Strange modulation schemes & animated lfo's

Paul Perry pfperry at melbpc.org.au
Thu Jun 26 09:24:38 CEST 1997


>>     John Atwood has this General Radio pink-noise generator from
>>     the 1950s. It uses a 6D4 thyratron surrounded by a big alnico
>>     permanent magnet. Apparently the field biases the ionized
>>     gas, producing substantial noise. It is sensitive to the
>>     magnetic pole placement versus the thyratron internal structure.
>>     A bizarre scheme, but it apparently works well.

I think this scheme is pretty well limited to thyratron or other gas
discharge devices....it probably works because the currents flowing through
the gas snake around because the magnetic field generates sideways movements
in the ions/electrons, making new paths.....
those 'imitation candle' neon discharge xmas kitch-0-rama bulbs give a bad
lfo effect too....this idea of cadmium ldr cells stuck to the front of a TV
was once described in the Journal of Experimental Musical
Instruments..someone built a box that sat on the tv and made it look a it
like an octopus with  corrugated arms coming down to suction cups with light
dependent resistors which you stuck to the screen...a rare case of a tv with
something decent on it...

seriously though, i have had very good results with three lfo's in a ring
configuration, the output of each going to the frequency control of the
next. i realized this with the voltage controlled lfo's from a roland system
100m, but the oscillators re absolutely non-critical, so long as they are
not square wave, also you have to set at least one fairly slow with respect
to the others....only drawback, if it is,  being that you can not possibly
get exactly the same effect twice.....i suspect that this config is the
minimum component assembly required to generated truly chaotic (as opposed
to random) low frequency oscillations.....GO FOR IT!

paul perry





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