Encoding and decoding apparatus of LSP (line spectrum pair) parameters

Abstract

An encoding and decoding apparatus quantizes LSP (Line Spectrum Pair) parameters, which are characteristics parameters of spectrum information included in a voice signal, with high accuracy and stability. This encoding and decoding apparatus comprises a first quantizer in which quantization is performed independently in the unit of one frame, and a second quantizer which uses a correlation between adjacent frames. An error comparator compares quantization errors produced by the first quantizer and quantization errors produced by the second quantizer to select the one quantizer whose quantization errors are less than that of the other quantizer. The first quantizer produces a highly accurate quantization with stability regardless a condition of an input voice signal, while the second quantizer produces a highly accurate quantization when input voice signal stays quasi-stationary. By switching these two quantizers, this apparatus can offer stable and highly accurate quantization regardless of the condition of the input voice signal.

Description

[0001]This is a Reissue application of U.S. Pat. No. 5,802,487, issued Sep. 1, 1998.FIELD OF THE INVENTION[0002]This invention relates to an encoding and decoding apparatus of LSP parameters which are characteristic parameters of spectrum information included in voice signals.DESCRIPTION OF THE PRIOR ART[0003]A main stream of the voice encoding apparatus which handles a signal of which bit rate ranging from 4 to 8 kbps is to separate spectrum information from voice source information through analyzing a voice signal before encoding them. The LSP parameter is a characteristic parameter indicating spectrum information. The LSP parameter, in general, uses 10 dimensions / frame, and one of the most fundamental method for encoding the LSP parameter is to handle each individual value as a scalar for quantization. However, since this method produces rather low quantization effect, a vector quantization which quantizes a plurality of LSP parameters in a mass is more frequently used. When util...

AI Technical Summary

Benefits of technology

[0011]The purpose of this invention is to overcome the problems entailed to the conventional apparatus: This invention offers an encoding and decoding apparatus of LSP parameters which can maintain a high accuracy of quantization even if an input voice signal is in transient state, and which also has higher resistance to errors.

Problems solved by technology

However, when an input voice signal is in transient state, predictive gain lowers and the accuracy of quantization also lowers.

This method is good at voice encoding when a frame length is short, but it does not produce a good result when a frame length is long.

Since the above conventional apparatus requires predicting a present value based on past quantized values, a code error produced in a transmission line influences not only the error frame but also the frames following.

The conventional apparatus is thus vulnerable to errors.

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