STEREOPHONIC AUDIO CODER AND DECODER

Claims

1. A method for decoding an encoded audio bitstream, comprising the steps of: extracting from the encoded audio bitstream a first waveform-encoded signal consisting of first spectral coefficients corresponding to frequencies up to a first crossover frequency for a first period of time; extracting from the encoded audio bitstream a second waveform-coded signal consisting of second spectral coefficients corresponding to a subset of frequencies above said first crossover frequency for said first period of time, wherein the second waveform-coded signal does not contain second spectral coefficients corresponding to frequencies up to the first crossover frequency for the first period of time; extract recovery parameters from the encoded audio bitstream; determine, on the basis of the second spectral coefficients, that the second form-coded signal has a specific format; and performing frequency reconstruction based on said specific format to expand a subset of frequencies above a second crossover frequency to generate an expanded signal for a first period of time, wherein the second crossover frequency is above the first crossover frequency, wherein the frequency reconstruction uses said reconstruction parameters, and wherein the reconstruction parameters comprise a spectral envelope of said subset of frequencies above said second crossover frequency.

2. The method of claim 1, wherein the first waveform-coded signal and the second waveform-coded signal share a common bit reservoir using a psychoacoustic model.

3. The method according to claim 1, wherein the first waveform-coded signal and the second waveform-coded signal are signals representing the waveform of the audio signal in the frequency domain.

4. A non-transitory computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform the method of claim 1.

5. An audio decoder for decoding an encoded audio bitstream, the audio decoder comprising: a first demultiplexer for extracting from the encoded audio bitstream a first waveform-encoded signal consisting of first spectral coefficients corresponding to frequencies up to a first crossover frequency for a first period of time; and a second demultiplexer for extracting from the encoded audio bit stream a second waveform-coded signal consisting of second spectral coefficients corresponding to a subset of frequencies above said first crossover frequency for said first period of time, wherein the second waveform-coded signal does not contain second spectral coefficients corresponding to frequencies up to the first crossover frequency for the first period of time; a frequency reconstructor for determining, based on the second spectral coefficients, that the second waveform-coded signal has a specific format, and for performing frequency reconstruction based on said specific format for expanding a subset of frequencies above the second crossover frequency to generate an expanded signal for the first period of time, wherein the second crossover frequency is above the first crossover frequency, wherein the frequency reconstruction uses reconstruction parameters extracted from the encoded audio bitstream, wherein these reconstruction parameters comprise a spectral envelope of said subset of frequencies above said second crossover frequency.