High frequency regeneration of an audio signal with temporal shaping
A method for generating a reconstructed audio signal having a baseband portion and a highband portion is disclosed. The method includes deformatting an encoded audio signal into a first part and a second part and extracting, from the first part, temporal envelope information and spectral components of the baseband portion. The method further includes decoding the first part to obtain a decoded baseband audio signal. The decoding includes filtering in a frequency domain at least some of the spectral components of the baseband portion with the reconstruction filter using the temporal envelope information to shape a temporal envelope of the baseband portion. The method also includes extracting, from the second part, a noise parameter and an estimated spectral envelope of the highband portion and obtaining a plurality of subband signals by filtering the decoded baseband audio signal. The method further includes generating a high-frequency reconstructed signal by copying a number of consecutive subband signals of the plurality of subband signals and obtaining an envelope adjusted high-frequency signal by adjusting, based on the estimated spectral envelope of the highband portion, a spectral envelope of the high-frequency reconstructed signal.
1. A method for generating a reconstructed audio signal having a baseband portion and a highband portion, the method comprising:
deformatting an encoded audio signal into a first part and a second part;
extracting, from the first part, temporal envelope information, wherein the temporal envelope information includes coefficients representing a reconstruction filter;
extracting, from the first part, spectral components of the baseband portion, wherein the spectral components of the baseband portion do not include spectral components of the highband portion;
decoding the first part to obtain a decoded baseband audio signal, wherein the decoding includes filtering in a frequency domain at least some of the spectral components of the baseband portion with the reconstruction filter using the temporal envelope information to shape a temporal envelope of the baseband portion;
extracting, from the second part, a noise parameter and an estimated spectral envelope of the highband portion;
obtaining a plurality of subband signals by filtering the decoded baseband audio signal;
generating a high-frequency reconstructed signal by copying, in a circular manner, a number of consecutive subband signals of the plurality of subband signals;
obtaining an envelope adjusted high-frequency signal by adjusting, based on the estimated spectral envelope of the highband portion, a spectral envelope of the high-frequency reconstructed signal;
generating a noise component based on the noise parameter, wherein the noise parameter indicates a level of noise contained in the highband portion;
obtaining a combined high-frequency signal by adding the noise component to the envelope adjusted high-frequency signal; and
obtaining a time-domain reconstructed audio signal by combining the decoded baseband audio signal and the combined high-frequency signal;
wherein the method is implemented by an audio decoding device comprising one or more hardware elements.
2. The method of claim 1 wherein the plurality of subband signals is generated with one or more Quadrature Mirror Filters (QMF).
3. The method of claim 1 wherein the encoded audio signal is decoded using an inverse modified Discrete Cosine Transform (DCT).
4. The method of claim 1 wherein the noise parameter is represented in a form of a normalized ratio.
5. The method of claim 4 further comprising converting the normalized) to an amplitude value.
6. The method of claim 1 further comprising limiting amount of envelope adjustment of the high-frequency reconstructed signal.
7. The method of claim 6 further comprising compensating for the limiting by boosting the combined high-frequency signal.
8. The method of claim 1 further comprising smoothing, based on a parameter extracted from the encoded audio signal, an amount of envelope adjustment of the high-frequency reconstructed signal.
9. An audio decoding device comprising one or more hardware elements that implement the method of claim 1 by executing a sequence of instructions.
10. A non-transitory computer-readable medium containing instructions that when executed by an audio decoding device comprising one or more hardware elements, cause the audio decoding device to implement the method of claim 1 .
11. An audio decoder generating a reconstructed audio signal having a baseband portion and a highband portion, the audio decoder comprising:
a deformatter for extracting a first part and a second part from an encoded audio signal;
an extractor for obtaining, from the first part, temporal envelope information, wherein the temporal envelope information includes coefficients representing a reconstruction filter;
an extractor for obtaining, from the first part, spectral components of the baseband portion, wherein the spectral components of the baseband portion do not include spectral components of the highband portion;
a decoder for obtaining a decoded baseband audio signal from the first part, wherein the decoder includes a reconstruction filter for processing at least some of the spectral components of the baseband portion using the temporal envelope information to shape a temporal envelope of the baseband portion;
an extractor for obtaining, from the second part, a noise parameter and an estimated spectral envelope of the highband portion;
a filter for obtaining a plurality of subband signals from the decoded baseband audio signal;
a generator for creating a high-frequency reconstructed signal by copying, in a circular manner, a number of consecutive subband signals of the plurality of subband signals;
an envelope adjuster for obtaining an envelope adjusted high-frequency signal by adjusting, based on the estimated spectral envelope of the highband portion, a spectral envelope of the high-frequency reconstructed signal;
a noise generator for generating a noise component based on the noise parameter, wherein the noise parameter indicates a level of noise contained in the highband portion;
a combiner for obtaining a combined high-frequency signal by adding the noise component to the envelope adjusted high-frequency signal; and
a synthesizer for obtaining a time-domain reconstructed audio signal by combining the decoded baseband audio signal and the combined high-frequency signal;
wherein the audio decoder comprises one or more hardware elements.