JPH037411A - Digital automatic gain controller - Google Patents

Abstract

PURPOSE:To generate a stable gain so as to allow a voice data to receive more natural level adjustment by using a gain coefficient outputted to a multiplier based on an output of a voice detector as a sample when a digital signal represents no sound state. CONSTITUTION:A level of a digital output signal X is extracted by a square circuit 61, an adder 62 and a delay circuit T2 average the level and a multiplier 66 gives a weight of b' to the averaged level. Then the result is compared with a noise threshold level C set separately at a comparator 63 to decide whether the data represents a voiced sound or no sound. The result is sent to a selector 64 provided between an adder 42 and a delay circuit T1. The selector 64 allows a switch 65 to be thrown to the position of ON when an input signal X represents a voiced sound based on the output of the comparator 63 thereby forming a loop for averaging. Moreover, the selector 65 allows the switch 65 to be thrown to the position of OFF when the input signal X is decided to be no sound. Then natural voice signal level adjustment is attained.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to speech synthesis (mixing) on a telephone line.
This invention relates to a digital automatic gain control device used in audio signal processing such as sound level adjustment and audio signal processing.

(Conventional technology) In recent years, the field of communications has made remarkable progress, and many new products have been created.For example, by connecting multiple terminals, people who are located far away from each other can avoid working eight shifts. A TV conference system that allows you to hold meetings,
A prominent example is a voice mail system that allows voice messages to be left even when the person on the receiving end is not available, thereby saving as much time as possible.

The role these new inventions play in our busy urban societies is significant, and they are of great interest from all perspectives.

Recently, there has been a desire to realize more natural sound and lower usage fees, and new innovations in the transmission field are expected.

An automatic gain control device is one of the devices that help achieve this high quality audio. Automatic gain control (Auto-matlc)
Ga1n Control (hereinafter referred to as AGC) is a function that maintains the output within a certain range even when the range of input signal levels is wide.It is used to compensate for losses associated with transmission and adjust the magnitude of the signal level for transmission and reception. It is also used in audio signal processing, making a major contribution to the development of the communications field.

This AGC function has normally been performed by an analog circuit using an operational amplifier. However, with the recent development of digital processing technology, it has become possible to perform this AGC function using a digital circuit. Furthermore, many digital signal processing processor systems are now implementing digital AGC circuits, and AGC devices for more limited purposes are being developed.

FIG. 3 is an example of a system diagram showing an overview of a digital AGC device. Analog signal Al to be applied AGC
n is converted by an A/D converter (1) into a gain digital signal X, and the digital signal X is input into the AGC loop AL of the digital AGC system. Here, it enters the multiplier (2) and is multiplied by the AGC coefficient Ag, resulting in an AGC output y, that is, y=Ag-x. Output y is branched to level detection circuit (3) and averaging circuit (4)
It then enters the AGC coefficient generation section (5). Here, the AGC coefficient Ag is determined for each output y by going around the AGC loop AL.

As an example of hardware implementation of the AGC loop AL shown in FIG. 3, there is one shown in Japanese Patent Publication No. 19089/1989, as shown in FIG. 4, for example. The operation shown in FIG. 4 will be explained in detail below.

The human voice signal Aln is converted into a digital signal X by an A/D converter (1) and then applied to this circuit. The digital input signal X is first input to the multiplier (2), where it is multiplied by the AGC coefficient Ag to calculate the AGC output signal y. The digital output signal y is branched into the AGC loop and first inputted to an adder (32) via a squaring circuit (31) to detect the level. However, the adder (32) receives the human power as minus human power. A separate reference value D' is applied to the addition II (32), and when the output y exceeds D', it is used as a negative input, and conversely, when y is less than D', it is used as a positive input and applied to the multiplier (41). )
is given a certain weight (weighting coefficient a). The adder (42) and delay circuit T, including this multiplier (41), perform averaging. In addition, the multiplier (51)
b for , and 1 and 0 for the adder (52) are both related to weighting, and the AGC coefficient Ag is determined and generated here.

Further, the delay circuit TI is a delay circuit T consisting of a multiplier and memory that weights the output Yl of the adder (42) by a number a smaller than 1, and the output Yl is ] 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 T1 constitutes an integrator to calculate the average value, and the integrator adds all input values. However, since the telephone line is not always in a talking state, data is captured even in a silent state where no voice signal is detected. Therefore, if these are averaged regularly, the average value will depend on the situation at the time of extraction, and there is a risk of calculating a value that is inappropriate for trying to keep the level of the audio signal constant.

Also, from such a technical standpoint, Japanese Patent Application Laid-Open No. 60-228
Publication No. 15 discloses a technology that controls the gain of the AGC circuit while a signal is being received and writes data into the memory, and reads data from the memory when the signal is cut off. The optical signal is based on the assumption that the received signal level when the signal is present does not change in a short period of time. Depending on the audio signal in which a sound signal and a silent signal appear, there will be signal interruptions, so when applied to audio signals, the calculation of the gain value will be interrupted every time the signal interruption occurs for a short period of time, which is characteristic of audio signals. However, since the signal level of a new sound section is not necessarily the same as the level of the previous sound section, a step change occurs in the control output calculated based on this, making it difficult to maintain stable gain control. cannot be done.

The present invention was made in order to solve the above-mentioned problems, and provides a digital AGC device that can generate a stable gain so that the target audio data as an input signal undergoes more natural level adjustment. The purpose is to obtain.

[Means to solve the problem]

A digital AGC device according to the present invention includes a multiplier that multiplies a digital signal obtained by converting an analog input signal of an acoustic signal into a digital signal by an A/D converter by a predetermined gain coefficient, and a level that detects the output level of the multiplier. An automatic gain control loop consisting of a detection circuit, an averaging circuit that extracts an average value based on the detection level, and a gain coefficient generator that calculates a gain coefficient based on the average value and outputs it to the multiplier. In a digital automatic gain control device equipped with the above-mentioned system, the control target is an acoustic signal whose amplitude constantly changes significantly and where sound and silence appear in a short period of time, and determines whether the digital signal is sound or silence. control to obtain an average value in a time period larger than at least one wavelength, and to set the gain coefficient to be output to the multiplier based on the output of the audio detector as the previous sample value when the digital signal is silent; It is equipped with means.

[Effect]

The digital AGC device according to the present invention adds a voice detector for detecting voice to the AGC loop, and determines whether the voice, which is an input signal, is audible or silent.

Then, the control means ignores the input signal during the silent period, inputs the average output signal during the active period in place of it, takes the average, and uses the noise during the silent period as the target for calculating the coefficient for averaging. To avoid this, the gain given to the previous sample is maintained during silent sections. During averaging, the voice detector attached to the AGC loop examines the nature of the input signal and extracts only the voice, so noise in silent conditions can be ignored.
A stable gain commensurate with the input is given to the output signal.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1, in which the same parts as in FIGS. 3 and 4 are denoted 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 are the same as those in the conventional device shown in FIG. In this example, the AGC
An adder (4
2) and the delay circuit T, there is a selector device (64) and a switch (64) for switching the circuit between sound and silent states.
65) and separately set the noise threshold C,
A comparator (63) is provided to compare this threshold value C with the input signal of voice, and the comparator (63) is used to switch the circuit between the time of sound and the time of no sound. Note that a multiplier (67) for weighting I/a is provided between the delay circuit T and the selector device (64).

Next, the operation will be explained in detail. The digital AGC device according to the present invention converts the analog audio input signal Aln into an A/D converter, similar to the conventional digital AGC system.
After converting into digital signal X by converter (1), A
In parallel with the processing within the GC loop, the following digital arithmetic processing is performed.

That is, the level of the digital output signal
2 and then weighted by b' in a multiplier (66). At this time, the time constant of the delay circuit T2 is sufficiently smaller than that of the delay circuit TI in the AGC loop, but is sufficient to detect the instantaneous level of the audio signal. Thereafter, a comparator (63) compares the data with a noise threshold value C that has been set separately, and determines whether the data is voiced or silent. This result is sent to a selector device (64) provided between the adder (42) and the delay circuit TI. The selector device (64) connects the switch (65) to the ON side when the input signal X is sound based on the output of the comparator (63), thereby forming a loop and performing averaging. Also, when X is determined to be silent, switch (65
) 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 gain value at each location when each automatic gain control method is applied to the input signal. A) is the input signal, A) is the input signal A), which is integrated by the adder (62) and the delay circuit 2 after square detection by the square circuit (61), and C) is the conventional signal for the input signal A). Similarly, 2) shows the gain generated by the AGC device to which the present invention is applied. As can be seen from this figure, the gain generated by the AGC device to which the present invention is applied has small fluctuations.

Therefore, even if there are turning points or silences during the call,
In the circuit that performs averaging, processing is performed by excluding this from the averaging target, so that a stable average value can be obtained even if the input signal is audio data with large level fluctuations.

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

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

〔Effect of the invention〕

As described above, according to the present invention, by detecting the voice within the AGC loop, it becomes possible to process the input signal during the silent period, and the output level increases more than necessary at the onset of the sound after the silent period. This has the effect that a stable gain can be given to the audio signal level without raising the audio signal level, and more natural audio signal level adjustment can be performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 explains gain values generated for input signals in a conventional digital AGC system and a digital AGC system when the present invention is applied. FIG. 3 is a system diagram showing an overview of a conventional digital AGC system, and FIG. 4 is a block diagram showing the hardware of FIG. 3. (31) and (32) are the squaring circuit and adder (41), (42) that constitute the level detection circuit, and T+ is the multiplier, adder, and delay circuit (51) that constitute the averaging level detection circuit. 52) are multipliers, adders, and delay circuits (61), (62), (83), (6B) that constitute the automatic gain control coefficient generation section.
, T2 is a squaring circuit, an adder, a comparator, a multiplier and a delay circuit (64) which constitute a voice detector, ([i5) is a selector device which constitutes a control means, and a switch AL is an automatic gain control loop. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A multiplier that multiplies a digital signal obtained by converting an analog input signal of an acoustic signal into a digital signal by an A/D converter by a predetermined gain coefficient, a level detection circuit that detects the output level of this multiplier, and a level detection circuit that detects the output level of the multiplier. A digital automatic gain control device comprising an automatic gain control loop consisting of an averaging circuit that extracts an average value, and a gain coefficient generator that calculates a gain coefficient based on the average value and outputs it to the multiplier, The amplitude of the control target changes significantly at all times,
and a sound detector that determines whether the digital signal is audible or silent, which targets an acoustic signal in which sound and silence appear within a short period of time; 1. A digital automatic gain control device comprising control means for setting a gain coefficient to be output to the multiplier based on the output of the audio detector as a pre-sampled value when the signal is silent.