>> Fourier would be proud. >> (SFT strikes again :-) ) > I'm not sure what your point is. Sorry! That wasn't meant to be a criticism. Just noting the "classic" approach as opposed to the 'throw an FFT at it' approach. A nice choice. > I'm assuming SFT is supposed to mean Slow Fourier Transform Yes. >, as apposed to FFT (Fast Fourier Transform)? =A0Do you see a > way to apply the FFT algorithm to checking for the existence of a few kno= wn > frequencies that aren't in a nice evenly spaced progression? Possibly yes, or one of the arcane variants of it - but that wasn't my aim. Hmm - deep memory or random firing neuron suggests Winograd transform. Gargoyles - nope - addition biased method. WikiP suggests Guo & Burns, Shentov and Edelman (Sparse and approximate) - and I'll happily admit to having heard of none of them before. Long long ago I played with optimising in place butterflies for use on VERY limited memory VERY slow processors (not my actual project) but nowadays I'd be as likely to accidentally end up with a Lorentz Butterfly as a Tukey one. Hours of fun - http://en.wikipedia.org/wiki/Fast_Fourier_transform Russell -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist