Sawtooth oddities

[Matthew S. Padden]

Hi..

>
>I've got this weird problem with my semi-modular synth. If I use two slightly 
>detuned
>VCOs on sawtooth, then the final audio output appears to be very unstable. 
>For about
>a second or so, the sound is the usual rich phasing type sound, then 
suddenly >the sound 
>changes as though one osc. has sync'd with the other. In fact, the output 
>sounds rather
>nasty. When using triangle or square outputs, or any combination, this 
>sync'ing feeling
>just does not happen.
>
>If I modulate one of the VCOs with a LFO then the problem never occurs. 
>Probably because
>the oscilators need to have a fixed frequency to lock.
>
>The VCOs are CEM types and only share the same psu. The outputs are totally 
>isolated from
>one another until summed in the output mixer.
>

Is this anything to do with chaotic oscillation? In that, two oscillating 
systems 'near' to each other and oscillating at very similar frequencies will 
tend to achieve sync by themselves over a period of time. There are stories of 
a shelf full of cuckoo clocks, the pendulums of which were all swinging in 
perfect unison after a few weeks.

I mean 'near' in a relative sense; in this case, the PSU cabling will provide 
a link between the oscillators. Maybe try moving the power routing to the 
modules?

Strange that it only does it with sawtooth waves though...
--
Matthew S. Padden
Computer Music Research Group
Room M2/08, Music Dept.
Huddersfield University
Queensgate
Huddersfield
England HD1 3DH
p: +44 1484 422288 x2402
f: +44 1484 472656
e: mattp at mindless.com
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