[sdiy] Low Pass Gate passing DC - forgedabouydit
petergrenader at mksound.com
Tue Jun 25 06:01:19 CEST 2002
Hark, the possiblity of yet another string on this already over-cooked
subject (me being the primary chef involved):
But i thought you guys would like to know that if you try and gate a contant
DC level through a Buchla low pass gate circuit, it just cocks it's ear at
you like a dog and does nothing.
I was hoping to replicate (foolish me) that famous (in my world anyway) Mort
Subotnick percussive slap used on Until Spring and Sky of CS. He did it
using a control track which was fed through a Buchla Envelope Follower
(which i believe is vactrol based) which was not only trigger the envelope,
but creating the frequency transcient as well. The EF was set to a very
fast decay which was going through a voltage processor and processed to
barely make a tiny upward frequency spike to the sounding oscillator right
at the beginning of the attack.
No use arguing how he did it, I dropped him a note a couple of days ago and
this is straight from the butterfly's mouth, so to speak.
Why i suspect the B Env Follower to be vactrol based is if you listen to
those trancients he created, they are very breathy. I assumed this was due
to a vactrol's slow response awakening to the control track bleep. It
created a timing thing that gave you barely a hint of the transcient.
So, since I don't have a Buchla Envelope follower, I figured I could get the
same result if I used a trigger as the control signal in my Low Pass Gate
clones, gating a pot-variable constant DC level. By gating a constant
level, I figured I'd be able to adjust it until I would hit the timbral
But ooooooh-nooooooo, this circuit deosn't respond to contant DC levels at
it's input (makes sense since-in the intrument for which is was designed
there was no way of getting that DC to the gate signal input anyway).
If anyone knows if the Buchla Ebnvelope Follwer used a vactrol, I'd be much
let me know and thanks,
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