Audio processing method and apparatus

A method of creating a compressed audio output signal from a plurality of different input audio signals, each including a plurality of channels, the method comprising:

• a) for each of said input audio signals, precomputing a transform corresponding to a desired compression format of said output audio signal;
• b) for each of said input audio signals, precomputing ancillary information relating to the compression of the transformed output audio;
• c) mixing together said transformed input signals in the transform domain to produce an output transform domain signal;
• d) algorithmically combining together said precomputed ancillary information to determine a suitable decompression strategy;
• and
• e) outputting compressed audio data comprising said output transform domain signal and said combined ancillary information,
• wherein said ancillary information includes at least one of the set consisting of:
• bit allocation information,
• suggested exponent strategies in the case the decompression includes exponent strategies,
• audio signal statistics to determine when to change strategy,
• information providing an indication of future bit allocation demand,
• frequency banded information for determining how mixing will effect masking in the case the compression uses masking, and
• in the case an input audio signal is divided into frames of data, the remaining bit allocation in a frame and a suggested average bit allocation for data within the frame.

A method of creating a compressed audio output signal from a plurality of different input audio signals, each including one or more audio channels, the method comprising:

• a) mixing together representations in the transform domain of a plurality of input signals, the mixing in the transform domain to produce an a representation of the output signal, each transform domain representation precomputed for a corresponding one of the plurality of different input audio signals;
• b) algorithmically combining together auxiliary information related to each input signal whose representations are mixed in the mixing step, the algorithmic combining to determine a suitable decompression strategy;
• and
• c) outputting compressed audio data comprising said output transform domain signal and said combined auxiliary information,
• wherein the plurality of representations of the input signals in the transform domain are obtained by, for each of the input signals whose representations are mixed, precomputing a transform corresponding to a desired compression format of said output audio signal,
• wherein the auxiliary information of each of the input signals whose representations are mixed is obtained by precomputing the auxiliary information related to the desired compression format, the auxiliary information including one or more precomputing steps of the set of precomputing steps consisting of:
• precomputing bit allocation information,
• precomputing suggested exponent strategies in the case the decompression includes exponent strategies,
• precomputing audio signal statistics to determine when to change strategy,
• precomputing information providing at any point in time an indication of future bit allocation demand, the information precomputing using future audio information,
• precomputing frequency banded information to provide for determining how mixing will effect masking and compression in the case the compression uses masking, and
• in the case an input audio signal is divided into frames of data, precomputing for a frame the remaining bit allocation space in the frame and the suggested average bit allocations for data within the frame.