JPS59131226A - Adaptive quantizer - Google Patents

Abstract

PURPOSE:To obtain the quantizing characteristics having excellent adaptability to the signals of different statistic properties by switching coefficient tables in accordance with the features of the input signal. CONSTITUTION:The sample value ek of the input signal supplied from a terminal 1 in the form of a discrete time series is multiplied by 1/xk through a multiplier 2 and turned into zk'. This zk' is coded into In by a quantizer 3. While the adversely quantized value ek to an input ek is obtained by multiplying xk by the adversely quantized value zk of an adverse quantizer 4 through a multiplier 5. The xk is obtained by multiplying the coefficient value M(In-1) of a coefficient table 6 deciced by a 1-sample preceding code (In-1) or a coefficient table 10 for voice band data by (xBk-1) through a multiplier 8. This (xBBk-1) is obtained through raising to B through a 1-sample preceding (xk-1) power multiplier 7. A deciding circuit 11 extracts the features of the input signal, and this output S is used to perform switching between tables 6 and 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an adaptive decoder with excellent quantization characteristics even for time-series signals having different statistical properties.

(Background Art) Fig. 1 shows a conceptual diagram of an adaptive quantizer commonly used in the past. In Fig. 1, the sample value ek of the input signal input as a discrete time series from terminal 1 is multiplied Vessel 2
is multiplied by 1/Xk, becomes zk, and is converted by quantizer 3 to ■
. is encoded as . On the other hand, the dequantized value tk for the input ek is obtained by multiplying χ by the dequantized value zk of the dequantizer 4'
It is obtained by multiplying by unit 5.

As shown in equation (+), Xk is the sign In of the previous sample
-1, the coefficient value M(In-
+) and Xk-□, which is obtained by raising Xk-1 of the previous sample to the power of B in the exponentiation multiplier 7, by the multiplier 8.

xk = M (In-1) It had characteristics. However, there is a drawback that the quantization characteristics deteriorate for time-series signals having different statistical properties.

(Problem to be solved by the invention) The present invention creates a coefficient table according to an input signal in order to configure an adaptive quantizer whose quantization characteristics do not deteriorate even for time-series signals having different statistical properties. It has at least two juveniles and its Tehu.

This is based on the result of determining the output signal from the dequantized output signal.

(Structure and operation of the invention) FIG. 2 shows a first practical example of the invention. Portions 11 and 23 surrounded by dotted lines are circuits added to the conventional σ) circuit in FIG. 1, 10 is a coefficient table for Voice Band Data, 15 is a coefficient table for 6. A changeover switch 11 for changing over the IO coefficient table is a circuit that extracts the characteristics of the input signal and outputs a signal S for appropriately changing over the 6,100 coefficient tables according to the result.

FIG. 3 shows a second embodiment of the invention. In the figure, ℃・te,
Input the dequantized value ek to bandpass filters 15 and 16 whose center frequencies are near the 17th ormant frequency and near the carrier frequency of Voice Band Data, respectively,
The power of the output signals of the two filters is added to the accumulator 17゜18.
Calculate sequentially. Then, a comparator 19 successively obtains the ratio α of the two powers, and a successive determination circuit 20 determines the range of the value, and successively outputs a switching signal.

FIG. 4 shows a third embodiment of the invention. 20 is a sequential determination circuit, and 21 is a buffer circuit.

If the signal .alpha. contains noise, there is a risk that the sequential judgment circuit will be affected by the noise and may malfunction. Buffer circuit 21
This eliminates the influence of noise, uses a preset counter, and is configured to issue a table switching command only when preset conditions are met. When the circuit of FIG. 4 is added to FIG. 3, it is assumed that whether or not the circuit of FIG. 4 is operated and the number preset in the preset type counter can be arbitrarily set.

Audio signals with different statistical properties and Voice Band
There are two types of coefficient tables suitable for each type of data, and these tables can be switched appropriately depending on the input signal.
There is an advantage that a signal in which nd Data is sent in time series can be adaptively quantized.

(Effects of the Invention) Since the present invention has quantization characteristics with excellent adaptability to signals with different systematic characteristics, it is possible to transmit audio, image signals, and voice band data in time series. It can be used as a quantizer in cases.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of a conventional adaptive quantizer, FIG. 2 is a first embodiment of the present invention, FIG. 3 is a second embodiment of the present invention, and FIG. 4 is a third embodiment of the present invention. It is a conceptual diagram showing an example of. 1, 12.13.14... terminal 2, 5.8... multiplier 3... quantizer 4... dequantizer 6.10 ...Coefficient table 11 ... Judgment circuit 15, 16 ... Bandpass filter 17, 18 ... Accumulator 19 ... Comparator 20. ... Sequential judgment circuit 21 ... Buffer circuit Patent applicant Oki Electric Industry Co., Ltd. Patent application agent Kei Yamamoto - Fig. 1 Fig. 3 Fig. 4'

Claims (3)

[Claims] (1) In an adaptive quantizer that sequentially quantizes a correlated discrete input signal sequence according to the contents of a coefficient table that defines a quantization width, when the coefficient table is small (
1. An adaptive quantizer, characterized in that two types of adaptive quantizers are provided, and a determination circuit is provided for switching coefficient tables according to the characteristics of an input signal. (2) Claims in which the determination circuit inputs the dequantized output signal to at least two feature extraction filters, determines the ratio of their respective output powers, and switches the coefficient table according to the value range of the ratio. Adaptive quantizer according to paragraph 1. (3) The determination circuit inputs the dequantized output signal to two feature extraction filters, calculates the ratio of their respective output powers, and switches the coefficient table according to the instantaneous determination based on the value of the ratio; 2. The adaptive quantizer according to claim 1, wherein it is possible to arbitrarily set whether to switch the coefficient table when the instantaneous determination result continues a predetermined number of times.