Transform encoding/decoding of harmonic audio signals

1. A method of encoding a frequency transformed harmonic audio signal, comprising:

receiving the frequency transformed harmonic audio signal;

generating an encoded frequency transformed harmonic audio signal corresponding to the frequency transformed harmonic audio signal, based on:

locating spectral peaks in the frequency transformed harmonic audio signal that have magnitudes exceeding a predetermined frequency dependent threshold;

encoding peak regions including and surrounding the located spectral peaks;

encoding at least one low-frequency set of Modified Discrete Cosine Transform (MDCT) coefficients outside the peak regions and below a crossover frequency that depends on a number of bits used to encode the peak regions;

encoding a noise-floor gain of at least one high-frequency set of not yet encoded MDCT coefficients outside the peak regions; and

outputting the encoded frequency transformed harmonic audio signal.

2. The encoding method of claim 1 , wherein a peak region is encoded by:

encoding spectrum position and sign of a peak;

quantizing peak gain;

encoding the quantized peak gain;

scaling predetermined frequency bins surrounding the peak by the inverse of the quantized peak gain; and

shape encoding the scaled frequency bins.

3. The encoding method of claim 1 , wherein encoding a low-frequency set of MDCT coefficients includes encoding the low-frequency set based on a gain-shape encoding scheme.

4. The encoding method of claim 3 , wherein the gain-shape encoding scheme is based on scalar gain quantization and factorial pulse shape encoding.

5. The encoding method of claim 1 , comprising encoding a noise-floor gain for each of two high-frequency sets.

6. A method of audio signal reconstruction comprising:

receiving an encoded frequency transformed harmonic audio signal;

decoding the encoded frequency transformed harmonic audio signal and thereby obtaining a reconstructed frequency transformed harmonic audio signal, based on:

decoding spectral peak regions of the encoded frequency transformed harmonic audio signal, said spectral peak regions comprising spectral peaks having magnitudes exceeding a predetermined frequency dependent threshold;

decoding at least one low-frequency set of Modified Discrete Cosine Transform (MDCT) coefficients of the encoded frequency transformed harmonic audio signal;

distributing the MDCT coefficients of each low-frequency set outside the spectral peak regions and below a crossover frequency that depends on a number of bits used to encode the peak regions;

decoding a noise-floor gain of at least one high-frequency set of MDCT coefficients of the encoded frequency transformed harmonic audio signal that are outside of the spectral peak regions;

filling each high-frequency set of MDCT coefficients with noise having the corresponding decoded noise-floor gain; and

outputting the reconstructed frequency transform harmonic audio signal.

7. The reconstruction method of claim 6 , wherein a peak region is decoded by:

decoding spectrum position and sign of a peak;

decoding peak gain;

decoding a shape of predetermined frequency bins surrounding the peak; and

scaling the decoded shape by the decoded peak gain.

8. The reconstruction method of claim 6 , wherein decoding a low-frequency set includes decoding the low-frequency set based on a gain-shape decoding scheme.

9. The reconstruction method of claim 8 , wherein the gain-shape decoding scheme is based on scalar gain decoding and factorial pulse shape decoding.

10. The reconstruction method of claim 6 , comprising decoding a noise-floor gain for each of two high-frequency sets.

11. An encoder for encoding a frequency transformed harmonic audio signal, said encoder configured to obtain the frequency transformed harmonic audio signal and comprising a processing circuit configured to:

generate an encoded frequency transformed harmonic audio signal corresponding to the frequency transformed harmonic audio signal, based on being configured to:

locate spectral peaks in the frequency transformed harmonic audio signal that have magnitudes exceeding a predetermined frequency dependent threshold;

encode peak regions including and surrounding the located spectral peaks;

encode at least one low-frequency set of Modified Discrete Cosine Transform (MDCT) coefficients outside the peak regions and below a crossover frequency that depends on a number of bits used to encode the peak regions; and

encode a noise-floor gain of at least one high-frequency set of not yet encoded MDCT coefficients outside the peak regions; and

output the encoded frequency transformed harmonic audio signal.

12. The encoder of claim 11 , wherein the processing circuit is configured to:

encode a spectrum position and sign of a peak;

quantize peak gain and encode the quantized peak gain;

scale predetermined frequency bins surrounding the peak by the inverse of the quantized peak gain; and

shape encode the scaled frequency bins.

13. A user equipment (UE) comprising the encoder of claim 11 , said encoder configured to output the encoded frequency transformed harmonic audio signal to radio circuitry of the UE, for transmission to a remote receiver.

14. A decoder configured for audio signal reconstruction, said decoder configured to receive an encoded frequency transformed harmonic audio signal and comprising a processing circuit configured to:

decode the encoded frequency transformed harmonic audio signal and thereby obtain a reconstructed frequency transformed harmonic audio signal, based on being configured to:

decode spectral peak regions of the encoded frequency transformed harmonic audio signal, said spectral peak regions including spectral peaks having magnitudes exceeding a predetermined frequency dependent threshold;

decode at least one low-frequency set of Modified Discrete Cosine Transform (MDCT) coefficients;

distribute the MDCT coefficients of each low-frequency set outside the spectral peak regions and below a crossover frequency that depends on a number of bits used to encode the peak regions;

decode a noise-floor gain of at least one high-frequency set of MDCT coefficients outside of the spectral peak regions; and

fill each high-frequency set of MDCT coefficients with noise having the corresponding noise-floor gain; and

output the reconstructed frequency transformed harmonic audio signal.

15. The decoder of claim 14 , wherein the processing circuit is configured to:

decode spectrum position and sign of a peak;

decode peak gain;

decode a shape of predetermined frequency bins surrounding the peak; and

scale the decoded shape by the decoded peak gain.

16. A user equipment (UE) comprising the decoder of claim 14 , said decoder configured to output the reconstructed transformed harmonic audio signal to further audio signal processing circuitry of the UE, for generating a corresponding audio signal.