Spectral translation/folding in the subband domain
The present invention relates to a new method and apparatus for improvement of High Frequency Reconstruction (HFR) techniques using frequency translation or folding or a combination thereof. The proposed invention is applicable to audio source coding systems. This is accomplished by means of frequency translation in the frequency domain with spectral envelope adjustment in the same domain. The proposed invention offers a low-complexity HFR method useful in speech and natural audio coding applications.
1. A method for decoding an encoded signal to obtain an output audio signal that represents an original audio signal, wherein the method comprises:
receiving the encoded signal and obtaining therefrom envelope data and high-frequency reconstruction control signals;
processing the encoded signal to obtain low-frequency subband signals representing a low-frequency portion of the original audio signal;
copying subband signals in source area channels to higher-frequency channels in a reconstruction range specified by the high-frequency reconstruction control signals, wherein
a first source area channel having a frequency is copied to a first reconstruction range channel having a frequency that is higher than the first source area channel frequency,
a second source area channel having a frequency is copied to a second reconstruction range channel having a frequency that is higher than the second source area channel frequency,
the second source area channel frequency is higher than the first source area channel frequency, and
the second reconstruction range channel frequency is lower than the first reconstruction range channel frequency;
adapting the copied subband signals according to the envelope data; and
synthesizing the output audio signal from a combination of the low-frequency subband signals and the copied and adapted subband signals.
2. The method according to claim 1 that comprises decoding the encoded signal to obtain low-frequency subband signals in a plurality of source area channels.
3. An apparatus for decoding an encoded signal to obtain an output audio signal that represents an original audio signal, wherein the apparatus comprises:
a demultiplexor for receiving the encoded signal and obtaining therefrom envelope data and high-frequency reconstruction control signals;
an audio decoder for processing the encoded signal to obtain low-frequency subband signals representing a low-frequency portion of the original audio signal and for copying subband signals in source area channels to higher-frequency channels in a reconstruction range specified by the high-frequency reconstruction control signals, wherein
a first source area channel having a frequency is copied to a first reconstruction range channel having a frequency that is higher than the first source area channel frequency,
a second source area channel having a frequency is copied to a second reconstruction range channel having a frequency that is higher than the second source area channel frequency,
the second source area channel frequency is higher than the first source area channel frequency, and
the second reconstruction range channel frequency is lower than the first reconstruction range channel frequency;
an HFR envelope adjustment component for adapting the copied subband signals according to the envelope data; and
a synthesis filterbank for synthesizing the output audio signal from a combination of the low-frequency subband signals and the copied and adapted subband signals.
4. The apparatus according to claim 3 that decodes the encoded signal to obtain low-frequency subband signals in a plurality of source area channels.