Data processing: speech signal processing – linguistics – language – Speech signal processing – For storage or transmission
Reexamination Certificate
1998-11-25
2001-09-11
Dorvil, Richemond (Department: 2641)
Data processing: speech signal processing, linguistics, language
Speech signal processing
For storage or transmission
C704S219000, C704S220000
Reexamination Certificate
active
06289307
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a codebook preliminary selection device, a codebook preliminary selection method and a storage medium storing a codebook preliminary selection program, for use in speech signal coding.
2. Description of the Related Art
In order to satisfy the requirements for increased capacity and reduced power consumption for mobile communication system, such as automobile telephone systems, standardization for low bit rate speech signal coding has been developed. The PSI-CELP (Pitch Synchronous Innovation-Code Excited Linear Prediction) is one of such well known standards. In PSI-CELP, 3.45 kbit/s is used for speech coding. In the speech coding, various processes, such as noise canceling, LSP quantization, power quantization, adaptive/fixed codebook searching and stochastic codebook searching, are carried out. This technique is introduced, for example, in the following literature:
Pitch Synchronous Innovation CELP (PSI-CELP)
—PDC half-rate speech CODEC—
Tomoyuki Ohya and collaborators
The Institute of Electronics, Information
and Communication Engineers
Technical Report of IEICE, RCS93-78, 1993-11
In the PSI-CELP, vocal tract information and excitation source information are encoded separately and then multiplexed to form a total code for a speech signal. Specifically, for encoding an input speech signal, LPC (Linear Predictive Coding) is first performed to obtain LPC parameters (coefficients) which represent the vocal tract information. The excitation source information is encoded, for example, through vector quantization of LPC predictive errors and stored in codebooks, such as an adaptive codebook, in the form of excitation code vectors with corresponding indices. When encoding the excitation source information of the input speech signal, the adaptive codebook is searched in the following manner: Specifically, the code vectors stored in the adaptive codebook are selected individually and inputted into an LPC synthesis filter so as to obtain synthetic speech signals. The synthetic speech signals are compared with the input speech signal individually so that such a code vector that minimizes a perceptual error between the synthetic speech signal and the input speech signal is finally selected as optimally representing the excitation source information of the input speech signal.
In the foregoing technique, however, there has been the following problem:
Specifically, the foregoing codebook searching requires repetition of calculations using the input speech signal and a large number of excitation code vectors, thus resulting in enormous amounts of calculations. In view of this, the foregoing literature introduces a technique of preliminary selection so as to reduce the amount of calculations. In the preliminary selection technique, simple evaluation values for all the candidates (code vectors) stored in the codebook are derived and then high-ranking X candidates are selected based on these simple evaluation values. However, for selecting the high-ranking X candidates, calculations of comparison of approximately (all the candidates×X) times are required. This calculation amount is not negligible and impedes load reduction and increased speed of a processing unit.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an improved codebook preliminary selection device.
It is another object of the present invention to provide an improved codebook preliminary selection method.
It is another object of the present invention to provide a storage medium storing an improved codebook preliminary selection program.
According to one aspect of the present invention, there is provided a codebook preliminary selection device comprising a synthesis filter that receives code vectors from a codebook and outputting synthetic signal vectors, respectively; a simple evaluation value deriving section that repeatedly executes matrix calculations based on a simplified calculation equation using an impulse response matrix of the synthesis filter, the code vectors from the codebook and gains of the code vectors inputted into the synthesis filter, so as to derive simple evaluation values, respectively, for evaluating errors between the synthetic signal vectors outputted from the synthesis filter and a target signal vector, respectively; a grouping section that divides the simple evaluation values into as many groups as the number of the simple evaluation values to be selected as candidates; and a preliminarily selecting section that compares the simple evaluation values mutually in each group to select the optimum value in each group and outputting the optimum values from all the groups as the candidates.
According to another aspect of the present invention, there is provided a codebook preliminary selection device comprising a synthesis filter receiving code vectors from a codebook and outputting synthetic signal vectors, respectively; a simple evaluation value deriving section repeatedly executing matrix calculations based on a simplified calculation equation using an impulse response matrix of the synthesis filter, the code vectors from the codebook and gains of the code vectors inputted into the synthesis filter, so as to derive simple evaluation values, respectively, for evaluating errors between the synthetic signal vectors outputted from the synthesis filter and a target signal vector, respectively; a grouping section dividing the simple evaluation values into as many groups as equal to or less than the number of the simple evaluation values to be selected as candidates; and a preliminarily selecting section comparing the simple evaluation values mutually in each group to select a given number of the high-ranking values in each group and outputting the high-ranking values from all the groups as the candidates.
It may be arranged that the given number of the high-ranking values is one when the number of the groups is equal to the number of the simple evaluation values to be selected, and more than one when the number of the groups is less than the number of the simple evaluation values to be selected.
According to another aspect of the present invention, there is provided a codebook preliminary selection method comprising the steps of, for evaluating errors between synthetic signal vectors outputted from a synthesis filter based on code vectors from a codebook and a target signal vector, respectively repeatedly executing matrix calculations based on a simplified calculation equation using an impulse response matrix of the synthesis filter, the code vectors from the codebook and gains of the code vectors inputted into the synthesis filter, so as to derive simple evaluation values, respectively; dividing the simple evaluation values into as many groups as equal to or less than the number of the simple evaluation values to be selected as candidates; and comparing the simple evaluation values mutually in each group to select a given number of the high-ranking values in each group and outputting the high-ranking values from all the groups as the candidates.
According to another aspect of the present invention, there is provided a storage medium that stores a program which is executable by a computer, the program allowing the computer to execute the steps of, for evaluating errors between synthetic signal vectors outputted from a synthesis filter based on code vectors from a codebook and a target signal vector, respectively, repeatedly executing matrix calculations based on a simplified calculation equation using an impulse response matrix of the synthesis filter, the code vectors from the codebook and gains of the code vectors inputted into the synthesis filter, so as to derive simple evaluation values, respectively; dividing the simple evaluation values into as many groups as equal to or less than the number of the simple evaluation values to be selected as candidates; and comparing the simple evaluation values mutually in each group to select a given number of the high-ranking values in each
Armstrong Angela
Dorvil Richemond
OKI Electric Industry Co., Ltd.
Rabin & Champagne, P.C.
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