[sdiy] Dumb PWM question

[Tom Wiltshire]

Here's a sketch of a way to do it, at least for arbitary oscillator  
waveforms, if not arbitrary signals:

	http://www.electricdruid.com/images/pd/idea.gif

  It depends on the fact that there is a source of modulation that is  
synchronised with (in this case 'identical to') the input signal.
There is a delay line to provide the necessary storage. As someone  
pointed out, unless you delay the signal you'd have to look into the  
future. The circuit itself is basically a simple BBD vibrato  
modulated at audio frequencies.

Here's another picture of what the effect looks like:

	http://www.electricdruid.com/images/lfo/PDDiagramV9C.gif

Regards,
Tom


On 26 Feb 2008, at 17:55, jbv wrote:

>
>
> Tom Wiltshire a *crit :
>
>> I've done this with digital oscillator waveforms (generalised phase
>> distortion, of which PWM is a special case), but I can't see how
>> you'd do it without sampling, since it is effectively a time
>> distortion, and that's going to require some stored waveform.
>> I suppose the sampling could be done in the analogue domain (magnetic
>> tape?) with the PWM applied as a modulation to tape speed at the
>> input frequency.
>> It'd be a LOT easier on a DSP though....
>
> that's exactly what I thought... actually it's time compression for  
> 1 half
> of
> the period and time expansion for the other half...
>
> JB
>
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