Phase quantization method and apparatus

• US 6,292,777 B1
• Filed: 01/29/1999
• Issued: 09/18/2001
• Est. Priority Date: 02/06/1998
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Nishiguchi, Masayuki, Inoue, Akira
• Primary Examiner(s): Korzuch, William
• Assistant Examiner(s): Chawan, Vijay B
• Application Number:
  US09/239,515
• Time in Patent Office: 963 Days
• Field of Search: 704/207, 704/230, 704/219, 704/220, 704/223, 704/229, 704/205, 704/208, 704/221, 704/222
• US Class Current: 704/230
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders

Abstract

A phase quantization method and apparatus in which the phase information of the input signal such as at the time of the sinusoidal synthesis encoding can be quantized efficiently. The phase of the input signal derived from speech signals from an input terminal 11 is found by a phase detection unit 12 and scalar-quantized by a scalar quantizer 13. The spectral amplitude weighting k of each harmonics is calculated by a weighting calculation unit 18 based on the LPC coefficients from a terminal 17. Using the weighting k, a bit allocation calculation unit 19 calculates an optimum number of quantization bits of respective harmonics to send the calculated optimum number to the scalar quantizer 13.

Claims

1. A phase quantization apparatus comprising:

assignment bit number calculating means for calculating an optimum number of quantization bits assigned to respective harmonics of input speech signals; and

quantization means for quantizing a phase of the respective harmonics of signals derived from the input speech signals in accordance with the assigned number of bits calculated by the assignment bit number calculating means.

2. The phase quantization apparatus according to claim 1, wherein the signals derived from the input speech signals are speech signals.

3. The phase quantization apparatus according to claim 1, wherein the signals derived from the input speech signals are signal waveforms of short-term prediction residual signals of speech signals.

4. The phase quantization apparatus according to claim 1, wherein the assignment bit number calculating means calculates the optimum number of quantization bits assigned to the respective harmonics using short-term prediction residual signals of the input speech signals.

5. The phase quantization apparatus according to claim 1, further comprising:

phase prediction means for performing a quantization for each frame of a pre-set length on a time axis to predict the phase of the respective harmonics of a current frame of the signals derived from the input speech signals from the results of phase quantization of a previous frame; and

said quantization means quantizes a prediction error between the phase of the respective harmonics of the current frame and a predicted phase found by the phase prediction means depending on a number of assigned bits calculated by the assignment bit number calculating means.

6. The phase quantization apparatus according to claim 5, wherein the prediction error between the predicted error and the phase of the current frame is quantized only when the drift of a pitch frequency of the speech signals from the previous frame up to the current frame is within a pre-set range.

7. A phase quantization method comprising:

an assignment bit number calculating step of calculating an optimum number of quantization bits assigned to respective harmonics of input speech signals; and

a quantization step of quantizing a phase of the respective harmonics of signals derived from the input speech signals in accordance with the assigned number of bits calculated by the assignment bit number calculating step.

8. The phase quantization method according to claim 7, wherein the assignment bit number calculating step calculates the optimum number of quantization bits assigned to the respective harmonics using short-term prediction coefficients of the input speech signals.

9. The phase quantization method according to claim 7, further comprising:

a phase prediction step of performing a quantization for each frame of a pre-set length on a time axis to predict the phase of the respective harmonics of a current frame of signals derived from the input speech signals from the results of phase quantization of a previous frame; and

said quantization step quantizes a prediction error between the phase of the respective harmonics of the current frame and a predicted phase found by the phase prediction step depending on a number of assigned bits calculated by the assignment bit number calculating step when the drift of a pitch frequency of the speech signals from the previous frame to the current frame is in a pre-set range.

10. A phase quantization apparatus comprising:

assignment bit number calculating means for calculating an optimum number of quantization bits assigned to respective harmonics of input speech signals; and

quantization means for quantizing a difference between an approximated phase of respective harmonics components as found from an approximation line of unwrapped phase characteristics for a phase of the respective harmonics components of signals derived from the input speech signals and the phase of the respective harmonics components of the signals derived from the input speech signals depending on the optimum number of assigned bits calculated by the assignment bit number calculating means.

11. The phase quantization apparatus according to claim 10, wherein the signals derived from the input speech signals are speech signals.

12. The phase quantization apparatus according to claim 10, wherein the signals derived from the input speech signals are signal waveforms of short-term prediction residual signals of speech signals.

13. The phase quantization apparatus according to claim 10, wherein the assignment bit number calculating means calculates the optimum number of quantization bits assigned to the respective harmonics using short-term prediction residual signals of the input speech signals.

14. The phase quantization apparatus according to claim 10, wherein the approximation line is found by performing least square line approximation weighted by spectral amplitude of the input speech signals on the unwrapped phase characteristics.

15. The phase quantization apparatus according to claim 14, wherein an intercept of the approximation line is found by back-calculations from a phase of a harmonic component having a maximum weighting coefficient.

16. The phase quantization apparatus according to claim 14, wherein the approximate phase is found from a phase of the approximation line by a tilt and an intercept obtained on quantizing the tilt and the intercept of the approximation line.

17. The phase quantization apparatus according to claim 10 further comprising:

tilt prediction means for performing a quantization for each frame of a pre-set length on a time axis and for predicting a tilt of the approximation line of a current frame of the signals derived from the input speech signals from the results of quantization of the tilt of the approximation line of a previous frame and from a pitch lag of the current frame; and

said quantization means quantizes a predicted error of said tilt.

18. A phase quantization method comprising:

an assignment bit number calculating step of calculating an optimum number of quantization bits assigned to respective harmonics of input speech signals; and

a quantization step of quantizing a difference between an approximated phase of respective harmonics components as found from an approximation line of unwrapped phase characteristics for a phase of respective harmonics components of signals derived from the input speech signals and the phase of the respective harmonics components of the signals derived from the input speech signals depending on the optimum number of assigned bits calculated by the assignment bit number calculating step.

19. The phase quantization method according to claim 18, wherein the assignment bit number calculating step calculates the optimum number of assigned bits to the respective harmonics components using short-term prediction coefficients of the input speech signals.

20. The phase quantization method according to claim 18, wherein the approximation line is found by performing least square line approximation weighted by spectral amplitude of the input speech signals on the unwrapped phase characteristics.