JPH0258430A - Adaptive quantizer - Google Patents

Abstract

PURPOSE:To attain a satisfactory quantizer adaptive control without depending on the type of an input signal by adapting to the type of an input signal and setting the adaptive speed of the quantizer. CONSTITUTION:A speed control parameter calculating circuit is composed of an estimation function 11, a leak integrator 12, a comparator 13 and a limiter 14. When an input is a sound signal, since a level fluctuation is severe, a quantizing value I becomes a smooth distribution over the wide range. On the other hand, when the input is a MODEM signal, since the level in the stationary condition is approximately constant, the distribution of the quantizing value I becomes steep with a certain value as a center. Then, by an estimation function 11 to display the difference in the distribution condition of the quantizing value of the sound signal and the MODEM signal, it can be known whether the input signal is the sound signal or the MODEM signal. Consequently, by using the estimation function 11, the speed control parameter can be applied and set to the input signal. Thus, the optimum adaptive quantization can be executed for the input signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is based on an adaptive differential PCM coding method (hereinafter referred to as ADPCM).
The present invention relates to adaptive quantizers used in systems such as quantizers and the like, and particularly to encoders and decoders suitable for both voice and modem signals.

[Conventional technology]

On the nine ADPCM methods, I.E.E.
Cloval, Telecomuniage, J/Z, Conference (1984), pp. 23.1@1 to 23-1.
・4 pages (IEgE GL, 0BAL'rELECOM
U-NICATIONS C0NFEtRENC:E
1984. As discussed in pp. 23.1.1-23.1.4), as a method of changing the speed of adaptation of the quantizer, the speed control of the fast adaptive variable 9 for voice and the slow adaptive variable yl for modem is used. DLQ (Dynamia Locking Qu
antizsr) is adopted.

That is, the quantizer adaptation variable y is y(k+1)=a, (k)yu(k-1)+(1-a
□0))y, (k-1) given by, al, o<a
In Step 1, when a modem signal is input, the quantizer adaptation variable is selected such that when the modem signal is input, the quantizer adaptation variable is controlled such that when the modem signal is input, the quantizer adaptation variable is 1, and when the audio signal is input, the quantizer adaptation variable is 0.

FIG. 5 shows a block diagram of the above-mentioned a generator circuit.
From the child value I (k), Ili F (I), which indicates the magnitude of the prediction residual signal that is the input signal of the quantizer, is calculated by circuit 2.
The sixth stage short-time leak integration circuit 22 generated by 1
F (short-time average of IJ + 11 d,, (k) t,
The long-term leak integration circuit 23 installed in parallel with the circuit 22
Calculate the long-term average value d1.11(k) of (I).

Then, in the comparison circuit 24, dl, l#(k) and dml
(k) and speed control parameter history trfG′ft, I dos (k)−dml (
k) I < αdml (when kJ G=OI dm
s (k) del(k) l > αdml (k)
Calculate as Q, ≦1 (α is a constant). Next, according to the further 1iFrta, the speed control parameter a p
(k), and the limiter circuit 26 calculates the calculated value a.

The speed control parameter al is calculated by limiting 0≦a and ≦1.

[Problem to be solved by the invention]

In the conventional technology, the speed control parameter is generated based on the magnitude of the prediction residual signal.
When it is difficult to distinguish the prediction residual signal from a voice signal due to changes in the magnitude of the prediction residual signal, such as a ps modem signal, the speed control parameter cannot be set to match the input signal, so the quantizer adaptive variable is used as the input signal. There is a problem in that it is not optimal for the signal and bit errors occur.

The object of the present invention is to provide a speed converter adapted to the input signal when the input signal is an audio signal or a modem signal.
An object of the present invention is to provide an adaptive quantizer that can generate an a-rule parameter and perform optimal adaptive quantization on an input signal.

[Failure to solve the problem]

The above object is achieved by providing an evaluation function that represents the difference in the distribution state of quantization values of the audio signal and the modem signal, and generating the speed control parameter update t by outputting the function value. In other words, the adaptive quantizer includes an evaluation function according to the probability of appearance of the quantizer output value and a means for integrating the function output t, and when the adaptation is slow, the changes in the input signal and the predicted signal are reversed. This is achieved by providing a means for suppressing the adaptive speed to follow the increase in the difference signal that occurs due to the increase in the difference signal and maintaining the state of the adaptive quantizer.

[Effect]

When the input is an audio signal, the level fluctuations are large, so
The quantization weight has a smooth distribution over a wide range. On the other hand, when the input is a modem signal, since the level Vill in the steady state ta4 is approximately constant, the distribution of the quantization direct weight takes a sharp turn around a certain value.

Therefore, it can be determined whether the input signal is an audio signal or a modem signal using an evaluation function that represents the difference in the distribution state of quantized values between the audio signal and the modem signal. Therefore, by using this evaluation function, it becomes possible to set the speed control parameter in accordance with the input signal.

[Implementation row]

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 1 is a block diagram of a speed control parameter calculation circuit for an adaptive quantizer according to an embodiment of the present invention. This speed control parameter calculation circuit includes an evaluation function 11, a leak integrator 12, a comparator 13, and a limiter 14.

ADPCM quantization value 1 (k
)'? , ff(a[al i Kj ref exchange, H(l
Calculate I(k)l). The H(I I(k)l
) is +11<a III>b when H(III)≦
1 ■a<III<b H(III)≦
This is a function that takes a value such as 0 (2), and an example of this is shown in FIG.

Next, the output H(II(k)l) is integrated by the leakage integrator 12. FIG. 4 shows a block diagram of the leakage integrator. 51 is an adder, 52 is a multiplier, and 56 is a delay device. β is a leakage multiplier, and a number between 0 and 1 is sufficiently close to 1, and a number smaller than 1 is used.

When the input signal is an audio signal, I (k) I has a distribution as shown in the broken line in Figure 2, so compared to when the input signal is a modem signal (solid line in Figure 2), H( l I(k
)l) causes the above-mentioned (■) to occur more often. Therefore, H(l
The leakage integral (direct d(k) of I(k)I) tends to be d(k) → 2 when an audio signal is input, and d(k) → 0 when a modem signal is input. Therefore, the leakage integral value is circuit 13
When d(k)>δ, G(k)=1 (during voice input)
d(k) (when δ, G(k) = 0 (at modem input), calculate G(k)', perform leakage integration again in circuit 12, and limit the speed by circuit 14. Calculate the control parameter a (kl).

The high-speed adaptive variable yu for voice and the low-speed adaptive variable y for modem
, (k) are linearly combined from the above speed control parameter a to (k) K, and y(k) = a, *yu(k) + (1-a, ) y
, (k) quantizer adaptation variable)'(k)f! :calculate.

The speed control parameter obtained as described above is controlled to be the average value of the parameter changes that occur over several samples by performing leakage integration, so even if a line error or the like occurs, the state of the speed control parameter remains unchanged. is not immediately reversed, and the code/decoders are not controlled with different adaptation parameters.

〔Effect of the invention〕

According to the present invention, the adaptive speed of the quantizer can be set in accordance with the type of input signal, so that excellent adaptive control of the quantizer can be performed regardless of the type of input signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a speed control parameter calculation circuit of an adaptive quantizer according to an embodiment of the present invention;
Fig. 2 is a distribution graph of quantization values of audio signals and modem signals, Fig. 3 is a characteristic diagram of an example of an evaluation function, Fig. 4 is a detailed block diagram of the leakage integrator shown in Fig. 1, 5
The figure is a block diagram of a speed control parameter calculation circuit of a conventional adaptive quantizer. 11... Evaluation function 12... Leak integrator 13... Comparator 14... Limiter 51... Adder 52... Multiplier 53... Delay device.

Claims (1)

[Claims] 1. Means for quantizing a difference signal obtained by subtracting a predicted signal of the input signal from a digitized input signal input at each sampling time using an adaptive quantizer, means for generating a high-speed adaptive variable, and a low-speed In an adaptive quantizer having a means for generating an adaptive variable, an evaluation function according to the probability of occurrence of the output value of the quantizer, a means for integrating the function output, and an input signal and a prediction signal when the adaptation is slow. 1. An adaptive quantizer comprising means for suppressing adaptation speed tracking and maintaining the state of the adaptive quantizer in response to an increase in the difference signal caused by the opposite change direction of the adaptive quantizer.