High frequency regeneration of an audio signal with synthetic sinusoid addition

1. A method performed in an audio decoder for reconstructing an original audio signal having a lowband portion and a highband portion, the method comprising:

receiving an encoded audio signal, the encoded audio signal including spectral coefficients of the lowband portion and not the highband portion;

extracting reconstruction parameters from the encoded audio signal, the reconstruction parameters including a cross over frequency, spectral envelope information, and location information, wherein the spectral envelope information includes a spectral envelope value for each frequency band of the highband portion and the location information specifies a particular frequency band of the highband portion;

decoding the encoded audio signal with a core audio decoder to obtain a decoded lowband portion, the core audio decoder operating at a first sampling frequency;

regenerating the highband portion based at least in part on the cross over frequency and the decoded lowband portion to obtain a regenerated highband portion, wherein the regenerating operates at a second sampling frequency that is twice the first sampling frequency;

creating a synthetic sinusoid with a level based at least in part on the spectral envelope value for the particular frequency band and a noise floor value for the particular frequency band, the synthetic sinusoid representing a tonal component;

adding the synthetic sinusoid to the regenerated highband portion in the particular frequency band specified by the location information, wherein the location information specifies a frequency band where a difference is detected between a highband of the original audio signal and the regenerated highband portion, and

combining the lowband portion and the regenerated highband portion to obtain a full bandwidth audio signal; and

outputting the full bandwidth audio signal,

wherein the audio decoder is implemented at least in part with hardware.

2. The method of claim 1 wherein the sinusoid is added to a middle of the particular frequency band.

3. The method of claim 1 further comprising adjusting the level of the particular frequency band to compensate for the synthetic sinusoid.

4. The method of claim 1 wherein the noise floor value represents a ratio between an energy of noise to be added to the particular frequency band and a total energy of the particular frequency band.

5. The method of claim 1 wherein the spectral envelope value is a scalefactor representing an averaged energy of the original signal over the particular frequency band.

6. The method of claim 1 further comprising adjusting a spectral envelope of the highband portion based on the spectral envelope information.

7. The method of claim 1 wherein the cross over frequency varies dynamically.

8. The method of claim 1 wherein the regenerating further comprising analyzing the decoded lowband portion to create a plurality of subband signals.

9. The method of claim 8 wherein the analyzing is performed by an analysis Quadrature Mirror Filter (QMF) bank.

10. The method of claim 1 wherein the combining is performed by a synthesis Quadrature Mirror Filter (QMF) bank.

11. The method of claim 1 wherein the noise floor value is used to adaptively add noise to the regenerated highband portion.

12. The method of claim 1 wherein the lowband portion and the highband portion are contiguous but not overlapping frequency regions.

13. The method of claim 1 wherein the regenerating includes transposing a number of adjacent subband signals from the lowband portion to the highband portion.

14. The method of claim 1 wherein the lowband portion includes audio content at or below the cross over frequency and the highband portion includes audio content at or above the cross over frequency.

15. The method of claim 1 further comprising dividing the highband portion into frequency bands, each frequency band representing a group of one or more consecutive Quadrature Mirror Filter (QMF) frequency band.

16. The method of claim 1 wherein the adding is performed in an envelope adjustment unit.

17. An audio decoder for reconstructing an original audio signal having a lowband portion and a highband portion, the audio decoder comprising:

an input interface for receiving an encoded audio signal, the encoded audio signal including spectral coefficients of the lowband portion and not the highband portion;

a demultiplexer for extracting reconstruction parameters from the encoded audio signal, the reconstruction parameters including a cross over frequency and spectral envelope information, the spectral envelope information including a spectral envelope value for each frequency band of the highband portion;

a core audio decoder for decoding the encoded audio signal to obtain a decoded lowband portion, the core audio decoder operating at a first sampling frequency;

a high frequency regenerator for regenerating the highband portion based on the reconstruction parameters and the decoded lowband portion to obtain a regenerated highband portion, wherein the high frequency regenerator operates at a second sampling frequency and the first sampling frequency is half the second sampling frequency;

a demultiplexer for extracting location information from the encoded audio signal, the location information specifying a particular frequency band of the highband portion;

an adder for adding a synthetic sinusoid to the regenerated highband portion in the particular frequency band specified by the location information, wherein the level of the sinusoid is based at least in part on the spectral envelope value for the particular frequency band and a noise floor value for the particular frequency band, wherein the location information specifies a frequency band where a difference is detected between a highband of the original audio signal and the regenerated highband portion, the, synthetic sinusoid representing a tonal component; and

a synthesizer for combining the lowband portion and the regenerated highband portion to obtain a full bandwidth audio signal; and

outputting the full audio signal,

wherein the audio decoder is implemented at least in part with hardware.