Speech coding apparatus, speech decoding apparatus, speech coding and decoding method and a phase amplitude characteristic extracting apparatus for carrying out the method

• US 5,724,480 A
• Filed: 10/26/1995
• Issued: 03/03/1998
• Est. Priority Date: 10/28/1994
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Yamaura, Tadashi
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): Edouard, Patrick N.
• Application Number:
  US08/548,448
• Time in Patent Office: 859 Days
• Field of Search: 395/2.28, 395/2.29, 395/2.3-2.32, 395/2.16, 395/2.17
• US Class Current: 704/219
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
• CPC Class Codes: G10L 2019/0007 Codebook element generation

Abstract

A speech coding and decoding apparatus for improving the quality of synthesized speech. A coding portion includes a filter for adding a short-term phase amplitude characteristic to an excitation signal, and a coding circuit for quantizing and coding a phase amplitude characteristic. A decoding portion includes a decoding circuit for decoding the coded phase amplitude characteristic, and a filter for adding the same phase amplitude characteristic as that in the coding portion. Thus, it is possible to synthesize high-quality speech with good reproducibility of the phase amplitude characteristic of an excitation signal.

Claims

1. A speech coding apparatus comprising:

linear prediction parameter analysis means;

linear prediction parameter coding means;

excitation signal generating means;

a synthesis filter for synthesizing an output signal of said linear prediction parameter coding means and an excitation signal output from said excitation signal generating means;

phase amplitude characteristic coding means for quantizing and coding a short-term phase amplitude characteristic which is obtained by analyzing a linear prediction residual signal of input speech signal; and

a phase amplitude characteristic adding filter for adding said short-term phase amplitude characteristic to said excitation signal.

2. A speech coding apparatus according to claim 1, wherein said excitation signal generating means includes:

an adaptive codebook for outputting an adaptive vector;

a random codebook for outputting a random vector; and

an optimum code searching means for searching an optimum excitation; and

uses a pulse train as said random vector.

3. A speech coding apparatus according to claim 2, wherein a pulse interval of said pulse train is obtained from an adaptive code.

4. A speech decoding apparatus comprising:

linear prediction parameter decoding means;

excitation signal generating means;

a synthesis filter for synthesizing an output signal of said linear prediction parameter decoding means and an excitation signal output from said excitation signal generating means;

phase amplitude characteristic decoding means for decoding a coded short-term phase amplitude characteristic; and

a phase amplitude characteristic adding filter for adding the decoded short-term phase amplitude characteristic to said excitation signal.

5. A speech decoding apparatus according to claim 4, wherein said excitation signal generating means includes:

an adaptive codebook for outputting an adaptive vector;

a random codebook for outputting a random vector; and

excitation gain decoding means;

and uses a pulse train as said random vector.

6. A speech decoding apparatus according to claim 5, wherein a pulse interval of said pulse train is obtained from an adaptive code.

7. A speech coding and decoding method comprising a coding process and a decoding process:

said coding process including the steps of;

coding a linear prediction parameter by linear prediction analysis of an input speech signal;

quantizing and coding a short-term phase amplitude characteristic which is obtained by analyzing a linear prediction residual signal of an input speech signal;

selecting an excitation signal for generating optimal synthesized speech from an excitation codebook;

adding said short-term phase amplitude characteristic to said excitation signal; and

coding and transmitting said excitation signal; and

said decoding process including the steps of;

generating an excitation signal and a decoded linear prediction parameter signal on the basis of a received signal;

decoding the coded phase amplitude characteristic;

adding the decoded phase amplitude characteristic to said excitation signal; and

synthesizing said excitation signal and said decoded linear prediction parameter signal by a synthesis filter so as to generate an output speech signal.

8. A phase amplitude characteristic extracting apparatus for extracting a short-term phase amplitude characteristic of a signal, comprising:

a phase amplitude characteristic codebook which stores a plurality of short-term phase amplitude characteristics of a signal;

a phase amplitude characteristic removing filter for removing a phase amplitude characteristic;

residual signal generating means for generating a residual signal by removing a phase amplitude characteristic stored in said phase amplitude characteristic codebook from an input signal by said phase amplitude characteristic removing filter;

pulse approximated signal generating means for generating a pulse signal representation signal by reducing said residual signal to a small number of pulses;

trial signal generating means for generating a trial signal by adding each phase amplitude characteristic removed by said phase amplitude characteristic removing filter to said pulse signal representation signal; and

selecting and outputting means for selecting a phase amplitude characteristic which minimizes a distortion between said trial signal and said input signal, from said phase amplitude characteristic codebook and outputting the selected phase amplitude characteristic.