Split-band encoding and decoding of an audio signal

• US 20080208575A1
• Filed: 02/27/2007
• Published: 08/28/2008
• Est. Priority Date: 02/27/2007
• Status: Abandoned Application

• Current Assignee: Nokia Corporation
• Original Assignee: Nokia Corporation
• Inventors: Laaksonen, Lasse, Vasilache, Adriana, Ramo, Anssi
• Application Number:
  US11/712,214
• Publication Number:
  US 20080208575A1
• Time in Patent Office: Days
• US Class Current: 704/225
• CPC Class Codes: G10L 19/012 Comfort noise or silence coding
• CPC Class Codes: G10L 21/038 using band spreading techniques
• CPC Class Codes: G10L 25/18 the extracted parameters being spectral information of each sub-band

Abstract

For enabling an improved reconstruction of a high frequency band of an audio signal in a split-band coding approach, a value representative of a background noise level in an audio signal that is to be encoded is determined. Further, a gain value for the higher frequency band is determined. Further, a correction factor for the determined gain value is determined based on the determined value representative of the background noise level. The correction factor may be used at an encoding end for correcting the gain value before a corresponding codebook index is provided to a decoding end. Alternatively, the correction factor may be provided together with a codebook index for the gain value to a decoding end, and the decoding end may use the correction factor to correct the gain value if appropriate.

Claims

1. A method comprising:

determining a value representative of a background noise level in an audio signal that is to be encoded;

determining a gain value for a higher frequency band of at least two frequency bands of the audio signal; and

determining a correction factor for the determined gain value based on the determined value representative of the background noise level.

2. The method according to claim 1, wherein the determined gain value for the higher frequency band of the audio signal defines a desired relation between the energies of the audio signal and random noise, which is to be used to reconstruct the high frequency band of the audio signal when decoding the encoded audio signal.

3. The method according to claim 1, further comprising encoding a lower frequency band of the audio signal to obtain parameters enabling a reconstruction of the lower frequency band of the audio signal, wherein the determined gain value for the higher frequency band of the audio signal enables a reconstruction of the higher frequency band of the audio signal based on information obtained in the reconstruction of the low frequency band.

4. The method according to claim 1, wherein the correction factor is determined to be lower in the case of a determined value representing a higher background noise level in the audio signal and wherein the correction factor is determined to be higher in the case of a determined value representing a lower background noise level in the audio signal.

5. The method according to claim 1, wherein the correction factor for the determined gain value is determined based on the determined value representative of the background noise level in the audio signal and on a long term background noise level in the audio signal.

6. The method according to claim 1, further comprising determining a signal-to-noise ratio in the audio signal as the value representative of the background noise level in the audio signal.

7. The method according to claim 1, further comprising selecting a codebook index for the determined gain value for the higher frequency band of the audio signal and providing the codebook index together with the determined correction factor.

8. The method according to claim 1, further comprising correcting the determined gain value for the higher frequency band of the audio signal with the determined correction factor, selecting a codebook index for the corrected gain value and providing the selected codebook index.

22. A computer program product in which a program code is stored in a computer readable medium, said program code realizing the method of claim 1 when executed by a processor.

23. The computer program product according to claim 22, wherein the determined gain value for the higher frequency band of the audio signal defines a desired relation between the energies of the audio signal and random noise, which is to be used to reconstruct the high frequency band of the audio signal when decoding the encoded audio signal.

24. The computer program product according to claim 22, wherein said program code is further configured to encode a lower frequency band of the audio signal to obtain parameters enabling a reconstruction of the lower frequency band of the audio signal, wherein the determined gain value for the higher frequency band of the audio signal enables a reconstruction of the higher frequency band of the audio signal based on information obtained in the reconstruction of the low frequency band.

25. The computer program product according to claim 22, wherein the program code is configured to determine the correction factor to be lower in the case of a determined value representing a higher background noise level in the audio signal and to be higher in the case of a determined value representing a lower background noise level in the audio signal.

26. The computer program product according to claim 22, wherein the program code is configured to determine the correction factor for the determined gain value based on the determined value representative of the background noise level in the audio signal and on a long term background noise level in the audio signal.

27. The computer program product according to claim 22, wherein the program code is configured to determine a signal-to-noise ratio in the audio signal as the value representative of the background noise level in the audio signal.

28. The computer program product according to claim 22, wherein the program code is further configured to select a codebook index for the determined gain value for the higher frequency band of the audio signal and to provide the codebook index together with the determined correction factor.

29. The computer program product according to claim 22, wherein the program code is configured to correct the determined gain value for the higher frequency band of the audio signal with the determined correction factor, to select a codebook index for the corrected gain value and to provide the selected codebook index.

9. A method comprising:

determining a gain value for a higher frequency band of at least two frequency bands of an audio signal based on a received codebook index;

correcting the determined gain value based on a received correction factor for the gain value; and

reconstructing the higher frequency band of the audio signal based on the corrected gain value.

30. A computer program product in which a program code is stored in a computer readable medium, said program code realizing the method of claim 9 when executed by a processor.

10. An apparatus comprising:

a determination component configured to determine a value representative of a background noise level in an audio signal that is to be encoded;

a determination component configured to determine a gain value for a higher frequency band of at least two frequency bands of the audio signal; and

a determination component configured to determine a correction factor for the determined gain value based on the determined value representative of the background noise level.

11. The apparatus according to claim 10, wherein the determined gain value for the higher frequency band of the audio signal defines a desired relation between the energies of the audio signal and random noise, which is to be used to reconstruct the high frequency band of the audio signal when decoding the encoded audio signal.

12. The apparatus according to claim 10, further comprising a low-band encoding component configured to encode a lower frequency band of the audio signal to obtain parameters enabling a reconstruction of the lower frequency band of the audio signal, wherein the determined gain value for the higher frequency band of the audio signal enables a reconstruction of the higher frequency band of the audio signal based on information obtained in the reconstruction of the low frequency band.

13. The apparatus according to claim 10, wherein the determination component configured to determine a correction factor is configured to determine the correction factor to be lower in the case of a determined value representing a higher background noise level in the audio signal and to be higher in the case of a determined value representing a lower background noise level in the audio signal.

14. The apparatus according to claim 10, wherein the determination component configured to determine a correction factor is configured to determine the correction factor for the determined gain value based on the determined value representative of the background noise level in the audio signal and on a long term background noise level in the audio signal.

15. The apparatus according to claim 10, wherein the determination component configured to determine a value representative of a background noise level is configured to determine a signal-to-noise ratio in the audio signal as the value representative of the background noise level in the audio signal.

16. The apparatus according to claim 10, further comprising a selection component configured to select a codebook index for the determined gain value for the higher frequency band of the audio signal, wherein the selection component provides the codebook index and the component configured to determine a correction factor provides the determined correction factor.

17. The apparatus according to claim 10, further comprising a correction component configured to correct the determined gain value for the higher frequency band of the audio signal with the determined correction factor, and a selection component configured to select a codebook index for the corrected gain value and to provide the selected codebook index.

18. An electronic device comprising:

an apparatus according to claim 10; and

an audio signal interface.

21. A system comprising:

an apparatus according to claim 10; and

an apparatus comprising a decoding component configured to decode an audio signal encoded by the apparatus according to claim 10.

19. An apparatus comprising:

a determination component configured to determine a gain value for a higher frequency band of at least two frequency bands of an audio signal based on a received codebook index;

a correction component configured to correct the determined gain value based on a received correction factor for the gain value; and

a reconstruction component configured to reconstruct the higher frequency band of the audio signal based on the corrected gain value.

20. An electronic device comprising:

an apparatus according to claim 19; and

an audio signal interface.

31. An apparatus comprising:

means for determining a value representative of a background noise level in an audio signal that is to be encoded;

means for determining a gain value for a higher frequency band of at least two frequency bands of the audio signal; and

means for determining a correction factor for the determined gain value based on the determined value representative of the background noise level.

32. An apparatus comprising:

means for determining a gain value for a higher frequency band of at least two frequency bands of an audio signal based on a received codebook index;

means for correcting the determined gain value based on a received correction factor for the gain value; and

means for reconstructing the higher frequency band of the audio signal based on the corrected gain value.