Digital DIY synths? Somewhat diverging

[Harvey Devoe Thornburg]

> 
> Digital methodology other than DSP can also be employed.  Such as Walsh
> Function Generators.  I believe that someone else on this list has
> experimented with Walsh. 

Walsh is kind of a DSP technique, just not a linear one.
You can do nonlinear filtering with Walsh functions
as well as function generation.

Some time ago I experimented with the Walsh-Hadamard transform
for image processing, which projects the image onto a set of
Walsh functions rather than the standard Fourier (sine wave)
basis.  If you do a "lowpass filter" in the Walsh domain this
is the same as averaging blocks, which produces "blocky" images like 
when you don't want to show someone's face on TV.  Of course
this can be done just be averaging blocks, but other kinds of
filters (like bandpass) don't have so obvious results.  Because
of the implicit downsampling and stairstep interpolation, the 
Walsh lowpass has a lot of aliasing/imaging but they could be
useful for a variety of noise and percussion sounds. 
 
The cool thing about the Walsh-Hadamard transform is that 
it is all done with addition and subtraction, and it obeys 
a FFT recursion.  So it turns out to be fast and more suited
to real-time.

--Harvey

> have also mixed analog with digital for hybrid systems.  Some things
> are very simple using digital, such as frequency division (flip flop
> divide down) and multiplication (PLL at least).
> 
> -- Scott Gravenhorst
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>