> OK, except the Doepfer one already mentioned. Sorry, shot too quick on
> that one... I spend a lot more time on the SDIY forums and lists than
> here, so making it yourself is always my first response ;-)
>
> The Doepfer one seems like it should do what the Buchla ones did,
> but of
> course Buchla sprinkled a lot of extra magic in his designs...
>
> best,
> D.
>
> Derek Holzer wrote:
> > What you are looking for is a low pass gate filter:
> >
> > http://www.buchla.com/historical/b200/292-lopassgate.html
> >
> > There are several DIY implementations of this filter/gate, but no
> > commercially available ones. Grab that soldering iron!
> >

... or this one http://www.makenoisemusic.com/QMMG.html (which has
more features than most other units, like high pass mode though the
mode change with gates on the Doepfer is unique)

...or currently non-eurorack one from Cyndustries and Buchla has his
current 292e. He retains the strategy (also followed by Plan B who of
course is influenced by Don) of not including a hardwired feedback path.

In passing I'll add that the the Doepfer mode change with gate input
feature seems to lend itself to being sequenced. There is a Buchla
292C schematic on the web showing a 70s module with switchable modes
meant for computer control, I'd guess those plans were studied for
the Doepfer module. The current Buchla 292e as with most parameters
on every module can have it's settings stored and recalled from memory.

About the exact sound. Firstly the youtube video seems to have some
reverb on it. Though the charm of the lowpass gate is due to the
vactrol and it's lag which leaves a little decay on a very short
sound. Likely the backhanded comments about the ease of Buchla's
sounding like a banjo or DX7 xylophone. Basically a short duration
sound with dense harmonics quickly followed by a dampened decay with
increasingly fewer harmonics.

If you look at the simpler Buchla VCOs like the 258, which influenced
the Plan B Model 15 and is being cloned this year by Mark Verbos in
Buchla 200 format, it's worth noticing that there is a VC waveshape
control going from a Saw or a Square to a Sine on simpler Buchla
VCOs. The significance is clearly some Buchla sounds you'll hear have
their harmonics diminishing as output by the VCO, not just coming
from the Lowpass Gate. Additionally Buchla VCOs are often either in a
pair on one module with FM inputs or a "Complex Oscillator"
containing a dedicated second modulation OSC generating FM more or
less by default. So my point here is on Buchla based VCO designs have
options to adjust harmonics on the VCO rather than a more typical
unchanging waveshape outs. Also, as synthesists working with FM know,
a high index level will often produce very dense sidebands that
approach but are different from standard noise. One use is in hard
attack transients, so while I'm not sure of the exact quality the
person posting wants I'm thinking it might very well be partly the
source going into the LPG not so much the particular brand's design
of LPG, though the designs out there sound different.

It's been commented that even building with the same kind of
vactrol, two lowpass gates will sound and behave slightly
differently. Mainly in that the same setting will have a different
time length which would be apparent in the behavior of shorter
settings. Not the most critical factor but worth noting

Since Buchla typically included 4 lowpass gate units on a module,
users were encouraged to use more than one, so 2 in series was a
typical option. That would further cut the "leakage" from the gate
fully closed if it's audible and not wanted or allow a patched
adjustable feedback path.

> the doepfer is unusual because its a single unit and the others are
> all dual or quad. I wonder if that is a problem, also I wonder how
> essential a gate delay, or dual gate delay is for ths kind of sound
> - I have an AS single gate delay at the moment

The term "gate" can be misleading to some degree. I know I was
confused when I first encountered it. It's basically a VCA and a 12db
LPF controlled from the same source with the ability to select either
or both. They behave differently enough to sound unique from a VCA
and VCF pair of more "typical" modules.

You would not be applying a gate to them, rather an envelope. But you
are onto something discussing gate delay. Typically on a Buchla, at
least one unit on a Quad Function Generator would be patched to the
lowpass gate. The Buchla 281 or similar is an ASR generator that is
close but not exactly like Doepfer's a143-1. The Doepfer has some
additional features but notably lacks a sustain. The a143-2 does have
sustain but lacks VC attack and decay. All these modules have a
cascade sort of ability where you can trigger the start of a second
generator when the first gets to a specific point. Doepfer has
options to adjust the point. Buchla just uses the end of the attack.
Buchla adds an OR-ing mixer for pairs of generators rather than
Doepfer's mix out of all 4 generators on the a143-1. So one would
often be using 2 or more EGs (delays quite possible) and or multiple
LPGs to create more complex sounds. But I don't think that's the
secret of what people are hearing, I think it's the FM wave going
into the LPG

nick