Method and system for improving voice quality of a vocoder

• US 20060025990A1
• Filed: 07/28/2004
• Published: 02/02/2006
• Est. Priority Date: 07/28/2004
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Boillot, Marc A., Desai, Pratik V., Behboodian, Ali
• Granted Patent: US 7,117,147 B2
• Time in Patent Office: Days
• US Class Current: 704/207
• CPC Class Codes: G10L 19/09 Long term prediction, i.e. removing periodical redundancies, e.g. by using adaptive codebook or pitch predictor

Abstract

The invention concerns a method (300) and system (100) for improving voice quality of a vocoder (138, 158). The method includes the steps of monitoring (312) a pitch of a voice signal (400) at a transmitting unit (110); when the pitch of the voice signal reaches a predetermined threshold (840), shifting (326) the pitch of the voice signal to at least a portion of a predetermined range (810); transmitting (338) the pitch-shifted voice signal to a receiving unit (112); and at the receiving unit, reshifting (342) the pitch-shifted voice signal to a level that compensates the step of shifting the pitch of the voice signal at the transmitting unit.

Claims

1. A method for improving voice quality of a vocoder, comprising the steps of:

monitoring a pitch of a voice signal;

at a transmitting unit, when the pitch of the voice signal reaches a predetermined threshold, shifting the pitch of the voice signal to at least a portion of a predetermined range;

transmitting the pitch-shifted voice signal to a receiving unit; and

at the receiving unit, reshifting the pitch-shifted voice signal to a level that compensates the step of shifting the pitch of the voice signal at the transmitting unit.

2. The method according to claim 1, wherein the voice signal is comprised of a plurality of time-based frames and wherein the monitoring the pitch step comprises the steps of:

estimating the pitch of the voice signal for at least a portion of the time-based frames of the voice signal; and

based on the estimating step, generating a pitch contour of the voice signal.

3. The method according to claim 2, wherein the voice signal is comprised of voiced and unvoiced portions and wherein the generating the pitch contour step comprises the step of interpolating the pitch contour for the unvoiced portions of the voice signal.

4. The method according to claim 1, further comprising the steps of:

in the transmitting unit, detecting speech on the voice signal; and

when detecting speech on the voice signal, determining whether the speech is comprised of voiced and unvoiced portions.

5. The method according to claim 1, wherein if no speech is detected on the voice signal, the method further comprises the step of inserting at least one silence frame into the voice signal.

6. The method according to claim 5, further comprising the step of converting at least one of the silence frames to pitch frames, wherein the pitch frames signal the receiving unit that the pitch-shifted voice signal was pitch shifted.

7. The method according to claim 6, wherein the pitch frames further signal the receiving unit of the magnitude that the pitch-shifted voice signal was shifted.

8. The method according to claim 5, further comprising the step of adding at least one pitch frame to the voice signal, wherein the pitch frames signal the receiving unit that the pitch-shifted voice signal was pitch shifted.

9. The method according to claim 8, wherein the pitch frames further signal the receiving unit of the magnitude that the pitch-shifted is to be reshifted.

10. The method according to claim 1, wherein the pitch of the voice signal is shifted by one of increasing and decreasing the pitch of the voice signal.

11. The method according to claim 1, further comprising the steps of:

encoding the pitch-shifted voice signal at the transmitting unit; and

decoding the pitch-shifted voice signal at the receiving unit.

12. The method according to claim 1, further comprising the step of detecting at least one of a voiced and an unvoiced condition on the voice signal.

13. The method according to claim 1, wherein the predetermined threshold is a compression window and wherein the predetermined range is between the maximum encoding pitch level and the minimum encoding pitch level of the vocoder.

14. The method according to claim 1, wherein the pitch of the voice signal is shifted from a first level to the portion of the predetermined range and wherein the pitch-shifted voice signal is reshifted at the receiving unit to a second level that is at least substantially equal to the first level.

15. A method for improving voice quality of a vocoder, comprising the steps of:

generating a pitch contour of a voice signal;

monitoring the pitch contour of the voice signal;

at a transmitting unit, when the pitch contour reaches a predetermined threshold, shifting the pitch of the voice signal from a first level to at least a portion of a predetermined range;

transmitting the pitch-shifted voice signal to a receiving unit; and

at the receiving unit, reshifting the pitch-shifted voice signal to a second level that is at least substantially equal to the first level.

16. A system for improving voice quality of a vocoder, comprising:

a pitch analysis section, wherein the pitch analysis section monitors a pitch of a voice signal;

a pitch shifter coupled to the pitch analysis section, wherein when the pitch analysis section determines that the pitch of the voice signal has reached a predetermined threshold, the pitch shifter shifts the pitch of the voice signal to at least a portion of a predetermined range;

an encoding section coupled to the pitch shifter, wherein the encoding block encodes the voice signal and provides pitch-shifting information in the voice signal; and

a transmission section coupled to the encoding section, wherein the transmission section transmits the pitch-shifted voice signal to a receiving unit, wherein the receiving unit uses the pitch-shifting information to reshift the pitch-shifted voice signal to a level that compensates the pitch shifting performed by the pitch shifter.

17. The system according to claim 16, wherein the voice signal is comprised of a plurality of time-based frames and wherein the pitch analysis section comprises a pitch estimating block and a pitch contour block, wherein the pitch estimating block estimates the pitch of the voice signal for at least a portion of the time-based frames of the voice signal and the pitch contour block generates a pitch contour of the voice signal based on the pitch estimation.

18. The system according to claim 17, wherein the voice signal is comprised of voiced and unvoiced portions and wherein the pitch contour block interpolates the pitch contour for the unvoiced portions of the voice signal.

19. The system according to claim 16, wherein the pitch analysis section further comprises a speech activity detector and a voiced/unvoiced detector, wherein the speech activity detector detects speech on the voice signal and when the speech activity detector detects speech on the voice signal, the voiced/unvoiced detector determines whether the speech is comprised of voiced and unvoiced portions.

20. The system according to claim 16, wherein the encoding section comprises a silent frame block, wherein if no speech is detected on the voice signal, the silent frame block inserts at least one silence frame into the voice signal.

21. The system according to claim 20, wherein the silent frame block converts at least one of the silence frames to a pitch frame, wherein the pitch frames signal the receiving unit that the pitch-shifted voice signal was pitch shifted.

22. The system according to claim 21, wherein the pitch frames further signal the receiving unit of the magnitude that the pitch-shifted voice signal was shifted.

23. The system according to claim 20, wherein the silent frame block adds at least one pitch frame to the voice signal, wherein the pitch frames signal the receiving unit that the pitch-shifted voice signal was pitch shifted.

24. The system according to claim 23, wherein the pitch frames further signal the receiving unit of the magnitude that the pitch-shifted voice signal was shifted.

25. The system according to claim 16, wherein the pitch shifter shifts the pitch of the voice signal by one of increasing and decreasing the pitch of the voice signal.

26. The system according to claim 16, wherein the encoding section further comprises a vocoder, wherein the vocoder encodes the pitch-shifted voice signal and wherein the receiving unit comprises a vocoder for decoding the pitch-shifted voice signal.

27. The system according to claim 16, wherein the pitch analysis section further comprises a voiced/unvoiced detector, wherein the voiced/unvoiced detector detects at least one of a voiced and an unvoiced condition on the voice signal.

28. The system according to claim 16, wherein the encoding section comprises a vocoder, wherein the predetermined threshold is a compression window and wherein the predetermined range is between the maximum encoding pitch level and the minimum encoding pitch level of the vocoder.

29. The system according to claim 16, wherein the pitch shifter shifts the pitch of the voice signal from a first level to the portion of the predetermined range and wherein the receiving unit reshifts the pitch-shifted voice signal to a second level that is at least substantially equal to the first level.

30. A system for improving voice quality of a vocoder, comprising:

a pitch analysis section, wherein the pitch analysis section generates a pitch contour of a voice signal and monitors the pitch contour of the voice signal;

a pitch shifter coupled to the pitch analysis section, wherein when the pitch contour reaches a predetermined threshold, the pitch shifter shifts the pitch of the voice signal from a first level to at least a portion of a predetermined range;

an encoding section coupled to the pitch shifter, wherein the encoding block encodes the voice signal and provides pitch-shifting information in the voice signal; and

a transmission section coupled to the encoding section, wherein the transmission section transmits the pitch-shifted voice signal to a receiving unit, wherein the receiving unit uses the pitch-shifting information to reshift the pitch-shifted voice signal to a second level, wherein the second level is at least substantially equal to the first level.

31. A machine readable storage, having stored thereon a computer program having a plurality of code sections executable by a portable computing device for causing the portable computing device to perform the steps of:

monitoring a pitch of a voice signal;

at a transmitting unit, when the pitch of the voice signal reaches a predetermined threshold, shifting the pitch of the voice signal to at least a portion of a predetermined range; and

transmitting the pitch-shifted voice signal to a receiving unit;

wherein at the receiving unit, the pitch-shifted voice signal is reshifted to a level that compensates the step of shifting the pitch of the voice signal at the transmitting unit.

32. The machine readable storage according to claim 31, wherein the voice signal is comprised of a plurality of time-based frames and wherein the code sections further cause the portable computing device to perform the steps of:

estimating the pitch of the voice signal for at least a portion of the time-based frames of the voice signal; and

based on the estimating step, generating a pitch contour of the voice signal.

33. The machine readable storage according to claim 31, wherein the code sections further cause the portable computing device to perform the steps of:

in the transmitting unit, detecting speech on the voice signal; and

when detecting speech on the voice signal, determining whether the speech is comprised of voiced and unvoiced portions.

34. The machine readable storage according to claim 31, wherein if no speech is detected on the voice signal, the code sections further cause the portable computing device to perform the step of inserting at least one silence frame into the voice signal.

35. The machine readable storage according to claim 34, wherein the code sections further cause the portable computing device to perform the step of converting at least one of the silence frames to a pitch frame, wherein the pitch frames signal the receiving unit that the pitch-shifted voice signal was pitch shifted.

36. The machine readable storage according to claim 34, wherein the code sections further cause the portable computing device to perform the step of adding at least one pitch frame to the voice signal, wherein the pitch frames signal the receiving unit that the pitch-shifted voice signal was pitch shifted.