Robust decoder

• US 20060271373A1
• Filed: 05/31/2005
• Published: 11/30/2006
• Est. Priority Date: 05/31/2005
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Sun, Xiaoqin, Khalil, Hosam A., Chen, Wei-Ge, Koishida, Kazuhito, Wang, Tian
• Granted Patent: US 7,831,421 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 21/045 using thinning out or insertion of a waveform

Abstract

Techniques and tools related to delayed or lost coded audio information are described. For example, a concealment technique for one or more missing frames is selected based on one or more factors that include a classification of each of one or more available frames near the one or more missing frames. As another example, information from a concealment signal is used to produce substitute information that is relied on in decoding a subsequent frame. As yet another example, a data structure having nodes corresponding to received packet delays is used to determine a desired decoder packet delay value.

Claims

1. A computer-implemented method comprising:

processing a bit stream for an audio signal, including, if one or more missing frames is encountered while processing the bit stream,

based at least in part on one or more factors, selecting a concealment technique from among multiple available signal-dependent concealment techniques; and

performing the selected concealment technique; and

outputting a result.

2. The method of claim 1 wherein the one or more factors comprise a classification of an available frame prior to the one or more missing frames in the audio signal, and wherein the classification is one of a set of possible classifications comprising voiced and unvoiced.

3. The method of claim 2 wherein:

if the classification of the available prior frame is voiced, then the selected concealment technique comprises using a pitch extension technique to generate a concealment signal; and

if the classification of the available prior frame is unvoiced, then the selected concealment technique comprises generating the concealment signal based at least in part on energy of the available prior frame.

4. The method of claim 2, wherein the one or more factors further comprises a count of the one or more missing frames, the count indicating how many consecutive frames are missing.

5. The method of claim 4, wherein:

if the classification of the available prior frame and a classification of an available frame following the one or more missing frames in the audio signal are both voiced, and the count of the one or more missing frames is less than a threshold value, then the selected concealment technique comprises bi-directional concealment; and

if the classification of the available prior frame is voiced, and the count of the one or more missing frames is more than a threshold value, then the selected concealment technique comprises unidirectional concealment.

6. The method of claim 2, wherein if the classification of the available prior frame is voiced, then the selected concealment technique comprises adding noise to a concealment signal if the concealment signal is longer than a threshold duration.

7. The method of claim 2, wherein if the classification of the available prior frame is unvoiced, then the selected concealment technique comprises:

identifying multiple segments of the available prior frame;

using the multiple prior frame segments to generate multiple concealment signal segments; and

merging the multiple prior frame segments together with the multiple concealment segments to generate a concealment signal.

8. The method of claim 1, wherein the selected concealment technique comprises:

generating an extension signal; and

adding noise to the extension signal to produce a concealment signal.

9. The method of claim 8, wherein the selected concealment technique further comprises:

gradually decreasing energy of the extension signal along at least part of the audio signal; and

gradually increasing energy of the noise along the at least part of the audio signal.

10. The method of claim 1 wherein the multiple available signal-dependent concealment techniques include a unidirectional concealment technique for voiced content, a unidirectional concealment technique for unvoiced content, a bi-directional concealment technique, and a fading concealment technique.

11. The method of claim 1 wherein the one or more factors include classification of an available prior frame, classification of an available following frame, and a count of missing frames between the available prior frame and the available following frame in the audio signal.

12. A computer-implemented method comprising:

when encountering one or more frames missing from a bit stream for an audio signal, generating a concealment signal based at least in part on pitch cycles in one or more previous frames, including introducing pitch jitter; and

outputting a result.

13. The method of claim 12 wherein the introducing pitch jitter includes adding random or pseudorandom factors to pitch for the concealment signal

14. The method of claim 13, wherein the random or pseudorandom factors include positive and negative values.

15. The method of claim 13, wherein a separate random or pseudorandom factor is applied to each of plural parts of the concealment signal.

16. The method of claim 12, wherein the introducing includes increasing the pitch jitter as distance away from the one or more previous frames increases.

17. A computer-implemented method comprising:

encountering one or more frames missing from a bit stream for an audio signal;

producing a concealment signal;

encountering a subsequent frame that relies at least in part on information from the one or more missing frames for decoding;

producing substitute information from the concealment signal; and

relying on the substitute information in place of the information from the one or more missing frames to decode the subsequent frame.

18. The method of claim 17, wherein an adaptive codebook index of the subsequent frame indicates a segment of the one or more missing frames to be used in computing an adaptive codebook contribution to at least a portion of an excitation signal of the subsequent frame.

19. The method of claim 17, wherein producing the substitute information comprises at least partially encoding at least a portion of the concealment signal.

20. The method of claim 17, wherein producing the substitute information comprises constructing information representing a residual signal based on the concealment signal.