Speech coding system utilizing a recursive computation technique for improvement in processing speed

Abstract

This invention provides a novel speech coding system which recursively executes a filter-applied "Toeplitz characteristic" by causing a drive signal (i.e., an excitation signal) to be converted into a "Toeplitz matrix" when detecting a pitch period in which distortion of the input vector and the vector subsequent to the application of filter-applied computation to the drive signal vector in the pitch forecast called either "closed loop" or "compatible code book" is minimized. The vector quantization method substantially making up the speech coding system of the invention is characteristically used by the system.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a vector quantization system made available for compression and transmission of data of digital signals such as a speech signal for example. More particularly, the invention relates to a speech coding system using a vector quantization process for quantizing a vector by splitting the vector into data related to gain and index.2. Description of the Related ArtToday, the vector quantization system is one of the most important technologies attracting keen attention of those concerned, which is substantially a means for effectively encoding either a speech signal or an image signal by effectively compressing it. In particular, in the speech coding field, either the "code excited linear production (CELP)" system or the "vector excited coding (VXC)" system is known as the one to which the vector quantization system is applied. Further detail of the CELP system is described by M. R. Schroeder and B. S. Ata...

AI Technical Summary

Benefits of technology

The object of the invention is to provide a speech coding system which is capable of fully solving those problems mentioned above by minimizing the amount of computation to a certain level at which real-time data processing operation can securely be executed with a digital signal processor.

The second object of the invention is to provide a vector quantization system which is capable of securely quantizing stable and high quality vectors notwithstanding the procedure of quantizing the gain after selecting an optimal index.

When executing the pitch-forecasting process called "closed loop" or "compatible code book", the invention converts the drive signal matrix into "toeplitz matrix" to utilize the "Toeplitz characteristic" so that the filter-applied computation can recursively be accelerated, thus making it possible to sharply decrease the required rounds, i.e., number of time of multiplication.

The second function of the invention is to cause the speech coding system to identify whether the optimal gain exceeds the critical value or not by applying the vector power generated from the prospective index, the inner product value of the target vector, and the critical value of the gain of the preliminarily set vector. Based on the result of this judgment, the speech coding system specifies the prospective indexes, and then selects an optimal index by eliminating such prospective indexes containing a substantial error of the quantized gain. As a result, even when quantizing the gain after selecting an optimal index, stable and high quality vector quantization can be provided.

Problems solved by technology

Nevertheless, any of these conventional systems has a particular problem in the performance of quantization.

If this occurs, since the overall error of the quantized vector is extremely large, any conventional vector quantization process cannot provide quantization of stable vectors at all.

Consequently, when the error grows itself beyond the negligible range after execution of subsequent quantization of the gain, overall error of the quantized vector significantly grows.

As a result, any conventional system cannot provide quantization of stable vectors.

As is clear from the above description, when detecting pitch period by applying "detection of code book" and "closed loop or compatible code book" under the conventional CELP system, a huge amount of multiplication is needed, thus raising a critical problem when executing real-time data processing operations with a digital signal processor DSP.

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