The MDCT can be calculated using FFT. The naive approach, though, requires
a 2*n* length FFT for a length *n* block, because of the odd
transform. There are faster approaches though [10]. The MDCT can
be rewritten as an odd-time odd-frequency discrete Fourier transform
(O DFT)

[10] presents a fast algorithm for calculating

as

where

Thus, the MDCT can be calculated using only one *n*/4 point FFT and some
pre- and post-rotation of the sample points. The IMDCT can be calculated in
a similar way. See the code for a more detailed description.

Sat Mar 7 16:27:43 PST 1998