Speech coder for high quality at low bit rates

• US 6,751,585 B2
• Filed: 09/07/2001
• Issued: 06/15/2004
• Est. Priority Date: 11/27/1995
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Ozawa, Kazunori
• Primary Examiner(s): ABEBE, DANIEL DEMELASH
• Application Number:
  US09/948,481
• Publication Number:
  US 20020029140A1
• Time in Patent Office: 1,012 Days
• Field of Search: 704/200, 704/219, 704/220, 704/222, 704/223, 704/230, 704/258, 704/262, 704/264, 704/500
• US Class Current: 704/219
• CPC Class Codes: G10L 19/07 Line spectrum pair [LSP] vocoders
• CPC Class Codes: G10L 2019/0001 Codebooks

Abstract

A speech coder for high quality coding speech signals at low bit rates is disclosed. An excitation quantization unit 12 expresses an excitation signal in terms of a combination of a plurality of pulses. A codebook (i.e., an amplitude codebook 13) collectively quantizes either amplitude or position of pulses, and executes excitation signal quantization other parameter by making retrieval of the codebook.

Claims

1. A speech coder comprising:

a spectral parameter calculator that generates a quantized spectral parameter from an input speech signal;

an excitation quantizer that derives an excitation signal from the input speech signal using the spectral parameter and outputs the excitation signal in quantized form, the excitation signal comprising a plurality of non-zero pulses, each non-zero pulse being characterized by a pulse position parameter and a pulse amplitude parameter; and

a codebook that simultaneously quantizes one of the pulse position parameter and the pulse amplitude parameter of all of the non-zero pulses, the excitation quantizer being operative to quantize the non-zero pulses by computation using the one parameter obtained by retrieval of the codebook to determine the other of the pulse position parameter and the pulse amplitude parameter.

2. The speech coder according to claim 1, wherein the excitation quantizer has at least one specific pulse position at which a pulse is taken.

3. The speech coder according to claim 1, wherein the excitation quantizer preliminarily selects a plurality of codevectors from the codebook and executes the quantization by obtaining the other parameter by retrieval of the preliminarily selected codevectors.

4. The speech coder according to claim 1, wherein the codebook quantizes the amplitude parameter of the plurality of non-zero pulses.

5. The speech coder according to claim 1, further including a position memory that stores a plurality of predetermined pulse-position combinations;

and wherein the excitation quantizer is operative to derive the excitation signal using the codebook entries and the succession of pulse-position combinations stored in the position memory.

6. The speech coder according to claim 1, wherein the excitation quantizer is operative to perform a preliminary selection of entries from the codebook according to a predetermined algorithm, and to assign, in succession, to each of the preliminarily selected codebook entries, possible positions that may be assumed by each of the plurality of pulses.

7. The speech coder according to claim 1, further including a frame dividing circuit that divides the incoming speech signal into a succession of N-pulse frames, and wherein:

the spectral parameter is extracted and quantized on a frame-by-frame basis;

the excitation is in the form of an M-pulse codevector (M<

N) having only non-zero pulses, each of which pulses can assume a predetermined quantized amplitude and position;

the entries in the code book comprise permutations of quantized amplitude values which can be assumed by each of the M pulses, but no information as the position of each of the M pulses; and

the excitation quantizer is operative to assign, in succession, to each of the codebook entries, possible positions that may be assumed by each of the M pulses thereof, and to perform a computation to determine which position-amplitude combination results in a reconstructed speech signal which most closely approximates the input speech signal.

8. The speech coder according to claim 7, further including a position memory that stores a plurality of predetermined pulse-position combinations;

and wherein the excitation quantizer is operative to assign, in succession, to each of the codebook entries, the succession of pulse-position combinations stored in the position memory, and to perform a computation to determine which position-amplitude combination results in a reconstructed speech signal which most closely approximates the input speech signal.

9. The speech coder according to claim 7, wherein the excitation quantizer is operative to:

perform a preliminary selection of entries from the codebook according to a predetermined algorithm;

assign, in succession, to each of the preliminarily selected codebook entries, possible positions that may be assumed by each of the M pulses thereof; and

perform a computation to determine which position-amplitude combination results in a reconstructed speech signal which most closely approximates the input speech signal.

10. The speech coder according to claim 9, further including an adaptive codebook, and pitch prediction circuitry operative in conjunction with the adaptive codebook, and wherein the predetermined preliminary selection algorithm employs an output of the adaptive codebook and the spectral parameter.

11. A method of speech encoding comprising:

generating a quantized spectral parameter from a speech signal;

deriving an excitation signal from the speech signal, the excitation signal comprising a plurality of non-zero pulses, each non-zero pulse being characterized by a pulse position parameter and a pulse amplitude parameter; and

simultaneously quantizing one of the pulse position parameter and the pulse amplitude parameter of the plurality of non-zero pulses; and

determining the other of the pulse position parameter and the pulse amplitude parameter using the quantized parameter of the plurality of non-zero pulses.

12. The method of speech encoding according to claim 11, further comprising taking a pulse at at least one specific pulse position.

13. The method of speech encoding according to claim 11, further comprising selecting a plurality of codevectors from a code book, wherein the other of the pulse position parameter and the pulse amplitude parameter is determined using the selected plurality of codevectors.

14. The method of speech encoding according to claim 11, further comprising:

dividing the speech signal into a succession of N-pulse frames;

extracting and quantizing the spectral parameter on a frame-by-frame basis, the excitation signal being in the form of an M-pulse codevector (M<

N) having only non-zero pulses, each pulse of which can assume a predetermined quantized amplitude and position;

assigning, in succession, possible positions that may be assumed by each of the M pulses; and

performing a computation to determine which position-amplitude combination results in a reconstructed speech signal which most closely approximates the speech signal.

15. The method of speech encoding according to claim 14, further comprising performing a preliminary selection of codebook entries according to a predetermined algorithm.

16. The method of speech encoding according to claim 15, further comprising assigning, to each of the preliminarily selected codebook entries, possible positions that may be assumed by each of the plurality of pulses.

17. The method of speech encoding according to claim 11, wherein the amplitude parameter of the plurality of non-zero pulses is quantized.

18. The method of speech encoding according to claim 11, further comprising:

storing a plurality of predetermined pulse-position combinations; and

deriving the excitation signal using the stored plurality of pulse-position combinations.