Vibrato from PWM

[Tony Allgood]

Hi all,

I was playing about with my VCO modules today. I had this idea. Listening to
the pulse width being modulated by a sine LFO, you hear a FM type modulation
as well as the phase shifting pulse width stuff. Now this is good, but I
thought that if I fed the output PWM waveform into a flip-flop (divide by
2), I could get pitch shifting sound but without the pulse width changing.
Remember, the flip-flop will only change its output when a falling edge is
detected. It is therefore good for producing square waves. In fact what you
get is a very good vibrato effect without actually modulating the VCO's
pitch.

Of course you could use several comparators each with its own LFO to get
lots of different PWM outs. Pass each into a set of flip-flops, and you
would get a sound like multiple detuned VCOs. And no problem with frequency
tracking, because you are only using one VCO. I'm going to try this
sometime.

The frequency sweep range is not great and the heard pitch change is the
differential of the modulating CV... no square wave (two tone) vibrato
allowed. But for thickening up a solitary VCO without phasing its great.

Regards,

Tony Allgood, Cumbria, UK

e-mail: oakley at enterprise.net

Rack mounted Moog VCF module. Details to be found at...

http://aupe.phys.andrews.edu/diy_archive/schematics/effects/filter.html