came across an interesting article in comp.dsp
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by [EMAIL PROTECTED]
subject: fast mdct
If you only want MDCT's of small, fixed sizes, you might look at the code
generator in FFTW (http://theory.lcs.mit.edu/~fftw). It can automatically
derive and generate hard-coded, efficient MDCT/DCT/MDST/DST transforms of
any small size. (These are currently somewhat experimental, and wehaven't
built a framework for general sizes yet.)For example, the MDCT of size 18 in
the Lame source requires 18*18=324multiplications and 17*18=306 additions. The
one FFTW generates requires46 multiplications and 91 additions (or a few less
multiplications, if youinclude a factor of 0.5 in the normalization).
If you need general length MDCTs, you might check out FFTPACK (from
www.netlib.org), which computes the MDCT using a real FFT of the same
length, plus some twiddling.
Cordially,Steven G. Johnson
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I had a quick look at the gensrc stuff in fftw but couldn't make head or tail
of it.
*shrug*
more speed
later
mike
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