Code conversion method, apparatus, program, and storage medium

• US 7,630,884 B2
• Filed: 11/12/2002
• Issued: 12/08/2009
• Est. Priority Date: 11/13/2001
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Murashima, Atsushi
• Primary Examiner(s): Lerner; Martin
• Application Number:
  US10/495,273
• Publication Number:
  US 20050010400A1
• Time in Patent Office: 2,583 Days
• Field of Search: 704/201, 704/219, 704/220, 704/221, 704/223, 704/225, 704/203, 704/207, 370/466
• US Class Current: 704/219
• CPC Class Codes: G10L 19/08 Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
• CPC Class Codes: G10L 19/173 Transcoding, i.e. converting between two coded representations avoiding cascaded coding-decoding
• CPC Class Codes: G10L 2019/0001 Codebooks
• CPC Class Codes: G10L 2019/0011 Long term prediction filters, i.e. pitch estimation

Abstract

The object of this invention is converting a code that has been obtained by encoding speech by one particular system is converted to code that can be decoded by another system with high speech quality, and moreover, with a low computational load in transmitting speech signal between different systems. This invention comprising an adaptive codebook (ACB) delay search range control circuit (1250 in FIG. 7) for calculating a search range control value from first adaptive codebook delay that is stored and held and said second adaptive codebook delay that is stored and held, and an adaptive codebook encoding circuit (1220 in FIG. 7) for calculating autocorrelation using speech signal from ACB delay including excitation signal and delay that is within a range stipulated by said search range control value, and selects the maximum autocorrelation as second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

Claims

1. A code conversion method for converting a first code string to a second code string, the method comprising steps of:

obtaining a first linear prediction coefficient and excitation signal information from said first code string and generating an excitation signal from said excitation signal information;

outputting said excitation signal or a speech signal that is generated from said excitation signal, and a first adaptive codebook delay that is contained in said excitation signal information, to an adaptive codebook generation circuit;

selecting, via said adaptive codebook generation circuit, a second adaptive codebook delay based on said excitation signal or said speech signal that is generated from said excitation signal, and said first adaptive codebook delay; and

supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

2. A code conversion method for converting a first code string to a second code string, the method comprising steps of:

obtaining a first linear prediction coefficient and excitation signal information from said first code string, and generating an excitation signal from said excitation signal information;

storing and holding a second adaptive codebook delay previously selected, that corresponds to code of an adaptive codebook delay in said second code string;

outputting said second adaptive codebook delay stored and held, and said excitation signal or a speech signal that is generated from said excitation signal and said first linear prediction coefficient, to an adaptive codebook generation circuit;

selecting a new second adaptive codebook delay, via said adaptive codebook generation circuit, based on said second adaptive codebook delay stored and held, and said excitation signal or said speech signal; and

supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

3. A code conversion device for receiving a first code string as input, converting to a second code string, and supplying said second code string as output, the device comprising:

a speech decoding circuit for obtaining a first linear prediction coefficient and excitation signal information from said first code string and driving a filter having said first linear prediction coefficient by means of an excitation signal that is obtained from said excitation signal information to generate a speech signal; and

an adaptive codebook code generation circuit for receiving said speech signal and a first adaptive codebook delay that is contained in said excitation signal, and using said speech signal and said first adaptive codebook delay to select a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

4. A computer readable medium storing a program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute processes of:

obtaining a first linear prediction coefficient and excitation signal information from said first code string and generating an excitation signal from said excitation signal information;

outputting said excitation signal or a speech signal that is generated from said excitation signal, and a first adaptive codebook delay that is contained in said excitation signal information, to an adaptive codebook generation circuit;

selecting, via said adaptive codebook generation circuit, a second adaptive codebook delay based on said excitation signal or said speech signal that is generated from said excitation signal, and said first adaptive codebook delay; and

supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

5. A computer readable medium storing a program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute processes of:

obtaining a first linear prediction coefficient and excitation signal information from said first code string, and generating an excitation signal from said excitation signal information;

storing and holding a second adaptive codebook delay previously selected, that corresponds to code of an adaptive codebook delay in said second code string;

outputting said second adaptive codebook delay stored and held, and said excitation signal or a speech signal that is generated from said excitation signal and said first linear prediction coefficient, to an adaptive codebook generation circuit;

selecting a new second adaptive codebook delay, via said adaptive codebook generation circuit, based on said second adaptive codebook delay stored and held, and said excitation signal or said speech signal; and

supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

6. A code conversion device for converting a first code string to a second code string, said code conversion device comprising:

a speech decoding circuit for obtaining a first linear prediction coefficient and excitation signal information from said first code string, and generating an excitation signal from said excitation signal information;

a second adaptive codebook delay storage circuit for, storing and holding a second adaptive codebook delay previously selected, that corresponds to code of an adaptive codebook delay in said second code string;

a adaptive codebook generation circuit for receiving said second adaptive codebook delay stored and held, and said excitation signal or a speech signal that is generated from said excitation signal and said first linear prediction coefficient and for selecting a new second adaptive codebook delay based on said second adaptive codebook delay stored and held, and said excitation signal or said speech signal; and

an adaptive codebook encoding circuit for supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.