[sdiy] Synthesizers...

[David G. Dixon]

Scott,

Thanks for that.  It makes me feel even more inclined to leave it in the
circuit.  Not a bad little addition for $1.25!

David G. Dixon
Professor
Department of Materials Engineering
University of British Columbia
309-6350 Stores Road
Vancouver, B.C. V6T 1Z4
Canada
 
Tel 1-604-822-3679
Fax 1-604-822-3619
 
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> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
> bounces at dropmix.xs4all.nl] On Behalf Of Scott Nordlund
> Sent: Wednesday, February 18, 2009 11:19 AM
> To: synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] Synthesizers...
> 
> 
> 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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