JPH03132207A - Automatic gain controller - Google Patents

Abstract

PURPOSE:To obtain a stable gain by providing a comparison means to find whether or not a difference between a calculated gain coefficient and a gain coefficient in preceding sampling is within a range set in advance, and a selection means to select the gain coefficient corresponding to a comparison result at a gain coefficient generating part. CONSTITUTION:The gain coefficient generating part 5 is equipped with an adder 53 which finds the difference between the gain coefficient calculated with an adder 52 and that in the preceding sampling from a delay circuit T2, an absolute value circuit 54 which makes the above calculated output into an absolute value, and a comparator 55 which finds whether or not the output is within the range Wf between upper and lower limits set in advance. Also, it is equipped with a switching circuit 56 which performs the switching of a switch to an off side to select and supply the gain coefficient in the preceding sampling in the delay circuit T2 to a multiplier 2 based on a command from the comparator 55 when the output is within a set range, and also, selects the gain coefficient calculated newly with the adder 52 and performs the switching of the switch to an on side to supply it to the multiplier 2 when it is outside the set range. Thereby, the stable gain can be obtained.

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 for 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. A TV conference system that allows you to
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
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 also used in signal processing and has greatly contributed 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 to which AGC should be applied ^t
n is converted into a digital signal X by an A10 converter (1), which digital signal X is input into the AGC loop AL of the digital AGC system. Here, the signal enters the multiplier (2), where the gain coefficient is multiplied by g, resulting in the AGC output y, that is, y-8g-X. Output y is branched to level detection circuit (3) and averaging circuit (4)
It then enters the gain coefficient generator (5). Here, the gain coefficient g is changed to each output y by going around the gain loop AL.
Determined each time.

As an example of hardware implementation of the gain loop AL in FIG. 3, as shown in FIG. 4, for example,
There is one shown in Japanese Patent Publication No. 19089/1989.

The operation shown in FIG. 4 will be explained in detail below.

The input audio signal ^1o is converted into a digital signal X by the ^/D converter (1) and then applied to this circuit. The digital input signal
is calculated. The digital output signal y is branched into a gain loop and first a squaring circuit (3
1) is input to the adder (32). However, it is input to the adder (32) as a negative input. A reference value Dr is separately applied to the adder (32), and when the output y exceeds D, it is used as a negative input, and conversely, when y exceeds Or
When it is less than , it is given as a positive input to the multiplier (41), and given a certain weight (weighting coefficient a). The adder (42) and delay circuit T1 including this multiplier (41) perform averaging. Note that 1 and 0 for the b1 adder (52) for the multiplier (51) are both related to weighting, and g is determined and generated for the gain coefficient here.

(Problems to be Solved by the Invention) Since the conventional digital AGC device is configured as described above, it has the following problems. That is, in FIG. 4, the audio signal that is the input target has a wide range of amplitude and has a characteristic that fluctuates greatly in a short period of time. In the AGC loop, which calculates this level each time it is input and calculates the signal gain value based on it, the value of 8 to the gain coefficient differs for each sample, and the gain value that the AGC system gives to the input signal is stable. Since it is not a value, it may give an unnatural feeling when listening to the reproduced sound.

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

[Means to solve the problem]

The automatic gain control device according to the present invention detects the level of a multiplication output obtained by multiplying a human input signal by a predetermined gain coefficient, extracts an average value based on the detected level, and calculates a new gain based on the average value. In an automatic gain control device equipped with an automatic gain control loop having a gain coefficient generation section that calculates a coefficient, the gain coefficient generation section has a preset range for the difference between the calculated gain coefficient and the gain coefficient at the time of the previous sample. a comparison means for determining whether or not it is within the set range, and a gain coefficient at the previous sample when it is within the set range, and a new gain calculated based on the extraction of the above average value when it is outside the set range. and selection switching means for selecting coefficients.

(Function) In the automatic gain control device according to the present invention, in the gain coefficient generation section, the comparison means determines 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. The selection switching means selects the gain coefficient of the previous sample when it is within the set range, and selects the newly calculated gain coefficient when it is outside the set range.

〔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.
1) to (5), (31), (32), (41).

(42), (51), (52) and T1 are the same as those in the conventional device shown in FIG. In this embodiment, the difference from FIG. 4 is that the gain coefficient generator (5)
, the gain coefficient calculated by the adder (52) and the delay circuit T.

An adder (
53) and an absolute value circuit (5
4) and its output is within the preset upper and lower limit range If
A comparator (55) that determines whether or not it is within the set range, and a delay circuit T based on the command of the comparator (55) when it is within the set range.
The switch is switched to the off side to select the gain coefficient at the previous sample within and give it to the multiplier (2), and when the gain coefficient is outside the setting range, the gain coefficient newly calculated by the adder (52) is selected. The point is that a switch circuit (56) is provided which switches the switch to the on side so as to selectively apply the signal to the multiplier (2).

Next, the operation will be explained in detail. Similar to the conventional digital AGC device, the automatic gain control device in this embodiment converts an analog audio input signal ﾇ into a digital signal It performs arithmetic processing. The digital signal xn of the nth sample value is now A
Suppose that it is input to the GC loop. Gain coefficient generator (5)
Until it is input, the same processing as in the conventional example is performed.

Thereafter, the signal is input to the gain coefficient generating section (5), and the following processing is subsequently performed. That is, the input digital signal
While n goes around the AGC loop, the adder (52) calculates the gain coefficient Agn by the same process as in the conventional example. This is input to the adder (53) and the previous sample Xn-
1, that is, the difference from the gain coefficient ^gn-r inputted to the adder (53) via the delay circuit T2. The output of the adder (53) passes through an absolute value circuit (54) that takes its absolute value, and then passes through a comparator (55).
Enter. Then, it is compared with a reference value Wf that is separately set as a width for ignoring gain fluctuations. Here two values Ag
When the difference between n and ^gn-+ is larger than Wf, the switch circuit (56) is connected to the ON side, and the gain coefficient is rewritten to a new value and becomes Agn. Conversely, when the difference is smaller than If, the switch circuit (56) is connected to the OFF side, and the gain coefficient ^g for the current sample is
n-1 is given from delay circuit T2.

Figure 2 shows the waveforms of each part, and when the audio signal shown in (a) is input, the value output from the adder (52) ((b) in the same figure), the output signal of the adder (53) (Figure (c))
, a signal generated by the comparator (55) for switching the switch circuit (56) (see (d) in the figure), a gain coefficient generator (
5) The gain values Ag outputted from (e) in the same figure are shown respectively. As can be seen from this figure, the AGC circuit to which the present invention is applied can obtain a stable gain ignoring minute fluctuations.

Therefore, stable gain is ensured even in audio transmission,
This has the effect of allowing natural conversations to be made over a telephone line or the like.

Note that in the above embodiment, a circuit that ignores minute fluctuations within a certain reference value is provided in the gain coefficient generating section (5);
Alternatively, the averaging circuit (4) may be provided to ignore this when the average value based on the newest data has a smaller difference than the average value referred to when calculating the gain value. effective.

Further, in the above embodiment, the operation is performed mainly by hardware processing, but instead, it is also possible to perform the operation by software processing mainly by the processor.

〔Effect of the invention〕

As described above, according to the present invention, a stable gain can be obtained by ignoring small fluctuations in the continuous gain value calculated by a predetermined calculation each time it goes around the AGC loop, and thereby the audio signal This has the effect that a stable gain can be obtained even if the control target is something whose amplitude range fluctuates greatly in a short period of time.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an overview of a digital AGC device,
's2 diagram is an output waveform diagram of each part in Figure 1, Figure 3 is a system diagram showing an overview of a conventional digital gain system, and Figure 4 is a diagram showing the output waveform of each part in Figure 1.
The figure is a block diagram showing the hardware of FIG. 3. (31), (32) are the squaring circuit and adder (41), (42) that constitute the level detection circuit (3), and the multiplier, adder, and delay circuit that constitute the averaging circuit (4). (51) to (56), T2 is sequentially a multiplier, an adder, an adder, an absolute value circuit, a comparator, and a switch circuit and a delay circuit AL are automatic gain control which constitute the gain control coefficient generation section (5). In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] It has a gain coefficient generation unit that detects the level of the multiplication output obtained by multiplying the input signal by a predetermined gain coefficient, extracts an average value based on the detected level, and calculates a new gain coefficient based on the average value. In an automatic gain control device equipped with an automatic gain control loop, the gain coefficient generation section includes a comparison means for determining whether a difference between the calculated gain coefficient and the gain coefficient at the time of the previous sample is within a preset range. and selection switching means for selecting the gain coefficient at the time of the previous sample when it is within the set range, and selecting a new gain coefficient calculated based on the extraction of the average value when it is outside the set range. An automatic gain control device characterized by: