Backward-compatible integration of harmonic transposer for high frequency reconstruction of audio signals

A decoder for decoding an encoded audio bitstream, the decoder comprising:

• an input interface for receiving the encoded audio bitstream, the encoded audio bitstream including audio data representing a lowband portion of an audio signal;
• a core decoder for decoding the audio data to generate a decoded lowband audio signal;
• a deformatter for extracting from the encoded audio bitstream high frequency reconstruction metadata, the high frequency reconstruction metadata including operating parameters for a high frequency reconstruction process that linearly translates a consecutive number of subbands from a lowband portion of the audio signal to a highband portion of the audio signal;
• an analysis filterbank for filtering the decoded lowband audio signal to generate a filtered lowband audio signal;
• a deformatter for extracting from the encoded audio bitstream a flag indicating whether either linear translation or harmonic transposition is to be performed on the audio data;
• a high frequency regenerator for regenerating a highband portion of the audio signal using the filtered lowband audio signal and the high frequency reconstruction metadata in accordance with the flag;
• and
• a synthesis filterbank for combining the filtered lowband audio signal and the regenerated highband portion to form a wideband audio signal.