Method and apparatus for performing packet loss or frame erasure concealment

• US 8,423,358 B2
• Filed: 05/21/2012
• Issued: 04/16/2013
• Est. Priority Date: 04/19/1999
• Status: Expired due to Fees

• Current Assignee: AT&T Intellectual Property I LP (AT&T, Inc.)
• Original Assignee: AT&T Intellectual Property I LP (AT&T, Inc.)
• Inventors: Kapilow, David A.
• Primary Examiner(s): Abebe, Daniel D
• Application Number:
  US13/476,932
• Publication Number:
  US 20120232889A1
• Time in Patent Office: 330 Days
• Field of Search: 704/228, 704/267, 370/281, 714/776
• US Class Current: 704/228
• CPC Class Codes: G10L 19/0017 Lossless audio signal coding; Perfect reconstruction of coded audio signal by transmission of coding error G10L19/24 takes precedence
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 19/028 Noise substitution, i.e. substituting non-tonal spectral components by noisy source comfort noise for discontinuous speech transmission G10L19/012
• CPC Class Codes: G10L 21/003 Changing voice quality, e.g. pitch or formants

Abstract

A method for performing packet loss or Frame Erasure Concealment (FEC) for a speech coder receives encoded frames of compressed speech information transmitted from an encoder. The method determines whether an encoded frame has been lost, corrupted in transmission, or erased, synthesizes properly received frames, and decides on an overlap-add window to use in combining a portion of the synthesized speech signal with a subsequent speech signal resulting from a received and decoded packet, where the size of the overlap-add window is based on the unavailability of packets. If it is determined that an encoded frame has been lost, corrupted in transmission, or erased, the method performed an overlap-add operation on the portion of the synthesized speech signal and the subsequent speech signal, using the decided-on overlap-add window.

Claims

1. A method for creating an output signal in response to determining one or more unexpected packets, where an unexpected packet includes a packet that is lost, corrupted, erased or delayed, and where an expected packet includes a packet that is not lost, corrupted, erased or delayed, the method comprising:

generating at least one synthesized audio signal segment corresponding to at least one unexpected packet;

determining a length of an overlap-add window to use in combining the at least one synthesized audio signal segment with a subsequent audio signal segment resulting from an expected packet being decoded by a receiver, wherein the expected packet is received subsequent to the at least one unexpected packet, wherein the length of the overlap-add window is determined based on a length of an erasure encompassing the at least one unexpected packet; and

performing an overlap-add operation on the at least one synthesized audio signal segment and the subsequent audio signal segment using the determined length of the overlap-add window.

2. The method of claim 1, wherein the at least one synthesized audio signal segment comprises a plurality of synthesized audio signal segments R_j−

1, R<sub>j−

2</sub>, . . . R<sub>j−

k</sub>, corresponding to a plurality of unexpected packets of the at least one unexpected packet, wherein the audio signal segment is represented by R_j, wherein a modified audio signal segment, R_j is created from the overlap-add operation and represents the output signal.

3. The method of claim 2, where the length of the overlap-add window is represented by:

4. The method of claim 1 where, when the length of the erasure exceeds 10 msec, the audio signal segment R_j−

1 is attenuated before performing the overlap-add operation.

5. The method of claim 4, wherein the audio signal segment R_j−

1 is attenuated by a predefined percentage.

6. The method of claim 1 where, when the length of the erasure does not exceed 10 msec, the audio signal segment R_j−

1 is not attenuated before performing the overlap-add operation.

7. The method of claim 1, wherein the length of the overlap-add window is increased by a predefined time duration for each additional unexpected packet in the length of an erasure.

8. The method of claim 7, wherein the predefined time duration comprises 4 msec.

9. The method of claim 7, wherein the length of the overlap-add window is increased up to a predefined maximum time duration.

10. The method of claim 7, wherein the predefined maximum time duration comprises 10 msec.

11. A receiver for executing a method for creating an output signal in response to determining one or more unexpected packets, where an unexpected packet includes a packet that is lost, corrupted, erased or delayed, and where an expected packet includes a packet that is not lost, corrupted, erased or delayed, the method comprising:

generating at least one synthesized audio signal segment corresponding to at least one unexpected packet;

determining a length of an overlap-add window to use in combining the at least one synthesized audio signal segment with a subsequent audio signal segment resulting from an expected packet being decoded by a receiver, wherein the expected packet is received subsequent to the at least one unexpected packet, wherein the length of the overlap-add window is determined based on a length of an erasure encompassing the at least one unexpected packet; and

performing an overlap-add operation on the at least one synthesized audio signal segment and the subsequent audio signal segment using the determined length of the overlap-add window.

12. The receiver of claim 11, wherein the at least one synthesized audio signal segment comprises a plurality of synthesized audio signal segments R_j−

1, R<sub>j−

2</sub>, . . . R<sub>j−

k</sub>, corresponding to a plurality of unexpected packets of the at least one unexpected packet, wherein the audio signal segment is represented by R_j, wherein a modified audio signal segment, R′

_j is created from the overlap-add operation and represents the output signal.

13. The receiver of claim 12, where the length of the overlap-add window is represented by:

14. The receiver of claim 11 where, when the length of the erasure exceeds 10 msec, the audio signal segment R_j−

1 is attenuated before performing the overlap-add operation.

15. The receiver of claim 14, wherein the audio signal segment R_j−

1 is attenuated by a predefined percentage.

16. The receiver of claim 11 where, when the length of the erasure does not exceed 10 msec, the audio signal segment R_j−

1 is not attenuated before performing the overlap-add operation.

17. The receiver of claim 11, wherein the length of the overlap-add window is increased by a predefined time duration for each additional unexpected packet in the length of an erasure.

18. The receiver of claim 17, wherein the predefined time duration comprises 4 msec.

19. The receiver of claim 17, wherein the length of the overlap-add window is increased up to a predefined maximum time duration.

20. The receiver of claim 17, wherein the predefined maximum time duration comprises 10 msec.