Speech coding

• US 20050137858A1
• Filed: 12/19/2003
• Published: 06/23/2005
• Est. Priority Date: 12/19/2003
• Status: Active Grant

• Current Assignee: Nokia Corporation
• Original Assignee: Nokia Corporation
• Inventors: Ramo, Anssi, Heikkinen, Ari, Himanen, Sakari
• Granted Patent: US 7,523,032 B2
• Time in Patent Office: Days
• US Class Current: 704/205
• 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 19/16 Vocoder architecture
• CPC Class Codes: G10L 19/265 Pre-filtering, e.g. high frequency emphasis prior to encoding

Abstract

The invention relates to a method for use in parametric speech coding. In order to enable an improved parametric coding of speech signals, the method comprises a first step of pre-processing a to be encoded speech based signal such that a phase structure of the to be encoded speech based signal is approached to a phase structure which is obtained when the to be encoded speech based signal is parametrically encoded and decoded again. Only in a second step, a parametric encoding is applied to this pre-processed to be encoded speech based signal. The invention relates equally to a corresponding device, to a corresponding coding module, to a corresponding system and to a corresponding software program product.

Claims

1. A method for use in speech coding, said method comprising:

pre-processing a to be encoded speech based signal such that a phase structure of said to be encoded speech based signal is approached to a phase structure which would be obtained if said to be encoded speech based signal was encoded and decoded; and

applying an encoding to said pre-processed to be encoded speech based signal.

2. The method according to claim 1, wherein said speech coding is a parametric speech coding employing at least one parameter indicative of the phase of said to be encoded speech based signal.

3. The method according to claim 1, wherein said to be encoded speech based signal is pre-processed and encoded on a frame-by-frame basis.

4. The method according to claim 3, wherein said pre-processing comprises modifying a respective frame of said to be encoded speech based signal such that a phase contour of said pre-processed to be encoded speech based signal over said frame corresponds basically to a synthetic phase contour determined from pitch estimates for said to be encoded speech based signal.

5. The method according to claim 3, wherein pre-processing said to be encoded speech based signal comprises for a respective frame of said to be encoded speech signal:

estimating a pitch for said frame;

determining a synthetic phase contour over said frame based on said pitch estimate and a pitch estimate for a preceding frame;

locating pitch pulse positions in said determined synthetic phase contour;

locating pitch pulse positions in said frame of said to be encoded speech based signal; and

modifying said to be encoded speech based signal in said frame such that the positions of its pitch pulses are shifted to the positions of said pitch pulses of said synthetic phase contour.

6. The method according to claim 5, wherein said pitch pulses in said to be encoded signal are located by means of a signal energy contour.

7. The method according to claim 5, wherein said to be encoded speech signal is modified by means of time warping.

8. The method according to claim 5, wherein for those frames of said to be encoded speech signal in which no reliable pitch pulse position is found, a coding without pre-processing of said to be encoded signal is employed.

9. The method according to claim 1, wherein said to be encoded speech based signal is one of an original speech signal and a linear prediction residual of an original speech signal.

10. The method according to claim 1, wherein said pre-processing to be encoded speech based signal is encoded by one of an open-loop parametric coding and a closed-loop parametric coding.

11. A device for performing a speech coding, said device comprising:

a pre-processing portion adapted to pre-process a to be encoded speech based signal such that a phase structure of said to be encoded speech based signal is approached to a phase structure which would be obtained if said to be encoded speech based signal was encoded and decoded; and

a coding portion which is adapted to apply an encoding to a to be encoded speech based signal.

12. The device according to claim 11, wherein said coding portion applies a parametric speech coding to a to be encoded speech based signal employing at least one parameter indicative of the phase of said to be encoded speech based signal.

13. The device according to claim 11, wherein said pre-processing portion and said coding portion pre-process and encode a to be encoded speech based signal, respectively, on a frame-by-frame basis.

14. The device according to claim 13, wherein said pre-processing by said pre-processing portion comprises modifying a respective frame of a to be encoded speech based signal such that a phase contour of said pre-processed to be encoded speech based signal over said frame corresponds basically to a synthetic phase contour determined from pitch estimates for said to be encoded speech based signal.

15. The device according to claim 13, wherein said pre-processing by said pre-processing portion comprises for a respective frame of a to be encoded speech signal:

estimating a pitch for said frame;

determining a synthetic phase contour over said frame based on said pitch estimate and a pitch estimate for a preceding frame;

locating pitch pulse positions in said determined synthetic phase contour;

locating pitch pulse positions in said frame of said to be encoded speech based signal; and

modifying said to be encoded speech based signal in said frame such that the positions of its pitch pulses are shifted to the positions of said pitch pulses of said synthetic phase contour.

16. The device according to claim 11, wherein said device is one of a mobile terminal and a network element.

17. A coding module for performing a speech coding, said coding module comprising:

a pre-processing portion adapted to pre-process a to be encoded speech based signal such that a phase structure of said to be encoded speech based signal is approached to a phase structure which would be obtained if said to be encoded speech based signal was encoded and decoded; and

a coding portion which is adapted to apply an encoding to a to be encoded speech based signal.

18. The coding module according to claim 17, wherein said coding portion applies a parametric speech coding to a to be encoded speech based signal employing at least one parameter indicative of the phase of said to be encoded speech based signal.

19. The coding module according to claim 17, wherein said pre-processing portion and said coding portion pre-process and encode a to be encoded speech based signal, respectively, on a frame-by-frame basis.

20. The coding module according to claim 19, wherein said pre-processing by said pre-processing portion comprises modifying a respective frame of a to be encoded speech based signal such that a phase contour of said pre-processed to be encoded speech based signal over said frame corresponds basically to a synthetic phase contour determined from pitch estimates for said to be encoded speech based signal.

21. The coding module according to claim 19, wherein said pre-processing by said pre-processing portion comprises for a respective frame of a to be encoded speech signal:

estimating a pitch for said frame;

determining a synthetic phase contour over said frame based on said pitch estimate and a pitch estimate for a preceding frame;

locating pitch pulse positions in said determined synthetic phase contour;

locating pitch pulse positions in said frame of said to be encoded speech based signal; and

modifying said to be encoded speech based signal in said frame such that the positions of its pitch pulses are shifted to the positions of said pitch pulses of said synthetic phase contour.

22. A system comprising at least one device for performing a speech coding, said at least one device comprising:

a pre-processing portion adapted to pre-process a to be encoded speech based signal such that a phase structure of said to be encoded speech based signal is approached to a phase structure which would be obtained if said to be encoded speech based signal was encoded and decoded; and

a coding portion which is adapted to apply an encoding to a to be encoded speech based signal.

23. The system according to claim 22, wherein said coding portion of said at least one device applies a parametric speech coding to a to be encoded speech based signal employing at least one parameter indicative of the phase of said to be encoded speech based signal.

24. The system according to claim 22, wherein said pre-processing portion and said coding portion of said at least one device pre-process and encode a to be encoded speech based signal, respectively, on a frame-by-frame basis.

25. The system according to claim 24, wherein said pre-processing by said pre-processing portion of said at least one device comprises modifying a respective frame of a to be encoded speech based signal such that a phase contour of said pre-processed to be encoded speech based signal over said frame corresponds basically to a synthetic phase contour determined from pitch estimates for said to be encoded speech based signal.

26. The system according to claim 24, wherein said pre-processing by said pre-processing portion of said at least one device comprises for a respective frame of a to be encoded speech signal:

estimating a pitch for said frame;

determining a synthetic phase contour over said frame based on said pitch estimate and a pitch estimate for a preceding frame;

locating pitch pulse positions in said determined synthetic phase contour;

locating pitch pulse positions in said frame of said to be encoded speech based signal; and

modifying said to be encoded speech based signal in said frame such that the positions of its pitch pulses are shifted to the positions of said pitch pulses of said synthetic phase contour.

27. The system according to claim 22, wherein said at least one device is at least one of a mobile terminal and a network element.

28. A software program product in which a software code for use in speech coding is stored, said software code realizing the following steps when running in a processing unit:

pre-processing a to be encoded speech based signal such that a phase structure of said to be encoded speech based signal is approached to a phase structure which would be obtained if said to be encoded speech based signal was encoded and decoded; and

applying an encoding to said pre-processed to be encoded speech based signal.

29. The software program product according to claim 28, wherein said speech coding is a parametric speech coding employing at least one parameter indicative of the phase of a to be encoded speech based signal.

30. The software program product according to claim 28, wherein said to be encoded speech based signal is pre-processed and encoded on a frame-by-frame basis.

31. The software program product according to claim 30, wherein said pre-processing comprises modifying a respective frame of said to be encoded speech based signal such that a phase contour of said pre-processed to be encoded speech based signal over said frame corresponds basically to a synthetic phase contour determined from pitch estimates for said to be encoded speech based signal.

32. The software program product according to claim 30, wherein pre-processing said to be encoded speech based signal comprises for a respective frame of said to be encoded speech signal:

estimating a pitch for said frame;

determining a synthetic phase contour over said frame based on said pitch estimate and a pitch estimate for a preceding frame;

locating pitch pulse positions in said determined synthetic phase contour;

locating pitch pulse positions in said frame of said to be encoded speech based signal; and

modifying said to be encoded speech based signal in said frame such that the positions of its pitch pulses are shifted to the positions of said pitch pulses of said synthetic phase contour.