[sdiy] Synthesizers...

[Grant Richter]

With all due respect:

Consideration needs to given to when you use the signals for gate  
sources in LFO mode.

Saw derived PWM moves only the rear edge of the "gate" signal and  
sounds correct rhythmically when moving from legato to staccato  
articulation.

Triangle derived PWM moves both the front and rear edge timing. This  
very hard to tap your foot to.

Also a secondary module clocked from the gate signal will expect to  
update the output value on the raising edge of the input. For  
example, a sequencer will advance to the new note value on the  
raising edge of the clock signal. This sounds fine with saw derived  
PWM but gets "stranger" when the front edge is changing in time from  
a tri derived pulse.
On Feb 18, 2009, at 3:12 PM, Ian Fritz wrote:

> At 12:19 PM 2/18/2009, Scott Nordlund wrote:
>
>> 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.
>
>
> Well, that's been discussed here at least a couple of times  
> before.  The Saw-based PWM is much stronger sounding than the Tri- 
> based effect, because it is more "phasey".  My original DPWG works  
> off of a Tri and has a more subtle sound than a similar unit I have  
> that works off of a Saw.  It is just a personal preference thing as  
> to which one sounds "better".  They're just different, that's all.
>
> Ian
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