Interesting Paper available on Moog VCF

[Don Tillman]

   Date: Wed, 18 Sep 1996 13:22:19 -0400 (EDT)
   From: Eli Brandt <eli at ux3.sp.cs.cmu.edu>

   Don Tillman wrote:
   > Analog nonlinearities are extremely difficult to implement digitally.
   > When you add a digital nonlinearity you create an infinite number of
   > harmonics, and these alias around and sound pretty crappy.

   Interesting.  My gut feeling is that if the waveshaping function is
   "smooth" in some sense, it should produce a band-limited output.  

Only for a few special case curves.  Square-law f'rinstance.

But try an exponential curve.  That's pretty smooth, right?  Put a
single sinewave through an exponential transfer function and you've
got a waveform that contains *all* harmonics (the amount diminishes as
the harmonics get higher of course).  That makes for a lot of
aliasing.  But don't take my word for it, prove it yourself; work out
the Fourier series of expt(sin(wt)).

  -- Don