Archive of the former Yahoo!Groups mailing list: MOTM

This filter is a klone of the Korg PS3100 synth's filter. It is also a klone
of the MAM filter box (made in Germany) which is a stereo version
(hence Dave stereo remark).

This filter (like the Moog filter in it's own way) is good for 1 sound, but
∗BOY∗ what a sound!

It makes the most W O N D E R F U L string and ambient pads you've ever
heard!!

The best demo I can offer is buy either "Equinox" or "Oxygene" by Jean
Michael Jarre.
The "swooshing" string sound is a Korg PS3100 (he also uses an old EH Small
Stone phaser)

The "smoothness" of the effect is because the filter is not really a
traditional VCF. Rather, it is
a filter that we "wiggle" the cutoff pots with a special device called a
Vactrol.

A Vactrol is a LED touching a cadmium-sulfide photocell. This resistance of
the photocell varies as the
LED intensity. The range of resistance is like 1K-100K. The Vactrol is the
size of a sugar cube.

Now, the "badness" of the photocell is that is is S L O W to react
to changes in the light from the LED.
This means the filter sorts of drags behind the LED, trying to play "catch
up". This effect causes the filters
to "slur" and "smear" when the control voltages changes slope. Like......the
peaks of a triangle wave.

It's sort of like pulling a toy car with a Slinky.

This "badness" of Vactrols is used in 95% of all audio compressors.
Including the $2300 Joe Meek box.

So, for $13 buy a JM Jarre CD and check it out! (plus, they are damn fine
CDs. I play them all the time)

Paul S.