Convention Paper
Linear Filtering in MDCT Domain
AES Convention 124 · Paper 7340 · May 2008
Abstract
In this paper, expressions for convolution multiplication
properties of MDCT are derived starting from the equivalent DFT
representations. Using these expressions, methods for
implementing linear filtering through block convolution in
the MDCT domain are presented. The implementation is exact for
symmetric filters and approximate for non-symmetric filters
in the case of rectangular window based MDCT. For a general MDCT window
function, the filtering is done on the windowed segments and
hence the convolution is approximate for symmetric as well as non-symmetric
filters. This approximation error is shown to be perceptually
insignificant for symmetric impulse response filters.
Moreover, the inherent $50 \%$ overlap between adjacent
frames used in MDCT computation does reduce this approximation error similar
to smoothing of other block processing errors. The presented
techniques are useful for compressed domain processing of
audio signals.
