Patent ID: 7822617

Claim:
In an encoder arranged to encode a multi-channel audio signal, said encoder including a first main encoder, a second auxiliary encoder and a controller, a method of encoding said multi-channel audio signal, comprising: encoding, using said first main encoder, a first signal representation of at least one of said multiple channels in a first main encoding process; and encoding, using said second auxiliary encoder, a second signal representation of at least one of said multiple channels in a second, filter-based auxiliary encoding process, characterized by: selecting, using said controller, for said second, filter-based auxiliary encoding process, a combination of i) frame division configuration of an overall encoding frame into a set of sub-frames, and ii) filter length for each sub-frame, according to a predetermined criterion, wherein said set of sub-frames includes sub-frames having different sizes and the filter length, for each sub frame, is selected in dependence on the length of the sub-frame; and encoding, using said second auxiliary encoder, for said overall frame, said second signal representation in each of the sub-frames of the selected set of sub-frames in accordance with the selected combination; and generating, using said controller, output data representative of the selected frame division configuration and filter length for each sub-frame of the selected frame division configuration, wherein said output data includes data that while indicating the selected frame division configuration of an encoding frame into said set of sub-frames at the same time provides an indication of the selected filter length for each sub-frame.