Recursive pitch predictor employing an adaptively determined search window

• US 5,812,967 A
• Filed: 09/30/1996
• Issued: 09/22/1998
• Est. Priority Date: 09/30/1996
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Wu, Hsi-Jung, Chu, Ke-Chiang, Ponceleon, Dulce, Manduchi, Roberto
• Primary Examiner(s): Hudspeth, David R.
• Assistant Examiner(s): Wieland, Susan
• Application Number:
  US08/724,169
• Time in Patent Office: 722 Days
• Field of Search: 704/207, 704/2.17, 704/218, 704/219, 704/208, 704/237
• 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 2019/0011 Long term prediction filters, i.e. pitch estimation

Abstract

A method for improved recursive pitch prediction includes providing a search window for pitch estimates based upon a previously computed pitch, computing pitch estimates for the search window, and determining an optimal pitch from the pitch estimates within the search window for a first predetermined number of frames. The method further includes expanding the search window to a full pitch window after the first predetermined number of frames, and calculating pitch estimates for the full pitch window for a second predetermined number of frames.

A system for improved recursive pitch prediction includes a speech generator of speech signals, and a central processing unit coupled to the speech generator. The central processing unit further is capable of coordinating pitch estimation of the speech signals, including providing a search window for pitch estimates based upon a previously computed pitch, calculating pitch estimates for the search window, and determining an optimal pitch from the pitch estimates within the search window for a first predetermined number of frames.

Claims

1. A method for improved recursive pitch prediction in digital speech signal processing, the method comprising the steps of:

a) utilizing a search window that falls within a full pitch window for pitch estimates based upon a location of a previously computed pitch within the search window;

b) determining pitch estimates for the search window; and

c) determining an optimal pitch from the pitch estimates within the search window for a first predetermined number of frames, wherein inter-frame correlation of pitch in speech signals is better estimated.

2. The method of claim 1 further comprising expanding the search window to the full pitch window after the first predetermined number of frames.

3. The method of claim 2 further comprising the steps of:

d) determining estimates for the full pitch window; and

e) determining an optimal pitch estimate within the full pitch window for a second predetermined number of frames.

4. The method of claim 3 further comprising repeating steps a-c after the second predetermined number of frames.

5. The method of claim 1 wherein step (a) further comprises selecting a first limit of the search window at a maximum value between a previous pitch index value less a chosen displacement and a lower end of the full pitch window.

6. The method of claim 5 wherein step (a) further comprises selecting a second limit of the search window at a minimum value between the previous pitch index value plus the chosen displacement and an upper end of the full pitch window.

7. The method of claim 6 wherein the chosen displacement is approximately equal to one-third of the full pitch window length.

8. A system for improved recursive pitch prediction in digital speech signal processing comprising:

means for generating digital speech signals; and

a central processing unit, the central processing unit coupled to the speech generator and capable of coordinating pitch estimation of the speech signals, the pitch estimation comprising providing a search window within a full pitch window for pitch estimates based upon a location of a previously computed pitch within the search window, calculating pitch estimates for the search window, and determining an optimal pitch from the pitch estimates within the search window for a first predetermined number of frames.

9. The system of claim 8 wherein the pitch estimation further comprises expanding the search window to the full pitch window after the first predetermined number of frames.

10. The system of claim 9 wherein the pitch estimation further comprises computing pitch estimates for the full pitch window for a second predetermined number of frames.

11. The system of claim 8 wherein the pitch estimation further comprises selecting a first limit of the search window at a maximum value between a previous pitch index value less a chosen displacement and a lower end of the full pitch window.

12. The system of claim 11 wherein the pitch estimation further comprises selecting a second limit of the search window at a minimum value between the previous pitch index value plus the chosen displacement and an upper end of the full pitch window.

13. The system of claim 12 wherein the chosen displacement is approximately equal to one-third of the full pitch window length.

14. A system for improved recursive pitch estimation comprising:

speech signal generation means for generating speech signals; and

speech processing means for processing the generated speech signals to estimate a pitch of the speech signals by utilizing an adaptively determined search window, the adaptively determined search window comprising a smaller window within an exhaustive search window, providing pitch estimates for the adaptively determined search window, and determining an optimal pitch from the pitch estimates within the adaptively determined search window.

15. The system of claim 14 wherein the adaptively determined search window results from reducing the exhaustive search window based upon a pitch estimate computed for a previous frame.

16. The system of claim 15 wherein the speech processing means further selects a first limit of the search window at a maximum value between a previous pitch index value less a chosen displacement and a lower end of the exhaustive search window.

17. The system of claim 16 wherein the speech processing means further selects a second limit of the search window at a minimum value between the previous pitch index value plus the chosen displacement and an upper end of the exhaustive search window.

18. The system of claim 17 wherein the chosen displacement is approximately equal to one-third of the exhaustive search window length.

19. A computer readable medium containing program instructions for improved recursive pitch prediction in digital speech signal processing, the program instructions comprising:

a) utilizing a search window that falls within a full pitch window for pitch estimates based upon a location of a previously computed pitch within the search window;

b) determining pitch estimates for the search window; and

c) determining an optimal pitch from the pitch estimates within the search window for a first predetermined number of frames, wherein inter-frame correlation of pitch in speech signals is better estimated.