Method and system for speech encoding involving analyzing search range for current period according to length of preceding pitch period

• US 6,470,310 B1
• Filed: 09/28/1999
• Issued: 10/22/2002
• Est. Priority Date: 10/08/1998
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Oshikiri, Masahiro, Miseki, Kimio
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): NOLAN, DANIEL A
• Application Number:
  US09/407,060
• Time in Patent Office: 1,120 Days
• Field of Search: 704/220, 704/223, 704/222, 704/219, 704/233, 704/226, 704/207
• US Class Current: 704/207
• 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 25/90 Pitch determination of speech signals

Abstract

Processing for producing encoded output representing information about a pitch period of an input speech signal is performed. The pitch period of a previously entered speech signal is stored in a buffer. A search range-determining portion determines a range in which a current pitch period is analyzed, according to the pitch period of the previously entered speech signal. A presently entered speech signal is applied from a speech input terminal. A pitch analysis portion makes a pitch analysis of candidates for the pitch period contained in the determined search range. Information about the pitch period is delivered from an output terminal and stored in the buffer for subsequent processing. The pitch period of the speech signal can be calculated with a small amount of calculation and represented with a small amount of information.

Claims

1. A speech encoding method for encoding an input speech signal with the pitch period of the input speech signal, said method comprising:

dividing the input speech signal into a plurality of frames of a predetermined length and dividing each frame of the input speech signal into a plurality of subframes;

determining a search range searched to find the pitch period of a present subframe to be encoded, according to the length of the pitch period found in a previous subframe prior to the present subframe;

finding the pitch period of the present subframe from the search range; and

encoding the pitch period of the present subframe;

wherein;

when the pitch period of the present subframe is found, the search range is searched to find a plurality of candidates for the pitch period of the present subframe;

the candidates that are closer to the pitch period found in the previous subframe are spaced closely to each other; and

the candidates that are widely different from the pitch period found in the previous subframe are spaced widely from each other.

2. The speech encoding method of claim 1, wherein the search range is enlarged with increasing the length of the pitch period found in the previous subframe and narrowed with reducing the length of the pitch period found in the previous subframe.

3. The speech encoding method of claim 1, further comprising the steps of:

finding an amount of deviation of the pitch period of the present subframe from the pitch period of the previous subframe; and

encoding the amount of deviation as information about the pitch period of the present subframe.

4. A speech encoding method for encoding an input speech signal with the pitch period of the input speech signal, said method comprising:

dividing the input speech signal into a plurality of frames of a predetermined length and dividing each frame of the speech signal into a plurality of subframes;

determining a search range searched to find the pitch period of a present subframe, according to the length of the pitch period found in a previous subframe prior to the present subframe;

taking an adaptive vector from an adaptive codebook according to the pitch period of the present subframe;

passing the taken adaptive vector through a synthesis filter;

searching the adaptive vector that minimizes a difference between an output signal from the synthesis filter and a target vector; and

encoding the found adaptive vector;

wherein;

when the pitch period of the present subframe is found, the search range is searched to find a plurality of candidates for the pitch period of the present subframe;

the candidates that are closer to the pitch period found in the previous subframe are spaced closely to each other; and

the candidates that are widely different from the pitch period found in the previous subframe are spaced widely from each other.

5. The speech encoding method of claim 4, wherein:

the search range is enlarged with increasing length of the pitch period found in the previous subframe; and

the search range is narrowed with reducing length of the pitch period found in the previous subframe.

6. The speech encoding method of claim 4, further comprising:

finding an amount of deviation of the pitch period of the present subframe from the pitch period of the previous subframe; and

encoding the found amount of deviation as information about the pitch period of the present subframe.

7. A speech encoding system encoding an input speech signal in accordance with a pitch period of the input speech signal, said speech encoding system comprising:

a) a frame-and-subframe forming portion for dividing the input speech signal into a plurality of frames of a predetermined length and dividing each frame of the speech signal into a plurality of subframes; and

b) a search range-determining portion for determining a search range searched to find the pitch period of a present subframe to be encoded, according to the length of the pitch period of a previous subframe;

wherein a pitch-calculating portion arranges a plurality of candidates for the pitch period within the search range in such a way that;

1) the candidates that are closer to the pitch period found in the previous subframe are spaced closely to each other, and

2) the candidates that are widely different from the pitch period found in the previous subframe are spaced widely from each other.

8. The speech encoding system of claim 7, wherein the search range-determining portion determines the search range for an adaptive vector taken from an adaptive codebook about the present subframe.

9. The speech encoding system of claim 8, wherein:

the pitch period-calculating portion searches the adaptive vector that minimizes a difference between a filter output signal and a target vector, and

the filter output signal is obtained by passing the adaptive vector taken from the adaptive codebook through a synthesis filter.

10. The speech encoding system of claim 9, wherein the pitch period-calculating portion encodes the adaptive vector.

11. The speech encoding system of claim 7, wherein the search range-determining portion sets the search range wider with increasing the length of the pitch period found in the previous subframe and sets the search range narrower with reducing the length of the found pitch period found in the previous subframe.

12. The speech encoding system of claim 7, wherein the pitch period-calculating portion finds an amount of deviation of the pitch period of the present subframe from the pitch period of the previous subframe and encodes the amount of deviation as information about the pitch period of the present subframe.