[sdiy] Imperfect VCO

[Oakley Sound]

> To get something interesting you really have to draw large distortions
of the original curve...

But try this one. Alter the rise time vs fall time of a triangular
waveform. The difference between a 'sawtooth' with a rise time to fall
time ratio of 1:99 and 2:98 is very noticeable. I tried this with the
Ion, and was suprised how 'digital' the 0:100 setting was and how much
warmer the 2:98 setting was. I was hearing [I think] the fundamental
becoming stronger. Perhaps a significant part of the 'tone' of the
sawtooth output on VCOs could be controlled by the reset time. But
thinking about it, is it that we describe a powerful VCO by the strength
of the fundamental? A perfect sawtooth being that little bit too bright?

I should do some basic fourier maths on sawtooth waveforms with
differing flyback times.

Also there is quite a difference in tone when there is a discontinuity
in the falling ramp of the sawtooth. When setting up Polyfusion VCOs
[triangle based core], you need to adjust the symmetry of the waveshaper
to give you zero glitching on falling ramp. A small glitch as seen on
the scope does give a different tone.

Regards,

Tony Allgood                       Penrith, Cumbria, England

Oakley Sound Systems                   www.oakleysound.co.uk
Modular Synthesisers      www.oakleysound.co.uk/projects.htm