[sdiy] Low Pass Gate passing DC - forgedabouydit

John L Marshall john.l.marshall at gte.net
Tue Jun 25 15:48:12 CEST 2002

There should be an integrator following the full wave rectifier. The
tradeoff is to choose an intrgrator that is fast enough to track dynamic
transients yet still filter out low frequency ripple. If the integrator is
voltage controlled then it can accomodate a variety of situations.

Take care,
----- Original Message -----
From: "mark verbos" <a0284520 at addcom.de>
To: "synth DIY" <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, June 25, 2002 4:57 AM
Subject: Re: [sdiy] Low Pass Gate passing DC - forgedabouydit

> The Buchla 230 envelope follower is NOT a vactrol circuit. It is more or
> less just a full wave rectifier. There are extra controls to make the
> decay time and the pulse output section.
> check it out here. http://home.swipnet.se/cfmd/synths/companies/buchla/
> mark
> Peter Grenader wrote:
> >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
> >DC level through a Buchla low pass gate circuit, it just cocks it's ear
> >you like a dog and does nothing.
> >
> >I was hoping to replicate (foolish me) that famous (in my world anyway)
> >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
> >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
> >at the beginning of the attack.
> >
> >No use arguing how he did it, I dropped him a note a couple of days ago
> >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
> >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
> >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
> >sweet spot
> >
> >But ooooooh-nooooooo, this circuit deosn't respond to contant DC levels
> >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
> >oblidged.
> >
> >let me know and thanks,
> >
> >Peter
> >
> >
> >
> >
> >

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