Method and apparatus for preserving matrix surround information in encoded audio/video

• US 20030231774A1
• Filed: 11/14/2002
• Published: 12/18/2003
• Est. Priority Date: 04/23/2002
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: RealNetworks, Inc.
• Inventors: Schildbach, Wolfgang A., Cooke, Kenneth Edward
• Granted Patent: US 7,428,440 B2
• Time in Patent Office: Days
• US Class Current: 381/20
• CPC Class Codes: G10L 19/008 Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/167 Audio streaming, i.e. formatting and decoding of an encoded audio signal representation into a data stream for transmission or storage purposes
• CPC Class Codes: H04S 3/02 of the matrix type, i.e. in which input signals are combined algebraically, e.g. after having been phase shifted with respect to each other

Abstract

A method and apparatus for preserving matrix-surround information in encoded audio/video includes a receiver operative to receive matrix-surround encoded audio signals via a modem, separate the audio signals into a frequency spectrum having discrete audio frequencies, and determine a cutoff threshold used to encode the matrix-surround encoded audio signals. The method and apparatus further includes a decoder operative to decode a first set of the audio frequencies below the determined cutoff threshold using a first matrix-surround preserving audio encoding method and to decode a second set of audio frequencies above the cutoff threshold using a second non matrix-surround preserving audio encoding method.

Claims

1. A method of transmitting matrix-surround encoded audio signal over a low bitrate connection, the method comprising:

receiving matrix-surround encoded source audio;

separating the source audio into a frequency spectrum having a plurality of discrete audio frequencies;

identifying a cutoff threshold to distinguish which of the plurality of audio frequencies are to be encoded using a first matrix-surround preserving encoding method and which of the plurality of audio frequencies are to be encoded using a second non matrix-surround preserving encoding method;

encoding a first set of the plurality of audio frequencies below the cutoff threshold using the first matrix-surround preserving audio encoding method;

encoding a second set of the plurality of audio frequencies above the cutoff threshold using the second non matrix-surround preserving audio encoding method; and

streaming the first and second sets of encoded audio to a decoder via one or more modem connections.

2. The method of claim 1, wherein the first matrix-surround preserving encoding method comprises a selected one of a “

dual-mono”

encoding method and an “

MS coding”

encoding method.

3. The method of claim 1, further comprising:

identifying an upper bound within the frequency spectrum to determine an audio bandwidth of the transmitted audio signal.

4. The method of claim 3, wherein the audio bandwidth varies proportionally as the identified cutoff threshold varies.

5. The method of claim 1, wherein the first and second sets of encoded audio are streamed to a decoder via one or more analog modem connections.

6. A method of encoding matrix-surround encoded audio for transmission over a low bitrate connection, the method comprising:

identifying matrix-surround encoded source audio;

separating the source audio into a frequency spectrum having a plurality of discrete audio frequencies;

identifying a cutoff threshold;

encoding a first set of the plurality of audio frequencies below the cutoff threshold using a first matrix-surround preserving audio encoding method; and

encoding a second set of the plurality of audio frequencies above the cutoff threshold using a second non matrix-surround preserving audio encoding method.

7. The method of claim 6, further comprising:

transmitting the first and second sets of encoded audio to a client device over the low bitrate connection.

8. The method of claim 7, wherein the bitrate of the low bitrate connection falls within the range of 44 kbps-96 kbps.

9. The method of claim 7, wherein the bitrate of the low bitrate connection is less than 96 kbps.

10. The method of claim 7, wherein the first and second sets of encoded audio are transmitted to the client device in association with one or more descriptors to facilitate identification of the cutoff threshold by the client device.

11. The method of claim 7, wherein the first and second sets of encoded audio are streamed to a decoder via one or more analog modem connections.

12. The method of claim 6, wherein the cutoff threshold corresponds to a 7 KHz audio frequency.

13. The method of claim 6, wherein the first matrix-surround preserving encoding method comprises a selected one of a “

dual-mono”

encoding method and an “

MS coding”

encoding method.

14. The method of claim 6, further comprising:

identifying an upper bound within the frequency spectrum to determine an audio bandwidth of the transmitted audio signal.

15. The method of claim 14, wherein the audio bandwidth varies proportionally as the identified cutoff threshold varies.

16. In a client device, a method of decoding a matrix-surround encoded audio bit stream transmitted over a low bitrate connection, the method comprising:

receiving the bit stream;

decoding the bit stream into a frequency spectrum having a plurality of discrete audio frequencies;

determining a cutoff threshold used to encode the matrix-surround encoded audio signals;

decoding a first set of the plurality of audio frequencies below the determined cutoff threshold using a first matrix-surround preserving audio encoding method; and

decoding a second set of the plurality of audio frequencies above the cutoff threshold using a second non matrix-surround preserving audio encoding method.

17. The method of claim 16, wherein the bitrate of the low bitrate connection falls within the range of 44 kbps-96 kbps.

18. The method of claim 16, wherein the bitrate of the low bitrate connection is less than 96 kbps.

19. The method of claim 16, wherein the first and second sets of encoded audio are decoded by the client device based at least in part upon one or more descriptors transmitted in association with the matrix-surround encoded audio to facilitate identification of the cutoff threshold by the client device.

20. The method of claim 16, wherein the first and second sets of encoded audio are streamed to a decoder via one or more analog modem connections.

21. The method of claim 16, wherein the cutoff threshold corresponds to a 7 KHz audio frequency.

22. The method of claim 16, wherein the first matrix-surround preserving decoding method comprises a selected one of a “

dual-mono”

decoding method and an “

MS coding”

decoding method.

23. The method of claim 16, further comprising:

identifying an upper bound within the frequency spectrum to determine an audio bandwidth of the transmitted audio signal.

24. A recordable medium having instructions stored thereon, which when executed, implement a method for encoding matrix-surround encoded audio for transmission over a low bitrate connection comprising:

identifying matrix-surround encoded source audio;

separating the source audio into a frequency spectrum having a plurality of discrete audio frequencies;

identifying a cutoff threshold;

encoding a first set of the plurality of audio frequencies below the cutoff threshold using a first matrix-surround preserving audio encoding method; and

encoding a second set of the plurality of audio frequencies above the cutoff threshold using a second non matrix-surround preserving audio encoding method.

25. The recordable medium of claim 24, wherein the method further comprises:

transmitting the first and second sets of encoded audio to a client device over the low bitrate connection.

26. The recordable medium of claim 25, wherein the bitrate of the low bitrate connection falls within the range of 44 kbps-96 kbps.

27. The recordable medium of claim 25, wherein the bitrate of the low bitrate connection is less than 96 kbps.

28. The recordable medium of claim 25, wherein the first and second sets of encoded audio are transmitted to the client device in association with one or more descriptors to facilitate identification of the cutoff threshold by the client device.

29. The recordable medium of claim 24, wherein the first and second sets of encoded audio are streamed to a decoder via one or more analog modem connections.

30. The recordable medium of claim 24, wherein the cutoff threshold corresponds to a 7 KHz audio frequency.

31. The recordable medium of claim 24, wherein the first matrix-surround preserving encoding method comprises a selected one of a “

dual-mono”

encoding method and an “

MS coding”

encoding method.

32. The recordable medium of claim 24, wherein the method further comprises:

identifying an upper bound within the frequency spectrum to determine an audio bandwidth of the transmitted audio signal.

34. A recordable medium having instructions stored thereon, which when executed, implement a method for decoding matrix-surround encoded audio transmitted over a low bitrate connection comprising:

receiving matrix-surround encoded source audio;

separating the source audio into a frequency spectrum having a plurality of discrete audio frequencies;

determining a cutoff threshold used to encode the matrix-surround encoded audio signals;

decoding a first set of the plurality of audio frequencies below the determined cutoff threshold using a first matrix-surround preserving audio encoding method; and

decoding a second set of the plurality of audio frequencies above the cutoff threshold using a second non matrix-surround preserving audio encoding method.

33. The recordable medium of claim 35, wherein the audio bandwidth varies proportionally as the identified cutoff threshold varies.

35. The recordable medium of claim 34, wherein the bitrate of the low bitrate connection falls within the range of 44 kbps-96 kbps.

36. The recordable medium of claim 34, wherein the bitrate of the low bitrate connection is less than 96 kbps.

37. The recordable medium of claim 34, wherein the first and second sets of encoded audio are decoded based at least in part upon one or more descriptors received in association with the matrix-surround encoded audio to facilitate identification of the cutoff threshold.

38. The recordable medium of claim 34, wherein the first and second sets of encoded audio are streamed to a decoder via one or more analog modem connections.

39. The recordable medium of claim 34, wherein the cutoff threshold corresponds to a 7 KHz audio frequency.

40. The recordable medium of claim 34, wherein the first matrix-surround preserving decoding method comprises a selected one of a “

dual-mono”

decoding method and an “

MS coding”

decoding method.

41. The recordable medium of claim 34, wherein the method further comprises:

identifying an upper bound within the frequency spectrum to determine an audio bandwidth of the transmitted audio signal.

42. An apparatus comprising:

a processor to execute instructions;

a modem; and

a memory device communicatively coupled to the processor and modem and having stored thereon a plurality of instructions, which when executed, cause the apparatus to

receive matrix-surround encoded source audio via the modem;

separate the source audio into a frequency spectrum having a plurality of discrete audio frequencies;

determine a cutoff threshold used to encode the matrix-surround encoded audio signals;

decode a first set of the plurality of audio frequencies below the determined cutoff threshold using a first matrix-surround preserving audio encoding method; and

decode a second set of the plurality of audio frequencies above the cutoff threshold using a second non matrix-surround preserving audio encoding method.

43. The apparatus of claim 42, wherein the bitrate of the low bitrate connection falls within the range of 44 kbps-96 kbps.

44. The apparatus of claim 42, wherein the bitrate of the low bitrate connection is less than 96 kbps.

45. The apparatus of claim 42, wherein the first and second sets of encoded audio are decoded based at least in part upon one or more descriptors received in association with the matrix-surround encoded audio to facilitate identification of the cutoff threshold.

46. The apparatus of claim 42, wherein the cutoff threshold corresponds to a 7 KHz audio frequency.

47. The apparatus of claim 42, wherein the first matrix-surround preserving decoding method comprises a selected one of a “

dual-mono”

decoding method and an “

MS coding”

decoding method.

48. The apparatus of claim 42, wherein the method further comprises:

identifying an upper bound within the frequency spectrum to determine an audio bandwidth of the transmitted audio signal.

49. An apparatus comprising:

a receiver operative to receive matrix-surround encoded audio signals via a modem, separate the audio signals into a frequency spectrum having a plurality of discrete audio frequencies, and determine a cutoff threshold used to encode the matrix-surround encoded audio signals; and

a decoder operative to decode a first set of the plurality of audio frequencies below the determined cutoff threshold using a first matrix-surround preserving audio encoding method and decode a second set of the plurality of audio frequencies above the cutoff threshold using a second non matrix-surround preserving audio encoding method.

50. The apparatus of claim 49, wherein the receiver receives matrix-surround encoded audio signals via an analog modem over a low bit rate connection.

51. The apparatus of claim 49, wherein the cutoff threshold used to encode the matrix-surround encoded audio signals is determined by one or more descriptors received in association with the matrix-surround encoded audio signals.