Packet Loss Concealment Based On Forced Waveform Alignment After Packet Loss

• US 20080046235A1
• Filed: 07/31/2007
• Published: 02/21/2008
• Est. Priority Date: 08/15/2006
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Chen, Juin-Hwey
• Granted Patent: US 8,346,546 B2
• Time in Patent Office: Days
• US Class Current: 704/228
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm

Abstract

A packet loss concealment method and system is described that attempts to reduce or eliminate destructive interference that can occur when an extrapolated waveform representing a lost segment of a speech or audio signal is merged with a good segment after a packet loss. This is achieved by guiding a waveform extrapolation that is performed to replace the bad segment using a waveform available in the first good segment or segments after the packet loss. In another aspect of the invention, a selection is made between a packet loss concealment method that performs the aforementioned guided waveform extrapolation and one that does not. The selection may be made responsive to determining whether the first good segment or segments after the packet loss are available and also to whether a segment preceding the lost segment and the first good segment following the lost segment are deemed voiced.

Claims

1. A method for concealing a lost segment in a speech or audio signal that comprises a series of segments, the method comprising:

(a) generating an extrapolated waveform based on a segment that precedes the lost segment in the series of segments and on one or more segments that follow the lost segment in the series of segments;

(b) generating a replacement waveform for the lost segment based on a first portion of the extrapolated waveform; and

(c) overlap-adding a second portion of the extrapolated waveform with a decoded waveform associated with the one or more segments following the lost segment in the series of segments.

2. The method of claim 1, wherein step (a) comprises:

performing a first-pass periodic waveform extrapolation using a pitch period associated with the segment that precedes the lost segment to generate a first-pass extrapolated waveform;

identifying a time lag between the first-pass extrapolated waveform and the decoded waveform associated with the one or more segments that follow the lost segment;

calculating a pitch contour based on the identified time lag; and

performing a second-pass periodic waveform extrapolation using the pitch contour to generate the extrapolated waveform.

3. The method of claim 2, wherein identifying a time lag between the first-pass extrapolated waveform and a decoded waveform associated with the one or more segments that follow the lost segment comprises:

locating a peak of an energy-normalized cross-correlation function between the first-pass extrapolated waveform and the decoded waveform associated with the one or more segments that follow the lost segment.

4. The method of claim 2, wherein calculating a pitch contour comprises determining an amount of pitch period change per sample.

5. The method of claim 4, wherein determining an amount of pitch period change per sample comprises calculating:

$\mathrm{\delta <br><br>}=\frac{2<br><br>l}{\left(N+1\right)<br><br>\left(2<br><br>g-N<br><br><br><br>p_0-2<br><br>l\right)+2<br><br>l},$

wherein δ

is the amount of pitch period change per sample, l is the identified time lag, p₀ is the pitch period associated with the segment that precedes the lost segment, g is a number of samples from the end of the segment that precedes the lost segment to a middle of an overlap-add region in the first of the one or more segments that follow the lost segment, and N is an integer portion of a number of pitch cycles in the first-pass extrapolated waveform from the end of the segment that precedes the lost segment to the middle of the overlap-add region in the first of the one or more segments that follow the lost segment.

6. The method of claim 1, further comprising:

determining if the one or more segments that follow the lost segment are available; and

performing steps (a), (b) and (c) responsive only to a determination that the one or more segments that follow the lost segment are available.

7. The method of claim 6, further comprising:

performing a packet loss concealment technique that generates an extrapolated waveform based on the segment that precedes the lost segment in the series of segments but not on any segment that follows the lost segment in the series of segments responsive to a determination that the one or more segments that follow the lost segment are not available.

8. The method of claim 6, further comprising:

determining if the segment that precedes the lost segment and the first of the one or more segments that follow the lost segment are deemed voiced segments; and

performing steps (a), (b) and (c) responsive only to a determination that the one or more segments that follow the lost segment are available and that the segment that precedes the lost segment and the first of the one or more segments that follow the lost segment are deemed voiced segments.

9. The method of claim 2, wherein performing a second-pass periodic waveform extrapolation using the pitch contour to generate the extrapolated waveform comprises calculating a scaling factor in accordance with:

c=r^1/m,

or a mathematically equivalent formula, wherein c is the scaling factor, m is a number of pitch cycles in a gap that extends from the end of the segment that precedes the lost segment to a middle of an overlap-add region in the first of the one or more segments that follow the lost segment, and r is a ratio of an average magnitude of a decoded waveform in a target matching window over an average magnitude of a waveform that is m pitch periods earlier.

10. A computer program product comprising a computer-readable medium having computer program logic recorded thereon for enabling a processor to conceal a lost segment in a speech or audio signal that comprises a series of segments, the computer program logic comprising:

first means for enabling the processor to generate an extrapolated waveform based on a segment that precedes the lost segment in the series of segments and on one or more segments that follow the lost segment in the series of segments;

second means for enabling the processor to generate a replacement waveform for the lost segment based on a first portion of the extrapolated waveform; and

third means for enabling the processor to overlap-add a second portion of the extrapolated waveform with a decoded waveform associated with the one or more segments following the lost segment in the series of segments.

11. The computer program product of claim 10, wherein the first means comprises:

means for enabling the processor to perform a first-pass periodic waveform extrapolation using a pitch period associated with the segment that precedes the lost segment to generate a first-pass extrapolated waveform;

means for enabling the processor to identify a time lag between the first-pass extrapolated waveform and the decoded waveform associated with the one or more segments that follow the lost segment;

means for enabling the processor to calculate a pitch contour based on the identified time lag; and

means for enabling the processor to perform a second-pass periodic waveform extrapolation using the pitch contour to generate the extrapolated waveform.

12. The computer program product of claim 11, wherein means for enabling the processor to identifying a time lag between the first-pass extrapolated waveform and a decoded waveform associated with the one or more segments that follow the lost segment comprises:

means for enabling the processor to locate a peak of an energy-normalized cross-correlation function between the first-pass extrapolated waveform and the decoded waveform associated with the one or more segments that follow the lost segment.

13. The computer program product of claim 11, wherein the means for enabling the processor to calculate a pitch contour comprises means for enabling the processor to determine an amount of pitch period change per sample.

14. The computer program product of claim 13, wherein the means for enabling the processor to determine an amount of pitch period change per sample comprises means for enabling the processor to calculate:

$\mathrm{\delta <br><br>}=\frac{2<br><br>l}{\left(N+1\right)<br><br>\left(2<br><br>g-N<br><br><br><br>p_0-2<br><br>l\right)+2<br><br>l},$

wherein δ

is the amount of pitch period change per sample, l is the identified time lag, p₀ is the pitch period associated with the segment that precedes the lost segment, g is a number of samples from the end of the segment that precedes the lost segment to a middle of an overlap-add region in the first of the one or more segments that follow the lost segment, and N is an integer portion of a number of pitch cycles in the first-pass extrapolated waveform from the end of the segment that precedes the lost segment to the middle of the overlap-add region in the first of the one or more segments that follow the lost segment.

15. The computer program product of claim 10, further comprising:

means for enabling the processor to determine if the one or more segments that follow the lost segment in the series of segments are available; and

means for enabling the processor to invoke the first means, second means and third means responsive only to a determination that the one or more segments that follow the lost segment are available.

16. The computer program product of claim 15, further comprising:

means for enabling the processor to perform a packet loss concealment technique that generates an extrapolated waveform based on the segment that precedes the lost segment but not on any segment that follows the lost segment in the series of segments responsive to a determination that the one or more segments that follow the lost segment are not available.

17. The computer program product of claim 15, further comprising:

means for enabling the processor to determine if the segment that precedes the lost segment and the first of the one or more segments that follow the lost segment are deemed voiced segments; and

means for enabling the processor to invoke the first means, second means and third means responsive only to a determination that the one or more segments that follow the lost segment are available and that the segment that precedes the lost segment and the first of the one or more segments that follow the lost segment are deemed voiced segments.

18. The computer program product of claim 11, wherein the means for enabling the processor to perform a second-pass periodic waveform extrapolation using the pitch contour to generate the extrapolated waveform comprises:

means for calculating a scaling factor in accordance with;

c=r^1/m,

or a mathematically equivalent formula, wherein c is the scaling factor, m is a number of pitch cycles in a gap that extends from the end of the segment that precedes the lost segment to a middle of an overlap-add region in the first of the one or more segments that follow the lost segment, and r is a ratio of an average magnitude of a decoded waveform in a target matching window over an average magnitude of a waveform that is m pitch periods earlier.

19. A method for concealing a lost segment in a speech or audio signal that comprises a series of segments, the method comprising:

determining if one or more segments that follow the lost segment in the series of segments are available;

performing packet loss concealment using periodic waveform extrapolation based on a segment that precedes the lost segment in the series of segments and on the one or more segments that follow the lost segment responsive to a determination that the one or more segments that follow the lost segment are available; and

performing packet loss concealment using waveform extrapolation based on the segment that precedes the lost segment but not on any segments that follow the lost segment responsive to a determination that the one or more segments that follow the lost segment are not available.

20. The method of claim 19, further comprising:

determining if the segment that precedes the lost segment and the first of the one or more segments that follow the lost segments are deemed voiced segments; and

performing packet loss concealment using periodic waveform extrapolation based on the segment that precedes the lost segment and on the one or more segments that follow the lost segment responsive to a determination that the one or more segments that follow the lost segment are available and to a determination that the segment that precedes the lost segment and the first of the one or more segments that follow the lost segment are deemed voiced segments; and

performing packet loss concealment using waveform extrapolation based on the segment that precedes the lost segment but not on any segments that follow the lost segment responsive to a determination that the one or more segments that follow the lost segment are not available or to a determination that either the segment that precedes the lost segment or the first of the one or more segments that follow the lost segment is not deemed a voiced segment.

21. A computer program product comprising a computer-readable medium having computer program logic recorded thereon for enabling a processor to conceal a lost segment in a speech or audio signal that comprises a series of segments, the computer program logic comprising:

first means for enabling the processor to determine if one or more segments that follow the lost segment in the series of segments are available;

second means for enabling the processor to perform packet loss concealment using periodic waveform extrapolation based on a segment that precedes the lost segment in the series of segments and on the one or more segments that follow the lost segment responsive to a determination that the one or more segments that follow the lost segment are available; and

third means for enabling the processor to perform packet loss concealment using waveform extrapolation based on the segment that precedes the lost segment but not on any segments that follow the lost segment responsive to a determination that the one or more segments that follow the lost segment are not available.

22. The computer program product of claim 21, further comprising:

means for enabling the processor to determine if the segment that precedes the lost segment and the first of the one or more segments that follow the lost segments are deemed voiced segments;

wherein the second means comprises means for enabling the processor to perform packet loss concealment using periodic waveform extrapolation based on the segment that precedes the lost segment and on the one or more segments that follow the lost segment responsive to a determination that the one or more segments that follow the lost segment are available and to a determination that the segment that precedes the lost segment and the first of the one or more segments that follow the lost segment are deemed voiced segments, and

wherein the third means comprises means for enabling the processor to perform packet loss concealment using waveform extrapolation based on the segment that precedes the lost segment but not on any segments that follow the lost segment responsive to a determination that the one or more segments that follow the lost segment are not available or to a determination that either the segment that precedes the lost segment or the first of the one or more segments that follow the lost segment is not deemed a voiced segment.