[sdiy] Synthesizers...

[Tom Wiltshire]

I really recommend the link John posted about this stuff. An  
excellent read:

	http://www.soundonsound.com/sos/Mar03/articles/synthsecrets47.asp

Antti is dead right too, but it took me a little while to see what  
he's on about.

	pwm(phase) = saw(phase) - saw(phase + pw)

	detuned saw	= saw(phase) + saw(phase + pw)
  			        = 2*saw(phase) - saw(phase) + saw(phase + pw)
      				= 2*saw(phase) - pwm(phase)

Maths scare me these days (wasn't always so) but this is an elegant  
way to express it.

T.


On 18 Feb 2009, at 19:19, 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.
>
> 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?
>
> _________________________________________________________________
> Get more out of the Web. Learn 10 hidden secrets of Windows Live.
> http://windowslive.com/connect/post/jamiethomson.spaces.live.com- 
> Blog-cns!550F681DAD532637!5295.entry?ocid=TXT_TAGLM_WL_domore_092008
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>