Backward-compatible integration of high frequency reconstruction techniques for audio signals

An audio processing unit for performing high frequency reconstruction of an audio signal, the audio processing unit comprising:

• an input interface for receiving an encoded audio bitstream, the encoded audio bitstream including audio data representing a lowband portion of the audio signal and high frequency reconstruction metadata;
• a core audio decoder for decoding the audio data to generate a decoded lowband audio signal;
• a deformatter for extracting from the encoded audio bitstream the high frequency reconstruction metadata, the high frequency reconstruction metadata including operating parameters for a high frequency reconstruction process, the operating parameters including a fill element with an identifier indicating a start of the fill element and fill data after the identifier, wherein the fill data includes a backward-compatible extension container including a patching mode parameter, wherein a first value of the patching mode parameter indicates spectral translation and a second value of the patching mode parameter indicates harmonic transposition by phase-vocoder frequency spreading, and wherein the identifier is a three bit unsigned integer transmitted most significant bit first and having a value of 0x6;
• an analysis filterbank for filtering the decoded lowband audio signal to generate a filtered lowband audio signal, wherein the filtering is performed by an analysis filterbank that includes analysis filters, hk(n), that are modulated versions of a prototype filter, p0(n), according to:
• h
• k
• (
• n
• )
• =
• p
• 0
• (
• n
• )
• ⁢
• exp
• ⁢
• {
• i
• ⁢
• π
• M
• ⁢
• (
• k
• +
• 1
• 2
• )
• ⁢
• (
• n
• -
• N
• 2
• )
• }
• ,
• 0
• ≤
• n
• ≤
• N
• ;
• 0
• ≤
• k
• <
• M
• where p0(n) is a real-valued symmetric or asymmetric prototype filter, M is a number of channels in the analysis filterbank and N is an order of the prototype filter, wherein the prototype filter, p0(n), is derived from coefficients of Table 4 herein;
• and
• a high frequency regenerator for reconstructing a highband portion of the audio signal using the filtered lowband audio signal and the high frequency reconstruction metadata, wherein the reconstructing includes a spectral translation if the patching mode parameter is the first value and the reconstructing includes harmonic transposition by phase-vocoder frequency spreading if the patching mode parameter is the second value.