Reconstructing an audio signal having a baseband and high frequency components above the baseband
A method and system for reconstructing an original audio signal is disclosed. The original audio signal has a baseband up to a cutoff frequency and high-frequency components not included in the baseband above the cutoff frequency. The system includes a bitstream deformatter that extracts a representation of the baseband, an estimated spectral envelope, and noise-blending parameters from an audio bitstream. The system also includes a spectral component regenerator that copies or translates all or at least some of the baseband spectral components to non-overlapping frequency ranges of the high-frequency components not included in the baseband to generate regenerated spectral components. The system further includes a gain adjuster that modifies a spectral envelope of the regenerated spectral components based at least in part on the estimated spectral envelope and the noise-blending parameters to generate gain-adjusted regenerated spectral components.
1. An audio decoder for reconstructing an original audio signal having a baseband up to a cutoff frequency and high-frequency components not included in the baseband above the cutoff frequency, the audio decoder comprising:
a bitstream deformatter that extracts a representation of the baseband, an estimated spectral envelope, and noise-blending parameters from an audio bitstream, wherein the representation of the baseband is a frequency domain representation that includes baseband spectral components, and wherein the cutoff frequency is capable of being varied dynamically;
a spectral component regenerator that copies or translates all or at least some of the baseband spectral components to non-overlapping frequency ranges of the high-frequency components not included in the baseband to generate regenerated spectral components;
a gain adjuster that modifies a spectral envelope of the regenerated spectral components based at least in part on the estimated spectral envelope and the noise-blending parameters to generate gain-adjusted regenerated spectral components, wherein the noise-blending parameters include a noise parameter for each of a plurality of frequency bands above the cutoff frequency; and
a synthesis filterbank that:
combines a frequency domain representation of the baseband with the gain-adjusted regenerated spectral components to form a frequency-domain representation of a reconstructed audio signal, and
transforms the frequency-domain representation of the reconstructed audio signal into a time domain,
wherein the audio decoder comprises one or more hardware elements.
2. The audio decoder of claim 1 wherein the frequency domain representation of the baseband is generated with one or more Quadrature Mirror Filters (QMF).
3. The audio decoder of claim 1 wherein the noise parameter is represented in a form of a normalized ratio.
4. The audio decoder claim 3 further comprising converting the normalized ratio to an amplitude value.
5. The audio decoder of claim 1 further comprising a limiter that limits an amount of gain adjustment of the gain-adjusted regenerated spectral components.
6. The audio decoder of claim 5 further comprising a compensator that compensates for the limiter by boosting the gain-adjusted regenerated spectral components.
7. The audio decoder of claim 1 further comprising a smother that smooths, based on a parameter extracted from the audio bitstream, an amount of gain adjustment of the gain-adjusted regenerated spectral components.
8. The audio decoder of claim 1 wherein the one or more hardware elements include a memory, a processor, an integrated circuit or a programmable logic array.
9. A method for reconstructing an original audio signal having a baseband up to a cutoff frequency and high-frequency components not included in the baseband above the cutoff frequency, the method comprising:
extracting a representation of the baseband, an estimated spectral envelope, and noise-blending parameters from an audio bitstream, wherein the representation of the baseband is a frequency domain representation that includes baseband spectral components, and wherein the cutoff frequency is capable of being varied dynamically;
copying or translating all or at least some of the baseband spectral components to non-overlapping frequency ranges of the high-frequency components not included in the baseband to generate regenerated spectral components;
modifying a spectral envelope of the regenerated spectral components based at least in part on the estimated spectral envelope and the noise-blending parameters to generate gain-adjusted regenerated spectral components, wherein the noise-blending parameters include a noise parameter for each of a plurality of frequency bands above the cutoff frequency;
combining a frequency domain representation of the baseband with the gain-adjusted regenerated spectral components to form a frequency-domain representation of a reconstructed audio signal; and
transforming the frequency-domain representation of the reconstructed audio signal into a time domain,
wherein the method is implemented with one or more hardware elements.