Reconstructing an audio signal with a noise parameter
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 decoding the first part to obtain a decoded baseband audio signal. The method also includes extracting an estimated spectral envelope of the highband portion and a noise parameter from the second part and filtering the decoded baseband audio signal to obtain a plurality of subband signals. 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 adjusting a spectral envelope of the high-frequency reconstructed signal based on the estimated spectral envelope of the highband portion to obtain an envelope adjusted high-frequency 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;
obtaining a decoded baseband audio signal by decoding the first part, wherein the first part includes spectral components of the baseband portion and does not include spectral components of the highband portion, wherein the number of the spectral components of the baseband portion may vary dynamically;
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 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, wherein a frequency resolution of the estimated spectral envelope is adaptive;
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 ratio to an amplitude value.
6. The method of claim 1 further comprising limiting an 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 of implement the method of claim 1 .