Method and device for frequency-selective pitch enhancement of synthesized speech

• US 7,529,660 B2
• Filed: 05/30/2003
• Issued: 05/05/2009
• Est. Priority Date: 05/31/2002
• Status: Active Grant

• Current Assignee: VoiceAge Corporation
• Original Assignee: VoiceAge Corporation
• Inventors: Bessette, Bruno, Lefebvre, Roch, Laflamme, Claude, Jelinek, Milan
• Primary Examiner(s): Lerner; Martin
• Application Number:
  US10/515,553
• Publication Number:
  US 20050165603A1
• Time in Patent Office: 2,167 Days
• Field of Search: 704/205, 704/206, 704/207, 704/226, 704/227, 704/228, 704/500, 704/501, 704/502
• US Class Current: 704/205
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 21/0232 Processing in the frequency domain
• CPC Class Codes: G10L 21/0364 for improving intelligibility

Abstract

In a method and device for post-processing a decoded sound signal in view of enhancing a perceived quality of this decoded sound signal, the decoded sound signal is divided into a plurality of frequency sub-band signals, and post-processing is applied to at least one of the frequency sub-band signal. After post-processing of this at least one frequency sub-band signal, the frequency sub-band signals may be added to produce an output post-processed decoded sound signal. In this manner, the post-processing can be localized to a desired sub-band or sub-bands with leaving other sub-bands virtually unaltered.

Claims

1. A method for post-processing a decoded sound signal in view of enhancing a perceived quality of said decoded sound signal, comprising:

dividing the decoded sound signal into a plurality of frequency sub-band signals; and

applying post-processing to only a part of the frequency sub-band signals;

wherein applying post-processing to only a part of the frequency sub-band signals comprises pitch enhancing the frequency sub-band signals only in a lower frequency band of the decoded sound signal.

2. A post-processing method as defined in claim 1, further comprising summing the frequency sub-band signals, after post-processing of said part of the frequency sub-band signals, to produce an output post-processed decoded sound signal.

3. A post-processing method as defined in claim 1, wherein pitch enhancing comprises adaptively filtering said part of the frequency sub-band signals.

4. A post-processing method as defined in claim 1, wherein dividing the decoded sound signal into a plurality of frequency sub-band signals comprises sub-band filtering the decoded sound signal to produce the plurality of frequency sub-band signals.

5. A post-processing method as defined in claim 1, wherein, for said part of the frequency sub-band signals:

pitch enhancing comprises adaptively filtering the decoded sound signal; and

dividing the decoded sound signal comprises sub-band filtering the adaptively filtered decoded sound signal.

6. A post-processing method as defined in claim 1, wherein:

dividing the decoded sound signal into a plurality of frequency sub-band signals comprises;

a high-pass filtering of the decoded sound signal to produce a frequency high-band signal; and

a first low-pass filtering of the decoded sound signal to produce a frequency low-band signal; and

pitch enhancing comprises;

pitch enhancing the decoded sound signal prior to the first low-pass filtering of the decoded sound signal to produce the frequency low-band signal.

7. A post-processing method as defined in claim 6, further comprising a second low-pass filtering of the decoded sound signal prior to pitch enhancing said decoded sound signal.

8. A post-processing method as defined in claim 6, further comprising summing the frequency high-band and low-band signals to produce an output post-processed decoded sound signal.

9. A post-processing method as defined in claim 1, wherein:

dividing the decoded sound signal into a plurality of frequency sub-band signals comprises;

band-pass filtering the decoded sound signal to produce a frequency upper-band signal; and

low-pass filtering the decoded sound signal to produce a frequency lower-band signal; and

pitch enhancing comprises;

pitch enhancing the decoded sound signal prior to low-pass filtering the decoded sound signal to produce a frequency lower-band signal.

10. A post-processing method as defined in claim 9, further comprising summing the frequency upper-band and lower-band signals to produce an output post-processed decoded sound signal.

11. A post-processing method as defined in claim 1, wherein:

dividing the decoded sound signal into a plurality of frequency sub-band signals comprises;

low-pass filtering the decoded sound signal to produce a frequency low-band signal; and

pitch enhancing comprises;

pitch enhancing the frequency low-band signal.

12. A post-processing method as defined in claim 11, wherein pitch enhancing comprises processing the decoded sound signal through an inter-harmonic filter for inter-harmonic attenuation of the decoded sound signal.

13. A post-processing method as defined in claim 12, wherein pitch enhancing comprises multiplying the inter-harmonic filtered decoded sound signal by an adaptive pitch enhancement gain.

14. A post-processing method as defined in claim 12, further comprising low-pass filtering the decoded sound signal prior to processing the decoded sound signal through the inter-harmonic filter.

15. A post-processing method as defined in claim 11, further comprising summing the decoded sound signal and the frequency low-band signal to produce an output post-processed decoded sound signal.

16. A post-processing method as defined in claim 11, wherein pitch enhancing comprises processing the decoded sound signal through an inter-harmonic filter having the following transfer function:

$y<br><br>\left[n\right]=\frac{1}{2}<br><br>x<br><br>\left[n\right]-\frac{1}{4}<br><br>\left\{x<br><br>\left[n-T\right]+x<br><br>\left[n+T\right]\right\}$

for inter-harmonic attenuation of the decoded sound signal, where x[n] is the decoded sound signal, y[n] is the inter-harmonic filtered decoded sound signal in a given sub-band, and T is a pitch delay of the decoded sound signal.

17. A post-processing method as defined in claim 16, further comprising summing the unprocessed decoded sound signal and the inter-harmonic filtered frequency low-band signal to produce an output post-processed decoded sound signal.

18. A post-processing method as defined in claim 1, wherein pitch enhancing comprises pitch enhancing the decoded sound signal using the following equation:

$y<br><br>\left[n\right]=\left(1-\frac{\mathrm{\alpha <br><br>}}{2}\right)<br><br>x<br><br>\left[n\right]+\frac{\mathrm{\alpha <br><br>}}{4}<br><br>\left\{x<br><br>\left[n-T\right]+x<br><br>\left[n+T\right]\right\}$

where x[n] is the decoded sound signal, y[n] is the pitch enhanced decoded sound signal in a given sub-band, T is a pitch delay of the decoded sound signal, and α

is a coefficient varying between 0 and 1 to control an amount of inter-harmonic attenuation of the decoded sound signal.

19. A post-processing method as defined in claim 18, comprising receiving the pitch delay T through a bitstream.

20. A post-processing method as defined in claim 18, comprising decoding the pitch delay T from a received, encoded bitstream.

21. A post-processing method as defined in claim 18, comprising calculating the pitch delay T in response to the decoded sound signal for an improved pitch tracking.

22. A post-processing method as defined in claim 1, wherein, during encoding, the sound signal is down-sampled from a higher sampling frequency to a lower sampling frequency, and wherein dividing the decoded sound signal into a plurality of frequency sub-band signals comprises up-sampling the decoded sound signal from the lower sampling frequency to the higher sampling frequency.

23. A post-processing method as defined in claim 22, wherein dividing the decoded sound signal into a plurality of frequency sub-band signals comprises sub-band filtering the decoded sound signal, and wherein the up-sampling of the decoded sound signal from the lower sampling frequency to the higher sampling frequency is combined to the sub-band filtering.

24. A post-processing method as defined in claim 22, comprising:

band-pass filtering the decoded sound signal to produce a frequency upper-band signal, said band-pass filtering of the decoded sound signal being combined with up-sampling of the decoded sound signal from the lower sampling frequency to the higher sampling frequency; and

pitch enhancing the decoded sound signal and low-pass filtering the pitch enhanced decoded sound signal to produce a frequency lower-band signal, said low-pass filtering of the pitch enhanced decoded sound signal being combined with up-sampling of the post-processed decoded sound signal from the lower sampling frequency to the higher sampling frequency.

25. post-processing method as defined in claim 24, further comprising adding the frequency upper-band signal with the frequency lower-band signal to form an output post-processed and up-sampled decoded sound signal.

26. A post-processing method as defined in claim 24, wherein pitch enhancing the decoded sound signal comprises processing the decoded sound signal by means of the following equation:

$y<br><br>\left[n\right]=\left(1-\frac{\mathrm{\alpha <br><br>}}{2}\right)<br><br>x<br><br>\left[n\right]+\frac{\mathrm{\alpha <br><br>}}{4}<br><br>\left\{x<br><br>\left[n-T\right]+x<br><br>\left[n+T\right]\right\}$

where x[n] is the decoded sound signal, y[n] is the pitch enhanced decoded sound signal in a given sub-band, T is a pitch delay of the decoded sound signal, and α

is a coefficient varying between 0 and 1 to control an amount of inter-harmonic attenuation of the decoded sound signal.

27. A post-processing method as defined in claim 1, wherein:

dividing the decoded sound signal into a plurality of frequency sub-band signals comprises dividing the decoded sound signal into a frequency upper-band signal and a frequency lower-band signal; and

pitch enhancing comprises pitch enhancing the frequency lower-band signal.

28. A post-processing method as defined in claim 1, wherein pitch enhancing comprises:

determining a pitch value of the decoded sound signal;

calculating, in relation to the determined pitch value, a high-pass filter with a cut-off frequency below a fundamental frequency of the decoded sound signal; and

processing the decoded sound signal through the calculated high-pass filter.

29. A device for post-processing a decoded sound signal in view of enhancing a perceived quality of said decoded sound signal, comprising:

a divider of the decoded sound signal into a plurality of frequency sub-band signals; and

a post-processor of only a part of the frequency sub-band signals;

wherein the post-processor comprises a pitch enhancer of the frequency sub-band signals only in a lower frequency band of the decoded sound signal.

30. A post-processing device as defined in claim 29, further comprising an adder for summing the frequency sub-band signals, after post-processing of said part of the frequency sub-band signals, to produce an output post-processed decoded sound signal.

31. A post-processing device as defined in claim 29, wherein the post-processor comprises an adaptive filter supplied with the decoded sound signal.

32. A post-processing device as defined in claim 29, wherein the divider comprises a sub-band filter supplied with the decoded sound signal.

33. A post-processing device as defined in claim 29, wherein, for said part of the frequency sub-band signals:

the post-processor comprises an adaptive filter supplied with the decoded sound signal to produce an adaptively filtered decoded sound signal; and

the dividing means comprises a sub-band filter supplied with the adaptively filtered decoded sound signal.

34. A post-processing device as defined in claim 29, wherein:

the dividing means comprises;

a high-pass filter supplied with the decoded sound signal to produce a frequency high-band signal; and

a first low-pass filter supplied with the decoded sound signal to produce a frequency low-band signal; and

the pitch enhancer enhances the decoded sound signal prior to low-pass filtering the decoded sound signal through the first low-pass filter.

35. A post-processing device as defined in claim 34, wherein the post-processor further comprises a second low-pass filter supplied with the decoded sound signal to produce a low-pass filtered decoded sound signal supplied to the pitch enhancer.

36. A post-processing device as defined in claim 34,further comprising an adder for summing the frequency high-band and low-band signals to produce an output post-processed decoded sound signal.

37. A post-processing device as defined in claim 29, wherein:

the divider comprises;

a band-pass filter supplied with the decoded sound signal to produce a frequency upper-band signal; and

a low-pass filter supplied with the decoded sound signal to produce a frequency lower-band signal; and

the pitch enhancer enhances the decoded sound signal prior to low-pass filtering the decoded sound signal through the low-pass filter to produce the frequency lower-band signal.

38. A post-processing device as defined in claim 37, wherein the pitch enhancer comprises a pitch filter supplied with the decoded sound signal to produce a pitch enhanced decoded sound signal supplied to the low-pass filter.

39. A post-processing device as defined in claim 37, further comprising an adder for summing the frequency upper-band and lower-band signals to produce an output post-processed decoded sound signal.

40. A post-processing device as defined in claim 29, wherein:

the divider comprises;

a low-pass filter supplied with the decoded sound signal to produce a frequency low-band signal; and

the pitch enhancer enhances the decoded sound signal to produce a post-processed pitch enhanced decoded sound signal supplied to the low-pass filter.

41. A post-processing device as defined in claim 40, wherein the pitch enhancer comprises an inter-harmonic filter supplied with the decoded sound signal to produce an inter-harmonic, attenuated decoded sound signal.

42. A post-processing device as defined in claim 41, wherein the pitch enhancer comprises a multiplier for multiplying the inter-harmonic, attenuated decoded sound signal by an adaptive pitch enhancement gain.

43. A post-processing device as defined in claim 41, further comprising a low-pass filter supplied with the decoded sound signal to produce a low-pass filtered decoded sound signal supplied to the inter-harmonic filter.

44. A post-processing device as defined in claim 40, further comprising an adder for summing the decoded sound signal and the frequency low-band signal to produce an output post-processed decoded sound signal.

45. A post-processing device as defined in claim 40, wherein the pitch enhancer comprises an inter-harmonic filter having the following transfer function:

$y<br><br>\left[n\right]=\frac{1}{2}<br><br>x<br><br>\left[n\right]-\frac{1}{4}<br><br>\left\{x<br><br>\left[n-T\right]+x<br><br>\left[n+T\right]\right\}$

for inter-harmonic attenuating the decoded sound signal, where x[n] is the decoded sound signal, y[n] is the inter-harmonic filtered decoded sound signal in a given sub-band, and T is a pitch delay of the decoded sound signal.

46. A post-processing device as defined in claim 45, further comprising an adder for summing the unprocessed decoded sound signal and the inter-harmonic filtered frequency low-band signal to produce an output post-processed decoded sound signal.

47. A post-processing device as defined in claim 29, wherein the pitch enhancer of the decoded sound signal uses the following equation:

$y<br><br>\left[n\right]=\left(1-\frac{\mathrm{\alpha <br><br>}}{2}\right)<br><br>x<br><br>\left[n\right]+\frac{\mathrm{\alpha <br><br>}}{4}<br><br>\left\{x<br><br>\left[n-T\right]+x<br><br>\left[n+T\right]\right\}$

where x[n] is the decoded sound signal, y[n] is the pitch enhanced decoded sound signal in a given sub-band, T is a pitch delay of the decoded sound signal, and α

is a coefficient varying between 0 and 1 to control an amount of inter-harmonic attenuation of the decoded sound signal.

48. A post-processing device as defined in claim 47, comprising a receiver of the pitch delay T through a bitstream.

49. A post-processing device as defined in claim 47, comprising a decoder of the pitch delay T from a received, encoded bitstream.

50. A post-processing device as defined in claim 47, comprising a calculator of the pitch delay T in response to the decoded sound signal for an improved pitch tracking.

51. A post-processing device as defined in claim 29, wherein, during encoding, the sound signal is down-sampled from a higher sampling frequency to a lower sampling frequency, and wherein the divider comprises an up-sampler of the decoded sound signal from the lower sampling frequency to the higher sampling frequency.

52. A post-processing device as defined in claim 51, wherein the divider comprises a sub-band filter supplied with the decoded sound signal, and wherein the up-sampler is combined with the sub-band filter.

53. A post-processing device as defined in claim 51, wherein:

the pitch enhancer enhances the decoded sound signal; and

the divider comprises;

a band-pass filter supplied with the decoded sound signal to produce a frequency upper-band signal, said band-pass filter being combined with the up-sampler; and

a low-pass filter supplied with the pitch enhanced decoded sound signal to produce a frequency lower-band signal, said low-pass filter being combined with the up-sampler.

54. A post-processing device as defined in claim 53, further comprising an adder for summing the frequency upper-band signal with the frequency lower-band signal to form an output pitch-enhanced and up-sampled decoded sound signal.

55. A post-processing device as defined in claim 53, wherein the pitch enhancer uses the following equation:

$y<br><br>\left[n\right]=\left(1-\frac{\mathrm{\alpha <br><br>}}{2}\right)<br><br>x<br><br>\left[n\right]+\frac{\mathrm{\alpha <br><br>}}{4}<br><br>\left\{x<br><br>\left[n-T\right]+x<br><br>\left[n+T\right]\right\}$

where x[n] is the decoded sound signal, y[n] is the pitch enhanced decoded sound signal in a given sub-band, T is a pitch delay of the decoded sound signal, and α

is a coefficient varying between 0 and 1 to control an amount of inter-harmonic attenuation of the decoded sound signal.

56. A post-processing device as defined in claim 29, wherein:

the divider divides the decoded sound signal into a frequency upper-band signal and a frequency lower-band signal; and

the pitch enhancer enhances the frequency lower-band signal.

57. A post-processing device as defined in claim 29, wherein the pitch enhancer:

determines a pitch value of the decoded sound signal;

calculates, in relation to the determined pitch value, a high-pass filter with a cut-off frequency below a fundamental frequency of the decoded sound signal; and

processes the decoded sound signal through the calculated high-pass filter.

58. A sound signal decoder comprising:

an input for receiving an encoded sound signal;

a parameter decoder supplied with the encoded sound signal for decoding sound signal encoding parameters;

a sound signal decoder supplied with the decoded sound signal encoding parameters for producing a decoded sound signal; and

a post-processing device as recited in any of claims 29 to 57 for post-processing the decoded sound signal in view of enhancing a perceived quality of said decoded sound signal.