CA2301995C

CA2301995C - High quality speech coder at low bit rates

Info

Publication number: CA2301995C
Application number: CA002301995A
Authority: CA
Inventors: Kazunori Ozawa
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 1996-08-26
Filing date: 1997-08-25
Publication date: 2005-10-18
Anticipated expiration: 2017-08-25
Also published as: CA2301994A1; CA2301994C; CA2301995A1

Abstract

In a speech coder, a spectral parameter computer obtaining a plurality of spectral parameters from an input speech signal and quantizes the obtained spectral parameters. Even at low bit rates, the speech coder requires relatively less computational effort and experiences less sound quality deterioration.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude pulses, obtaining a sample position corresponding to a pulse position meeting a predetermined condition with respect to the computed pitch prediction signal, setting a pulse position retrieval range on the basis of a position obtained by shifting the obtained sample position by a predetermined number of samples, extracting the polarity of a cross-correlation calculated between input speech signal and impulse response obtained from said spectral parameter computer, for each position candidate in the retrieval range, retrieving a best position in the pulse position retrieval range thus set, and outputting data of the retrieved best position.

2. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude pulses, obtaining a sample position meeting a predetermined condition with respect to the pitch prediction signal in a time interval equal to the pitch period from the forefront of a frame, setting a pulse position retrieval range for retrieving a pulse position on the basis of a position obtained by shifting the obtained sample position by a predetermined number of samples, extracting the polarity of a cross-correlation calculated between input speech signal and impulse response obtained from said spectral parameter computer, for each position candidate in the retrieval range, retrieving a best position in the pulse position retrieval range thus set, and outputting data of the retrieved best position.

3. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude pulses, obtaining a sample position corresponding to a pulse position meeting a predetermined condition with respect to the computed pitch prediction signal in a time interval equal to the pitch period from the forefront of a frame, setting pulse position candidates through shifting the obtained sample position by the pitch period on the basis of the position shifted by predetermined numbers of samples from the sample position, extracting the polarity of a cross-correlation calculated between input speech signal and impulse response obtained from said spectral parameter computer, for each position candidate in the retrieval range, retrieving the position candidates for a best position, and outputting data of the retrieved best position.

4. The speech coder according to one of claims 1, 2 and 3, wherein the excitation quantizer includes a codebook for jointly quantizing the amplitudes or polarities of a plurality of pulses.

5. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude pulses, obtaining a sample position meeting a predetermined condition with respect to the computed pitch prediction signal, setting a plurality of pulse position retrieval ranges on the basis of positions obtained by shifting the obtained sample position by corresponding shift extents, extracting the polarity of a cross-correlation calculated between input speech signal and impulse response obtained from said spectral parameter computer, for each position candidate in the retrieval range, making retrieval of the pulse position retrieval ranges to select a best combination of a shift extent and a pulse position, and outputting data of the selected best combination.

6. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude pulses, obtaining a sample pulse position meeting a predetermined condition with respect to the computed pitch prediction signal in a time interval equal to the pitch period from the forefront of a frame, setting a plurality of pulse position retrieval ranges on the basis of positions obtained by shifting the obtained sample position by corresponding shift extents, extracting the polarity of a cross-correlation calculated between input speech signal and impulse response obtained from said spectral parameter computer, for each position candidate in the retrieval range, making retrieval of the pulse position retrieval ranges to select a best combination of a shift extent and a pulse position, and outputting data of the selected best combination.

7. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude pulses, obtaining a sample pulse position meeting a predetermined condition with respect to the computed pitch prediction signal in a time interval equal to the pitch period from the forefront of a frame, setting pulse position candidates through shifting the obtained sample position by the pitch period on the basis of the position shifted by predetermined numbers of samples from the sample position, extracting the polarity of a cross-correlation calculated between input speech signal and impulse response obtained from said spectral parameter computer, for each position candidate in the retrieval range, retrieving the position candidates for a best position, and outputting data of the retrieved best position.

8. The speech coder according to one of claims 5, 6 and 7, wherein the excitation quantizer includes a codebook for jointly quantizing the amplitudes or polarities of a plurality of pulses.

9. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, a mode judging means for extracting a characteristic amount from the input speech signal, judging a plurality of modes from the extracted feature quantity, and outputting mode data, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and making pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude signals, obtaining a sample position meeting a predetermined condition with respect to the pitch prediction signal when the mode data represents a predetermined mode, setting a pulse position retrieval range on the basis of the obtained sample position, extracting the polarity of a cross-correlation calculated between input speech signal and impulse response obtained from said spectral parameter computer, for each position candidate in the retrieval range, retrieving a best position in the pulse position retrieval range, and outputting data of the retrieved best position.

10. The speech coder according to claim 9, wherein the feature quantity is an average pitch prediction gain.

11. The speech coder according to claim 9, wherein the mode judging means judges the modes on the basis of comparison of the average pitch prediction gain with a plurality of threshold values.

12. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for obtaining a position meeting a predetermined condition with respect to the pitch prediction signal computed in the adaptive codebook means, setting a plurality of pulse position retrieval ranges for respective pulses constituting an excitation signal, extracting the polarity of a cross-correlation calculated between input speech signal and impulse response obtained from said spectral parameter computer, for each position candidate in the retrieval range, and retrieving the best positions of the pulses in the pulse position retrieval ranges.