JPH0732338B2 - Automatic gain control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to voice addition (mixing) in a telephone line.
The present invention relates to a digital automatic gain control device used for audio signal processing such as audio level adjustment.

[Conventional technology]

In recent years, the development of the communication field has been remarkable, and many new products have been produced. For example, by maintaining multiple terminals, it is possible to leave a voice message even if the people on the receiving side are absent, or a video conference system that allows people who are far from each other to hold a conference without moving. Voice mail devices and the like are a prominent example of this, which saves time wherever possible. These new inventions play a large role in a busy urban society, and they are of great interest 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. Auto-matic 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. Furthermore, at present, many digital signal processing process systems implement digital AGC circuits, and AGC devices for more limited purposes are being developed.

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

An example of a hardware implementation of the gain loop AL in FIG. 3 is disclosed in Japanese Patent Publication No. 63-19089 as shown in FIG. 4, for example. Hereinafter, the operation of FIG. 4 will be described in detail.

The input audio signal Ain is converted to the digital signal X by the A / D converter (1) and then given to this circuit. The digital signal X is first input to the multiplier (2), where it is multiplied by the gain coefficient Ag to calculate the gain output signal y. The digital output signal y is branched into the gain loop and first input to the adder (32) via 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 gain coefficient Ag is determined and generated.

[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, the fourth
In the figure, since the input voice signal has a wide amplitude range and has a property that it greatly fluctuates in a short time,
As described above, the signal is input to the AGC loop AL, and this level is calculated for each cycle, and the signal gain value is calculated based on this level.In the AGC loop, the value of the gain coefficient Ag differs for each sample, and the AGC Since the gain value given to the input signal by the system is not a stable value, it may give an unnatural feeling when listening to the reproduced sound.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to automatically generate a stable gain so that voice data as an input signal undergoes a more natural level adjustment during conversation. The purpose is to obtain a gain control device.

[Means for Solving the Problems]

An automatic gain control device according to the present invention detects a level of a multiplication output obtained by multiplying an input signal by a predetermined gain coefficient, extracts an average value based on the detected level, and outputs a new gain based on the average value. In an automatic gain control device having an automatic gain control loop having a gain coefficient generating section for calculating a coefficient, in the gain coefficient generating section, the difference between the calculated gain coefficient and the gain coefficient at the previous sample is set in a preset range. A comparison means for determining whether or not it is within the setting range and a gain coefficient at the time of pre-sampling when it is within the setting range, and when it is outside the setting range, a new gain calculated based on the extraction of the average value And a selection switching means for selecting a coefficient.

[Action]

In the automatic gain control device according to the present invention, in the gain coefficient generating section, it is determined by the comparing means whether or not the difference between the calculated gain coefficient and the gain coefficient at the time of the previous sample is within a preset range, and the selection is made. The hearing switching means selects the gain coefficient at the time of the previous sample when it is within the setting range, and selects the newly calculated gain coefficient when it is outside the setting range.

〔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,
(1) to (5), (31), (32), (41), (42),
(51), (52) and T ₁ are the same as those of the conventional device shown in FIG. In this embodiment, the difference from FIG. 4 is that the difference between the gain coefficient calculated by the adder (52) and the gain coefficient at the time of the previous sample from the delay circuit T ₂ is displayed in the gain coefficient generator (5). An adder (53) to be obtained, an absolute value circuit (54) for converting the addition output into an absolute value, and a comparator (55) for determining whether or not the output is within a preset upper and lower limit range Wf. , The gain coefficient at the time of the previous sample in the delay circuit T ₂ is selected based on the command of the time comparator (55) within the setting range, and the switch is switched to the off side so as to be applied to the multiplier (2), and the setting is performed. When it is out of the range, a switch circuit (56) for switching the switch to the ON side is provided to select the gain coefficient newly calculated by the adder (52) and give it to the multiplier (2).

Next, the operation will be described in detail. The automatic gain control device in this embodiment, like the conventional digital AGC device, converts an analog voice input signal Ain into a digital signal X by an A / D converter and then inputs it into an AGC loop to sequentially perform digital arithmetic processing. Is going to be. Now n
It is assumed that the digital signal Xn having the th sample value is input to the AGC loop. The same processing as in the conventional example is performed until it is input to the gain coefficient generator (5). After that, it is input to the gain coefficient generator (5), and the following processing is subsequently performed. That is, while the input digital signal Xn goes around the AGC loop, the adder (5
The gain coefficient Agn is calculated according to 2). Add this (53)
, And the gain factor given to the previous sample Xn ₋₁ ,
That is, the difference from the gain coefficient Agn ₋₁ input to the adder (53) via the delay circuit T ₂ is calculated. The output of the adder (53) is continuously input to the comparator (55) through the absolute value circuit (54) that takes the absolute value. Then, it is compared with a reference value wf that is separately set as a width that ignores the gain variation. Two values here
When the difference between Agn and Agn _-1 is larger than wf, the switch circuit (50) is connected to the ON side, the gain coefficient is rewritten with a new value, and the gain coefficient becomes Agn. On the contrary, when the difference is smaller than wf, the switch circuit (56) is connected to the OFF side, and the gain coefficient Agn _-1 for the current sample is given from the delay circuit T ₂ .

FIG. 2 shows waveforms at various parts. When an audio signal as shown in (a) is input, the value output from the adder (52) (FIG. 2 (b)), the output signal of the adder (53). ((C) in the figure), a signal generated by the comparator (55) for switching the switch circuit (56) ((d) in the figure, a gain value Ag output from the gain coefficient generating section (5) As can be seen from this figure, a stable gain can be obtained from the AGC circuit to which the present invention is applied, ignoring minute fluctuations.

Therefore, a stable gain is ensured even in the transmission of voice,
The effect is that a natural call can be made on a telephone line or the like.

In the above embodiment, a circuit for ignoring minute fluctuations within a certain reference value is provided in the gain coefficient generating section (5).
Alternatively, if the average value based on the newest data provided in the averaging circuit (4) has a small difference from the average value referred to when calculating the above-mentioned gain value, it can be ignored even if it is ignored. Has the effect of.

Further, in the above-described embodiment, the operation centering on the hardware processing is performed, but instead of this, it is also possible to perform the software processing centering on the processor.

〔The invention's effect〕

As described above, according to the present invention, a stable gain can be obtained by ignoring a minute fluctuation of the continuous gain value calculated by a predetermined calculation each time the AGC loop makes one round. As described above, there is an effect that a stable gain can be obtained even when the amplitude range is largely changed in a short time as a control target.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a digital type AGC device, FIG. 2 is an output waveform diagram of each part of FIG. 1, FIG. 3 is a system diagram showing an outline of a conventional digital gain system, and FIG. It is a block diagram which shows FIG. 3 by hardware. (31) and (32) are squaring circuits and adders that compose the level detection circuit (3) (41), (42), and T ₁ are multipliers, adders, and delay circuits that compose the averaging circuit (4). (51) to (56), T ₂ are sequentially gain control coefficient generating section (5)
The automatic gain control loop includes a multiplier, an adder, an adder, an absolute value circuit, a comparator, and a switch circuit and a delay circuit AL, which are included in FIG.

Claims (1)

[Claims] 1. A gain for detecting a level of a multiplication output obtained by multiplying an input signal by a predetermined gain coefficient, extracting an average value based on the detected level, and calculating a new gain coefficient based on the average value. In an automatic gain control device having an automatic gain control loop having a coefficient generation unit, whether the difference between the calculated gain coefficient and the gain coefficient at the previous sample is within a preset range in the gain coefficient generation unit. Selection means for determining whether or not, and selecting a gain coefficient at the time of pre-sampling when it is within the setting range, and selecting a new gain coefficient calculated based on the extraction of the average value when it is outside the setting range. An automatic gain control device comprising a switching means.