BIT ERROR CONCEALMENT FOR AUDIO CODING SYSTEMS

• US 20090281797A1
• Filed: 04/28/2009
• Published: 11/12/2009
• Est. Priority Date: 05/09/2008
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Chen, Juin-Hwey, Kumar, Vivek, Zopf, Robert W.
• Granted Patent: US 8,301,440 B2
• Time in Patent Office: Days
• US Class Current: 704/207
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm

Abstract

A bit error concealment (BEC) system and method is described herein that detects and conceals the presence of click-like artifacts in an audio signal caused by bit errors introduced during transmission of the audio signal within an audio communications system. A particular embodiment of the present invention utilizes a low-complexity design that introduces no added delay and that is particularly well-suited for applications such as Bluetooth® wireless audio devices which have low cost and low power dissipation requirements.

Claims

1. A method for performing bit error concealment in an audio receiver, comprising:

decoding a portion of an encoded bit stream to generate a decoded audio frame, wherein the decoded audio frame comprises a portion of a decoded audio signal;

analyzing at least the decoded audio signal to detect whether the decoded audio frame includes a distortion that will be audible during playback thereof, the distortion being due to bit errors in the encoded bit stream; and

responsive to detecting that the decoded audio frame includes the distortion, performing operations on the decoded audio signal to conceal the distortion.

2. The method of claim 1, wherein the step of decoding the portion of the encoded bit stream is performed by one of:

a Continuously Variable Slope Delta Modulation (CVSD) decoder;

a pulse code modulation (PCM) decoder;

a G.711 decoder;

or

a sub-band codec (SBC) decoder.

3. The method of claim 1, wherein analyzing at least the decoded audio signal to detect whether the decoded audio frame includes the distortion comprises:

determining if a maximum absolute sample value in a segment of a prediction residual that is associated with the decoded audio frame exceeds an average signal level of the prediction residual for the decoded audio frame multiplied by an adaptive threshold.

4. The method of claim 3 further comprising:

obtaining the prediction residual by performing short term prediction and long term prediction.

5. The method of claim 3, further comprising:

determining the average signal level of the prediction residual for the decoded audio frame by computing an average magnitude of the prediction residual for the decoded audio frame.

6. The method of claim 3, further comprising:

determining the average signal level of the prediction residual for the decoded audio frame by computing an energy level of the prediction residual for the decoded audio frame.

7. The method of claim 1, wherein analyzing at least the decoded audio signal to detect whether the decoded audio frame includes the distortion comprises:

analyzing a pitch history of the decoded audio signal;

assigning the pitch history to one of a plurality of pitch track categories based on the analysis; and

modifying a sensitivity level for detecting whether the decoded audio frame includes the distortion based on the pitch track category assigned to the pitch history.

8. The method of claim 1, wherein analyzing at least the decoded audio signal to detect whether the decoded audio frame includes the distortion comprises:

computing a plurality of pitch predictor taps associated with the decoded audio frame; and

modifying a sensitivity level for detecting whether the decoded audio frame includes the distortion based on a difference between a sum of the plurality of pitch predictor taps associated with the decoded audio frame and a sum of a plurality of pitch predictor taps associated with a previously-decoded audio frame.

9. The method of claim 1, wherein analyzing at least the decoded audio signal to detect whether the decoded audio frame includes the distortion comprises:

calculating a voicing strength measure associated with the decoded audio frame; and

modifying a sensitivity level for detecting whether the decoded audio frame includes the distortion based on the voicing strength measure.

10. The method of claim 1, wherein performing operations on the decoded audio signal to conceal the distortion comprises replacing the decoded audio frame with a synthesized audio frame generated in accordance with a packet loss concealment algorithm.

11. The method of claim 10, further comprising:

performing a state memory update of an audio decoder based on re-encoding of the synthesized audio frame responsive to at least detecting that the decoded audio frame includes the distortion.

12. The method of claim 11, further comprising performing the state memory update of the audio decoder based on re-encoding of the synthesized audio frame responsive to detecting that the decoded audio frame includes the distortion and determining that the decoded audio signal represents background noise.

13. The method of claim 1, further comprising:

analyzing non-speech segments of the decoded audio signal to estimate a rate at which audible distortions are detected; and

adapting a biasing factor based on the estimated rate, wherein the biasing factor is used to determine a sensitivity level for detecting whether the decoded audio frame includes the distortion.

14. The method of claim 13, wherein analyzing non-speech segments of the decoded audio signal to estimate a rate at which audible distortions are detected includes:

limiting the estimated rate to a function of a received packet loss rate.

15. The method of claim 1, further comprising:

analyzing non-speech segments of the decoded audio signal to estimate a rate at which audible distortions are detected;

determining whether the estimated rate is below a predefined threshold; and

responsive to determining that the estimated rate is below the predefined threshold, disabling at least a component configured to perform the analysis of the decoded audio signal to detect whether the decoded audio frame includes the distortion.

16. A system, comprising:

an audio decoder configured to decode a portion of an encoded bit stream to generate a decoded audio frame, wherein the decoded audio frame comprises a portion of a decoded audio signal;

a bit error detection module configured to analyze at least the decoded audio signal to detect whether the decoded audio frame includes a distortion that will be audible during playback thereof, the distortion being due to bit errors in the encoded bit stream; and

a concealment module configured to perform operations on the decoded audio signal to conceal the distortion responsive to detection of the distortion within the decoded audio frame.

17. The system of claim 16, wherein the audio decoder comprises one of:

a Continuously Variable Slope Delta Modulation (CVSD) decoder;

a pulse code modulation (PCM) decoder;

a G.711 decoder;

or

a sub-band codec (SBC) decoder.

18. The system of claim 16, wherein the bit error detection module is configured to analyze at least the decoded audio signal to detect whether the decoded audio frame includes the distortion by determining if a maximum absolute sample value in a segment of a prediction residual that is associated with the decoded audio frame exceeds an average signal level of the prediction residual for the decoded audio frame multiplied by an adaptive threshold.

19. The system of claim 18, wherein the bit error detection module is configured to determine the average signal level of the prediction residual for the decoded audio frame by computing an average magnitude of the prediction residual for the decoded audio frame.

20. The system of claim 18, wherein the bit error detection module is configured to determine the average signal level of the prediction residual for the decoded audio frame by computing an energy level of the prediction residual for the decoded audio frame.

21. The system of claim 16, wherein the bit error detection module is configured to analyze at least the decoded audio signal to detect whether the decoded audio frame includes the distortion by analyzing a pitch history of the decoded audio signal, assigning the pitch history to one of a plurality of pitch track categories based on the analysis, and modifying a sensitivity level for detecting whether the decoded audio frame includes the distortion based on the pitch track category assigned to the pitch history.

22. The system of claim 16, wherein the bit error detection module is configured to analyze at least the decoded audio signal to detect whether the decoded audio frame includes the distortion by computing a plurality of pitch predictor taps associated with the decoded audio frame and modifying a sensitivity level for detecting whether the decoded audio frame includes the distortion based on a difference between a sum of the plurality of pitch predictor taps associated with the decoded audio frame and a sum of a plurality of pitch predictor taps associated with a previously-decoded audio frame.

23. The system of claim 16, wherein the bit error detection module is configured to analyze at least the decoded audio signal to detect whether the decoded audio frame includes the distortion by calculating a voicing strength measure associated with the decoded audio frame and modifying a sensitivity level for detecting whether the decoded audio frame includes the distortion based on the voicing strength measure.

24. The system of claim 16, wherein the concealment module is configured to perform operations on the decoded audio signal to conceal the distortion by replacing the decoded audio frame with a synthesized audio frame generated in accordance with a packet loss concealment algorithm.

25. The system of claim 24, further comprising:

a re-encoding module configured to perform a state memory update of the audio decoder based on re-encoding of the synthesized audio frame responsive to at least detection of the distortion within the decoded audio frame.

26. The system of claim 25, wherein the re-encoding module is configured to perform the state memory update of the audio decoder based on re-encoding of the synthesized audio frame responsive to at least detection of the distortion within the decoded audio frame and to determining that the decoded audio signal represents background noise.

27. The system of claim 16, further comprising:

a threshold biasing module configured to analyze non-speech segments of the decoded audio signal to estimate a rate at which audible distortions are detected and to adapt a biasing factor based on the estimated rate, wherein the biasing factor is used by the bit error detection module to determine a sensitivity level for detecting whether the decoded audio frame includes the distortion.

28. The system of claim 27, wherein the threshold biasing module is configured to estimate the rate at which audible distortions are detected by limiting the estimated rate to a function of a received packet loss rate.

29. The system of claim 16, further comprising:

a threshold biasing module configured to analyze non-speech segments of the decoded audio signal to estimate a rate at which audible distortions are detected, to determine whether the estimated rate is below a predefined threshold and to disable at least the bit error detection module responsive to determining that the estimated rate is below the predefined threshold.

30. A computer program product comprising a computer-readable medium having computer program logic recorded thereon for enabling a processing unit to perform bit error concealment, the computer program logic comprising:

first means for enabling the processing unit to decode a portion of an encoded bit stream to generate a decoded audio frame, wherein the decoded audio frame comprises a portion of a decoded audio signal;

second means for enabling the processing unit to analyze at least the decoded audio signal to detect whether the decoded audio frame includes a distortion that will be audible during playback thereof, the distortion being due to bit errors in the encoded bit stream; and

third means for enabling the processing unit to perform operations on the decoded audio signal to conceal the distortion responsive to detection of the distortion within the decoded audio frame.