Audio Compression

• US 20090271204A1
• Filed: 11/04/2005
• Published: 10/29/2009
• Est. Priority Date: 11/04/2005
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Tammi, Mikko
• Granted Patent: US 8,326,638 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/0208 Subband vocoders

Abstract

For audio encoding and decoding, in order to enhance coded audio signals, the audio signal is divided into at least a low frequency band and a high frequency band, the high frequency band is divided into at least two high frequency sub-band signals, and parameters are generated that refer at least to the low frequency band signal sections which match best with high-frequency sub-band signals.

Claims

1. Method for encoding audio signals with

receiving an input audio signal,

dividing the audio signal into at least a low frequency band and a high frequency band,

dividing the high frequency band into at least two high frequency sub-band signals,

determining within the low frequency band signal sections which match best with high-frequency sub-band signals, and

generating parameters that refer at least to the low frequency band signal sections which match best with high-frequency sub-band signals.

2. Method of claim 1, wherein generating parameters further comprises generating at least one scaling factor for scaling the low frequency band signal sections.

3. Method of claim 2, wherein the scaling factor is generated such that an envelope of the low frequency signal sections being transposed into the high-frequency sub-band signals using the parameters follows an envelope of the high frequency sub-band signal of the received signal.

4. Method of claim 2, wherein generating scaling factors comprises generating scaling factors in the linear domain to match at least amplitude peaks in the spectrum.

5. Method of claim 2, wherein generating scaling factors comprises generating scaling factors in the logarithmic domain to match at least energy and/or shape of the spectrum.

6. Method of claim 1, wherein generating parameters comprises generating links to low frequency signal sections which represent the corresponding high frequency sub-band signals.

7. Method of claim 1, wherein determining within the low frequency band signal sections which match best with high-frequency sub-band signals comprises using at least one of

A) normalized correlation,

B) Euclidian distance.

8. Method of claim 1, wherein at least samples of the low frequency signal sections are generated using modified discrete cosine transformation.

9. Method of claim 1, further comprising normalizing the envelope of the high frequency sub-band signals.

10. Method of claim 2, further comprising quantizing samples of the low frequency signal and quantizing at least the scaling factors.

11. Method of claim 1, wherein the input signal is divided into temporally successive frames, and further comprising detecting tonal sections within two successive frames within the input signal.

12. Method of claim 11, wherein detecting tonal sections comprises using Shifted Discrete Fourier Transformation.

13. Method of claim 11, further comprising adding sinusoids to tonal sections.

14. Method of claim 11, further comprising increasing the number of high frequency sub-bands for tonal sections.

15. Method for decoding audio signals with

receiving an encoded bit stream,

decoding from the bit stream at least a low frequency signal and at least parameters referring to low frequency signal sections,

utilizing samples of the low frequency signal and the parameters referring to the low frequency signal sections for reconstructing at least two high-frequency sub-band signals, and

outputting an output signal comprising at least the low frequency signal at least two high-frequency sub-band signals.

16. Encoder for encoding audio signals comprising

a receiver arranged for receiving an input audio signal,

a filtering element for dividing the audio signal into at least a low frequency band and a high frequency band, and further arranged for dividing the high frequency band into at least two high frequency sub-band signals, and

a coding element for generating parameters that refer at least to low frequency band signal sections which match best with the high-frequency sub-band signals.

17. Encoder of claim 16, wherein the coding element is arranged for generating at least one scaling factor for scaling the low frequency band signal sections.

18. Encoder of claim 16, wherein the coding element is arranged for generating the scaling factor such that an envelope of the low frequency signal sections being transposed into high-frequency sub-band signals using the parameters follows an envelope of the high frequency sub-band signals of the received signal.

19. Encoder of claim 16, wherein the filtering element is arranged for dividing the input signal into temporally successive frames, and for detecting tonal sections within two successive frames within the input signal.

20. Encoder of claim 19, wherein the filtering element is arranged for detecting tonal sections using Shifted Discrete Fourier Transformation.

21. Encoder of claim 19, wherein the coding element is arranged for adding sinusoids to tonal sections.

22. Encoder of claim 19, wherein the coding element is arranged for increasing the number of high frequency sub-bands for tonal sections.

23. Decoder for decoding audio signals comprising

a receiver arranged for receiving an encoded bit stream,

a decoding element arranged for decoding from the bit stream at least a low frequency signal and at least parameters referring to low frequency signal sections,

a generation element arranged for utilizing samples of the low frequency signal and the parameters referring to the low frequency signal sections for reconstructing at least two high-frequency sub-band signals.

24. System for digital audio compression comprising a decoder comprising

a receiver arranged for receiving an encoded bit stream,

a decoding element arranged for decoding from the bit stream at least a low frequency signal and at least parameters referring to low frequency signal sections,

a generation element arranged for utilizing samples of the low frequency signal and the parameters referring to the low frequency signal sections for reconstructing at least two high-frequency sub-band signals, and, an encoder comprising

a receiver arranged for receiving an input audio signal,

a filtering element for dividing the audio signal into at least a low frequency band and a high frequency band, and further arranged for dividing the high frequency band into at least two high frequency sub-band signals, and

a coding element for generating parameters that refer at least to low frequency band signal sections which match best with the high-frequency sub-band signals.

25. Computer readable medium having a computer program stored thereon for encoding audio signals, the program comprising instructions operable to cause a processor to

receive an input audio signal,

divide the audio signal into at least a low frequency band and a high frequency band,

divide the high frequency band into at least two high frequency sub-band signals, and

generate parameters that refer at least to low frequency band signal sections which match best with high-frequency sub-band signals.

26. Computer readable medium of claim 25, operable to cause a processor to divide the input signal into temporally successive frames, and to detect tonal sections within two successive frames within the input signal.

27. Computer readable medium of claim 26, operable to cause a processor to use Shifted Discrete Fourier Transformation for detecting tonal sections.

28. Computer readable medium of claim 26, operable to cause a processor to increase the number of high frequency sub-bands for tonal sections.

29. Computer readable medium having a program stored thereon for decoding bit streams, the program comprising instructions operable to cause a processor to

receive an encoded bit stream,

decode from the bit stream at least a low frequency signal and at least parameters referring to low frequency signal sections,

utilize samples of the low frequency signal and the parameters referring to the low frequency signal sections for reconstructing at least two high-frequency sub-band signals, and

put out an output signal comprising at least the low frequency signal and at least two high-frequency sub-band signals.