Celp speech coding and decoding system for creating comfort noise dependent on the spectral envelope of the speech signal

• US 6,240,383 B1
• Filed: 07/27/1998
• Issued: 05/29/2001
• Est. Priority Date: 07/25/1997
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Tanaka, Seiko
• Primary Examiner(s): Korzuch, William R.
• Assistant Examiner(s): Smits, Talivaldis Ivars
• Application Number:
  US09/122,768
• Time in Patent Office: 1,037 Days
• Field of Search: 704/219, 704/233
• US Class Current: 704/219
• CPC Class Codes: G10L 19/012 Comfort noise or silence coding
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients

Abstract

A speech coding and decoding system consisting of a speech coding system and a speech decoding system, the speech coding system comprises a low pass filter using an LPC parameter, and an efficient coding processing unit for generating a coded speech signal by referring to a code book for a speech signal when coding a speech and generating a noise signal by referring to the code book for the signal filtered by the low pass filter when coding the information other than a speech, the speech decoding system comprises an efficient decoding processing unit for decoding the coded signal supplied from the speech coding system so to reproduce a speech signal, and a high pass filter using the LPC parameter for filtering a speech signal of an unvoiced sound area generated by the efficient decoding processing unit.

Claims

1. A speech coding and decoding method in a speech coding and decoding system that includes a speech coding system for coding a speech signal and transmitting the same and a speech decoding system receiving the coded signal transmitted from the speech coding system for decoding the same to supply speech, the method comprising:

in the speech coding system,

discriminating between a speech interval and a no-speech interval in an input sound signal,

in case of a speech interval in the judgement result,

generating a coded speech signal by referring to a code book created based on speech characteristics at the time of a speech sound as for a speech signal to be coded,

in case of a no-speech interval in the judgement result,

filtering the information other than speech of an input sound signal, through a filter using LPC parameters calculated from the input speech signal,

generating a noise signal by referring to the code book for the coded signal filtered, and

supplying the decoded speech signal or the noise signal while switching the decoded speech signal and the noise signal according to the judgement result, wherein,

in the speech decoding system,

discriminating between a speech interval and a no-speech interval upon receipt of a code signal supplied from a switch control means of the speech coding system,

decoding the input coded signal to generate a speech signal, and

in case of a speech interval in the judgement result,

filtering the generated speech signal, through a filter using LPC parameters calculated from the input coded signal.

2. A speech coding and decoding method as claimed in claim 1, wherein

said filtering step in the speech coding system comprises:

temporarily storing the LPC parameters for a sound at the time just before switching from a speech interval to a no-speech interval, according to the judgement in said speech/no-speech sound judging step, and

filtering the information other than speech of the input sound signal, by use of the stored LPC parameters as a filter coefficient.

3. A speech coding and decoding method as claimed in claim 1, wherein

said filtering step in the speech coding system comprises:

temporarily storing the LPC parameters calculated from the input coded signal in a speech interval, according to the judgement in said speech/no-speech sound judging step, and

filtering the decoded speech signal, by use of the stored LPC parameters as a filter coefficient.

4. A speech coding and decoding method as claimed in claim 1, wherein

said filtering step in the speech coding system comprises:

temporarily storing the LPC parameters for a sound at the time just before switching from a speech interval to a no-speech interval, according to the judgement in said speech/no-speech sound judging step, and

filtering the information other than speech of the input sound signal, by use of the stored LPC parameters as a filter coefficient, wherein

said filtering step in the speech decoding system comprises;

temporarily storing the LPC parameters calculated from the input coded signal in a speech interval, according to the judgement in said speech/no-speech sound judging step, and

filtering the decoded speech signal, by use of the stored LPC parameters as a filter coefficient.

7. A speech coding and decoding system as set forth in claim 1, wherein said first filtering means of the speech coding system comprises

a low pass filter for filtering the information other than speech of the input sound signal.

13. A speech coding and decoding system as set forth in claim 1, wherein

said speech coding system further comprises:

an LPC analyzing means for calculating LPC parameters for the input sound signal by use of a linear prediction analysis method in a speech interval, according to the judgment by said first speech/no-speech sound judging means,

a unique word generating means for supplying a unique word control signal for discriminating between a speech interval and a no-speech interval in a coded signal supplied from said coding processing means, wherein

said switch control means supplies a coded speech signal generated by said coding processing means as well as a unique word control signal indicating a speech interval, which is supplied from said unique word generating means, during a speech interval, and supplies a noise signal generated by said coding processing means as well as a unique word control signal indicating a no-speech interval, which is supplied from said unique word generating means, during a no-speech interval, according to the judgement by said first speech/no-speech sound judging means, and

said first filtering means comprises;

a low pass filter for filtering the information other than a speech of the input sound signal, and

said speech decoding system comprises;

a second speech/no-speech sound judging means receiving a coded signal supplied from a switch control means of the speech coding system for discriminating between a speech interval and a no-speech interval, based on the unique word control signal included in the input coded signal, and

an LPC decoding means for calculating LPC parameters based on the input coded signal for a speech interval, according to the judgement by said second speech/no-speech sound judging means, and

said second filtering means comprises;

an LPC storing means for temporarily storing the LPC parameters calculated by said LPC decoding means, and

a high pass filter for filtering the speech signal decoded by said decoding processing means, by use of the LPC parameters stored in said LPC storing means as a filter coefficient.

5. A speech coding and decoding system that includes a speech coding system for coding a speech signal and transmitting the same and a speech decoding system receiving the coded signal transmitted from the speech coding system for decoding the same to supply speech, wherein

said speech coding system comprising:

a first speech/no-speech sound judging means for discriminating between a speech interval and a no-speech interval in an input sound signal;

an LPC storing means for temporarily storing LPC parameters for a speech sound at a time just before switching from a speech interval to a no-speech interval, according to the judgement by said first speech/no-speech sound judging means;

a first filtering means for filtering the information other than speech of the input speech signal, by use of the LPC parameters stored in said LPC storing means as a filter coefficient;

a coding processing means for generating a coded speech signal by referring to a code book created based on speech characteristics at the time of a speech sound when coding speech, and generating a noise signal by referring to the code book for the coded signal filtered by said first filtering means when coding the information other than speech; and

a switch control means for supplying a coded speech signal generated by said coding processing means, during a speech interval, and supplying a noise signal generated by said coding processing means, during a no-speech interval, according to the judgement by said first speech/no-speech sound judging means; and

said speech decoding system comprising;

a decoding processing means receiving the coded signal supplied from said switch control means of the speech coding system for decoding the same to generate a speech signal; and

a second filtering means for filtering the speech signal generated by said decoding processing means, through a filter using the LPC parameters calculated from the input coded signal for a no-speech interval of the input coded signal.

6. A speech coding and decoding system as set forth in claim 5, wherein

said speech coding system further comprises,

an LPC analyzing means for calculating LPC parameters for the input sound signal by use of a linear prediction analysis method in a speech interval, according to the judgement by said first speech/no-speech sound judging means.

8. A speech coding and decoding system as set forth in claim 5, wherein

said speech coding system further comprises:

an LPC analyzing means for calculating LPC parameters for the input sound signal by use of a linear prediction analysis method in a speech interval, according to the judgement by said first speech/no-speech sound judging means, and

said first filtering means comprises;

a low pass filter for filtering the information other than speech of the input sound signal.

9. A speech coding and decoding system as set forth in claim 5, wherein

said speech decoding system comprises:

a second speech/no-speech sound judging means receiving the coded signal supplied from a switch control means of the speech coding system for discriminating between a speech interval and a no-speech interval, and

an LPC decoding means for calculating LPC parameters based on the input coded signal in a speech interval, according to the judgement by said second speech/no-speech sound judging means.

10. A speech coding and decoding system as set forth in claim 5, wherein

said speech decoding system comprises:

a second speech/no-speech sound judging means receiving the coded signal supplied from a switch control means of the speech coding system for discriminating between a speech interval and a no-speech interval, and

an LPC decoding means for calculating LPC parameters based on the input coded signal in a speech interval, according to the judgement by said second speech/no-speech sound judging means, and

said second filtering means comprises;

an LPC storing means for temporarily storing the LPC parameters calculated by said LPC decoding means, and

a high pass filter for filtering the speech signal decoded by said decoding processing means by use of the LPC parameters stored in said LPC storing means as a filter coefficient.

11. A speech coding and decoding system as set forth in claim 5, wherein said speech coding system further comprises:

an LPC analyzing means for calculating LPC parameters for the input sound signal by use of a linear prediction analysis method in a speech interval, according to the judgement by said first speech/no-speech sound judging means, and

said first filtering means comprises;

a low pass filter for filtering the information other than speech of the input sound signal, and

said speech decoding system comprises;

a second speech/no-speech sound judging means receiving the coded signal supplied from a switch control means of the speech coding system for discriminating between a speech interval and a no-speech interval, and

an LPC decoding means for calculating LPC parameters based on the input coded signal for a speech interval, according to the judgement by said second speech/no-speech sound judging means, and

said second filtering means comprises;

an LPC storing means for temporarily storing the LPC parameters calculated by said LPC decoding means, and

a high pass filter for filtering the speech signal decoded by said decoding processing means, by use of the LPC parameters stored in said LPC storing means as a filter coefficient.

12. A speech coding and decoding system as set forth in claim 5, wherein

said speech coding system further comprises:

a unique word generating means for supplying a unique word control signal for discriminating between a speech interval and a no-speech interval in a coded signal supplied from said coding processing means, wherein

said switch control means supplies a coded speech signal generated by said coding processing means as well as a unique word control signal indicating a speech interval, which is supplied from said unique word generating means, during a speech interval, and supplies a noise signal generated by said coding processing means as well as a unique word control signal indicating a no-speech interval, which is supplied from said unique word generating means, during a no-speech interval, according to the judgement by said first speech/no-speech sound judging means, while

said speech decoding system further comprises;

a second speech/no-speech sound judging means receiving a coded signal supplied from a switch control means of the speech coding system for discriminating a speech interval and a no-speech interval based on the unique word control signal included in the input coded signal.