ perform averaging. Note that b for the multiplier (51) and 1.0 for the adder (52) both relate to weighting, and here the AGC coefficient Ag is determined and generated.

Further, the delay circuit T ₁ becomes the delay circuit T outputs Y ₁ to comprising a multiplier and a memory for the weighting of a number less than 1 e of the adder (42), the output Y ₁ is And is averaged.

[Problems to be Solved by the Invention]

Since the conventional digital AGC device is constructed as described above, it has the following problems. That is, in FIG. 4, the loop including the adder (42) and the delay circuit T ₁ constitutes an integrator to calculate an average value, and the integrator adds all the input values. But
Since the telephone line is not always in a call state, data is taken in even in a silent state where no voice signal is detected. Therefore, if these values are averaged uniformly, the average value depends on the situation at the time of extraction, and there is a risk of calculating an inappropriate value in order to keep the level of the audio signal constant.

Further, from such a technical point of view, JP-A-60-22815
The publication discloses a technique of controlling the gain of the AGC circuit while the signal is being received, writing the same to the memory, and reading from the memory when the signal is cut off. The optical signal is based on the assumption that the level of the received signal does not change during the duration of the signal in the short time, and the amplitude of the signal always changes significantly during the duration of the signal. Depending on the voice signal in which the signal and the silent signal appear, there is a signal disconnection accordingly, and when applied to the voice signal, the calculation of the gain value is interrupted every time the signal disconnects every short time, which is peculiar to the voice signal. However, since the signal level of the new voiced section is not always the same as the level of the previous voiced section, a step-like change occurs in the control output calculated based on this and a stable profit is obtained. It can not be controlled.

The present invention has been made to solve the above problems, and provides a digital AGC device capable of generating a stable gain so that target audio data as an input signal undergoes a more natural level adjustment. The purpose is to get.

[Means for solving the problem]

A digital AGC device according to the present invention comprises a multiplier for multiplying a digital signal obtained by digitally converting an analog input signal of an acoustic signal by an A / D converter, and a level for detecting an output level of the multiplier. An automatic gain control loop including a detection circuit, an averaging circuit that extracts an average value based on the detection level, and a gain coefficient generation unit that calculates a gain coefficient based on the average value and outputs the gain coefficient to the multiplier. In the provided digital automatic gain control device, the target is an acoustic signal whose amplitude constantly changes significantly, and in which a sound and a silence appear in a short time.
A voice detector for determining whether the digital signal is voiced or not, and an average value is obtained in a time period longer than at least one wavelength, and when the digital signal is not voiced, the multiplier is provided to the multiplier based on the output of the voice detector. And a control means for setting the output gain coefficient as the previous sample value.

[Action]

In the digital AGC device according to the present invention, a voice detector for detecting voice is added to the AGC loop, and it is determined whether the voice as an input signal is voiced or silent. Then, the control unit ignores the silent input signal, inputs the average output signal in the presence of sound instead of the input signal, takes an average, and sets the target for calculating the coefficient for averaging the silent noise. To prevent this, the gain given to the previous sample is retained during the silent period. During averaging, the voice detector added to the AGC loop examines the characteristics of the input signal and extracts only the voice, so noise in a silent state can be ignored, and a stable gain commensurate with the input is given to the output signal.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1 in which the same parts as those in FIGS. 3 and 4 are designated by the same reference numerals.
FIG. 1 is a block diagram showing an embodiment of the present invention,
(2), (31), (32), (41), (42), (51),
(52) and T ₁ are the same as those of the conventional device shown in FIG. In this embodiment, between an adder (42) and a delay circuit T _{1 which} are parts for averaging in the AGC loop, a selector device (64) and a switch (64) for switching the circuit between a voiced state and a silenced state. 65) and a noise threshold value C is set separately, and a comparator (63) for comparing the threshold value C with the voice which is the input signal is provided to provide the comparator (6).
By 3), the circuit is switched when there is sound and when there is no sound. The delay circuit T ₁ and the selector device (6
A multiplier (67) for weighting 1 / a is provided between the multiplier and (4).

Next, the operation will be described in detail. The digital AGC device according to the present invention, similar to the conventional digital AGC system, converts the analog voice input signal A _in into the digital signal X by the A / D converter (1), and then, in the AGC loop. In parallel with the processing, the following digital arithmetic processing is performed.

That is, a digital output signal X with its level extracted by the square circuit (61), averaged by the adder (62) and the delay circuit T _2, then the weighting of b 'is performed in the multiplier (66). At this time, the time constant of the delay circuit T ₂ is sufficiently smaller than that of the delay circuit T ₁ in the AGC loop, but it is sufficient to detect the instantaneous level of the audio signal. After that, it compares with the noise threshold C which is set separately by the comparator (63),
It is determined whether the data is voiced or silent. The result is sent to the selector device (64) provided between the adder (42) and the delay circuit T ₁ . The selector device (64) forms a loop by connecting the switch (65) to the ON side when the input signal X is sound based on the output of the comparator (63) to perform averaging. When X is determined to be silent, the switch (65) is connected to the OFF side. The gain generated at this time is the same as that applied to the previous sample.

FIG. 2 shows the signal and the gain value at each place when the automatic gain control method is applied to the input signal. B) is the input signal, b) is the input signal a) squared by the squaring circuit (61), and then integrated by the adder (62) and the delay circuit T ₂ . The gain generated from the AGC device, as well as d) is the AGC to which the present invention is applied.
It shows the gain in the case of the device. As can be seen from this figure, the gain generated from the AGC device to which the present invention is applied has little fluctuation.

Therefore, even if there is a turning point or silence during a call, the circuit that performs averaging excludes it from the averaging target and performs processing, so that even input data that has large level fluctuations is stable. There is an effect that the average value obtained can be obtained.

In the above embodiment, the double circuit (61) is used to extract the level, but the same effect can be obtained by taking the absolute value instead.

Further, the automatic gain device of the present invention can be performed by software processing centered on a processor.

〔The invention's effect〕

As described above, according to the present invention, by detecting the voice in the AGC loop, it becomes possible to process the input signal at the time of silence, and output level more than necessary at the time of sound rising after the silence period elapses. There is an effect that a stable gain can be given to the audio signal level without raising the value, and a more natural audio signal level adjustment can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 illustrates gain values generated for input signals in a conventional digital AGC system and a digital AGC system to which the present invention is applied. FIG. 3 is a characteristic diagram, FIG. 3 is a system diagram showing an outline of a conventional digital AGC system, and FIG. 4 is a block diagram showing FIG. 3 as hardware. (31) and (32) are the square circuit and adder (41), (42), and T ₁ that make up the level detection circuit are the multiplier, adder, and delay circuit (51) that are the averaging level detection circuit. (52) is a multiplier, adder and delay circuit that compose the automatic gain control coefficient generator (61), (62), (63), (66), T ₂ is a square circuit that composes the voice detector, and addition A selector, a comparator, a multiplier and a delay circuit (64) and (65) constitute a control means, and a selector device and a switch AL are automatic gain control loops. In each drawing, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A multiplier for multiplying a digital signal obtained by converting an analog input signal of an acoustic signal by an A / D converter by a predetermined gain coefficient, a level detecting circuit for detecting an output level of the multiplier, and A digital automatic system having an automatic gain control loop consisting of an averaging circuit for extracting an average value based on the detection level and a gain count generating section for calculating a gain coefficient based on the average value and outputting the gain coefficient to the multiplier. In the gain control device, a voice detector for determining whether the digital signal is voiced or not, and an average value is obtained in a time period longer than at least one wavelength, and when the digital signal is not voiced, based on the output of the voice detector. And a control means for setting the gain coefficient to be output to the multiplier as a pre-sampled value.