Fixed sound source vector generation method and fixed sound source codebook

• US 20050228652A1
• Filed: 02/20/2003
• Published: 10/13/2005
• Est. Priority Date: 02/20/2002
• Status: Active Grant

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Nippon Telegraph and Telephone Corporation, Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Hiwasaki, Yusuke, Ehara, Hiroyuki, Yasunaga, Kazutoshi, Mano, Kazunori
• Granted Patent: US 7,580,834 B2
• Time in Patent Office: Days
• US Class Current: 704/219
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders

Abstract

At the speech encoding end, upon generation of an fixed excitation vector, the shape of an excitation vector output from pulse excitation codebook 301 is identified in pulse excitation vector shape identifier 302, a dispersion vector used for excitation vectors of the shape is output from dispersion vector storage 304, and, in dispersion vector convolution processor 303, dispersion vector convolution processing of the excitation vector is performed. In particular, when a pulse excitation vector having a specific shape of high frequency of use is output from pulse excitation codebook 301, pulse excitation vector shape identifier 302 controls dispersion vector storage 304 in such a way that an additional dispersion vector prepared dedicated to the pulse excitation vector is output. By this means, it is possible to provide a technology that improves the quality of decoded speech and that decodes speech more natural and audible to the user.

Claims

1. A method for generating a fixed excitation vector, said fixed excitation vector required in a CELP type speech encoder or a CELP type speech decoder, by convoluting a dispersion vector in a pulse excitation vector, said method comprising:

preparing a plurality of dispersion vectors;

selecting an optimum dispersion vector shape in accordance with a shape of an excitation vector; and

generating the fixed excitation vector by convoluting a selected dispersion vector in the excitation vector.

2. The method for generating a fixed excitation vector according to claim 1,

wherein a fundamental dispersion vector for common use for the pulse excitation vector, and an additional dispersion vector for use for a vector of a predetermined shape are prepared;

and

wherein the fixed excitation vector is generated using the fundamental dispersion vector or the additional dispersion vector.

3. A fixed excitation codebook that generates a fixed excitation vector by convoluting a dispersion vector in a pulse excitation vector, comprising:

means for selecting an optimum dispersion vector shape in accordance with a shape of an excitation vector from a plurality of dispersion vectors; and

means for convoluting a selected dispersion vector in the excitation vector.

4. The fixed excitation codebook according to claim 3,

wherein a dispersion vector storage is provided to store a fundamental dispersion vector for common use for the pulse excitation vector, and an additional dispersion vector for use for a vector of a predetermined shape;

and

wherein the fixed excitation vector is generated using the fundamental dispersion vector or the additional dispersion vector.

5. The fixed excitation codebook according to claim 4,

wherein a pulse excitation vector shape identifier is provided;

and

wherein, only when the pulse excitation vector is identified by said shape identifier to have the predetermined shape, the fixed excitation vector is generated using the additional dispersion vector.

6. The fixed excitation codebook according to claim 3, comprising:

at least two types of pulse excitation codebooks that output excitation vectors composed of different numbers of pulses or having different combinations of positions where a pulse can occur; and

a dispersion vector storage that stores dispersion vectors designed respectively dedicated to the pulse excitation codebooks.

7. A CELP type speech encoder having a fixed excitation codebook, said fixed excitation codebook comprising:

means for selecting an optimum dispersion vector shape in accordance with a shape of an excitation vector from a plurality of dispersion vectors; and

means for generating a fixed excitation vector by convoluting a selected dispersion vector in the excitation vector.

8. A CELP type speech decoder that receives an excitation gain code, an adaptive excitation vector code, and a fixed excitation vector code transmitted from the CELP type speech encoder of claim 7 and decodes speech, said CELP type speech decoder comprising:

quantization gain generating means that decodes an adaptive excitation vector gain and a fixed excitation vector gain specified by the excitation gain code;

an adaptive excitation codebook that takes one frame of samples as an adaptive excitation vector from past drive excitation signal samples specified by the adaptive excitation vector code;

a fixed excitation codebook that generates a fixed excitation vector specified by the fixed excitation vector code;

a drive excitation vector generating means that generates a drive excitation vector by adding a value obtained by multiplying the adaptive excitation vector gain on the adaptive excitation vector, and a value obtained by multiplying the fixed excitation vector gain on the fixed excitation vector;

high-frequency emphasis means that performs high-frequency emphasis processing on the drive excitation vector; and

a synthesis filter that performs filter synthesis of the drive excitation vector output from the high-frequency emphasis means using a filter coefficient.

9. The CELP type speech decoder according to claim 8, wherein said high frequency emphasizing means comprises:

a high pass filter that allows a high-frequency component of the drive excitation vector to pass;

a first log power calculator that calculates a log power of the drive excitation vector that passed the high pass filter;

an adder that performs processing that subtracts the drive excitation vector that passed the high pass filter from the drive excitation vector before passing the high pass filter;

a second log power calculator that calculates the log power of the drive excitation vector, from which the high component is removed, calculated by the adder;

a power ratio calculator that calculates a ratio between the log powers calculated by the two log power calculators; and

a coefficient calculator that calculates a value of a coefficient whereby the drive excitation vector that passed the high pass filter in such a way that the power ratio becomes a constant value,

wherein high-frequency emphasis processing is performed by multiplying a signal component that passed the high pass filter by the coefficient calculated by the coefficient calculator and adding a result thereof to the drive excitation vector.

10. A program that generates a fixed excitation vector by convoluting a dispersion vector in a pulse excitation vector, comprising the steps of:

selecting an optimum dispersion vector shape in accordance with a shape of an excitation vector from a plurality of dispersion vectors; and

convoluting a selected dispersion vector in the excitation vector.