Wasps, DCOs, OSCs and Bill Clintons pants?

[Don Tillman]

   Date: Fri, 30 Oct 1998 00:48:18 -0800 (PST)
   From: Don Tillman <don at till.com>

   And if your divide-by-N counter oscillator can't match the pitch
   accuracy of a 1940's Hammond Organ, what's the point?

Sorry, that was an obscure reference to a posting of mine on the
Hammond organ mailing list from roughly 5 years ago.

There had been a discussion comparing tonewheel technology to
top-octave-generator technology in organ designs.  They're both
simliar in that they both generate all the note frequencies off a
single source.  The TOG uses a divider for each note while the Hammond
uses the ratio of two gears, and since these gears will have an
integral number of teeth on them, it's effectively a ratio of two
integers.  So the Hammond theoretically can be more accurate.

Given the integers used in a TOG chip and the gear ratios used by
Hammond, I put together a little table and noticed that, sure enough,
the Hammond had about half the error as the TOG chip.  

I thought this was really interesting; that the "modern technology"
(at the time) of the TOG chip missed the standard set by the 1940's
Hammond.  Sure you could do an even more modern version today with
larger N's, but maybe a PLL frequency multiplier / divider for each
note would be a better approach.

So back to the original topic, for a divide-by-N based VCO, it's very
likely the context will be in a polyphonic synth, which is going to be
used to play chords, so I figure you'll want to be at least accurate
as a Hammond.

[I can find the old posting of mine if there's any interest.]

  -- Don