[sdiy] Synthesizers...

[Scott Nordlund]

I've never seen any synth-related reference to this (guess it would be
in electronotes if it's anywhere), but saw-derived PWM and tri-derived
PWM do have different spectra.  PWM from a sawtooth wave results in an
upward (or downward) sideband shift proportional to the modulation
frequency, while PWM from a triangle wave results in a simultaneous
upward and downward sideband shift.  This is why saw-derived PWM can
sound "out of tune", especially at low frequencies.  Using a triangle
wave should sound much better.  Unfortunately synths usually use the
saw wave for PWM, even when a triangle is available.

One of my professors in college had written a paper on it...

----------------------------------------
> Date: Tue, 17 Feb 2009 23:48:06 -0800
> From: dixon at interchange.ubc.ca
> Subject: RE: [sdiy] Synthesizers...
> To: tom at electricdruid.net; synth-diy at dropmix.xs4all.nl
> CC:
>
> I thought of one little innovation today which is very simple: I put in a
> switch to select between the triangle and the ramp for the input to the
> pulse wave comparator. When the resulting pulses are mixed with the sines
> or triangles from the same VCO, they morph them in different ways. I'm not
> sure if the results really sound very different, but it is a very simple
> thing to do, so I'll probably keep it. Has anyone else tried this?

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