MATRIXSYNTH: Doepfer A-101-1 Vactrol Filter: overview (LMS Eurorack Expansion Project)

Friday, December 29, 2017

Doepfer A-101-1 Vactrol Filter: overview (LMS Eurorack Expansion Project)

Published on Dec 29, 2017

"Also known as the 'Steiner' filter (as it’s an enhancement of a circuit Nile Steiner first published in 1974), this nice-sounding 2-pole multimode self-oscillating filter with vactrols on the cutoff and resonance inputs is unique in that it has a separate _input_ per filter mode, allowing the creation of alternate modes as well as frequency-dependent crossfades between multiple sources. The overview video breaks down like this:

0:00 some examples
0:41 circuit heritage
1:28 understanding vactrols
3:42 filter inputs, modes, and sweeps
7:30 resonance behavior
10:15 enveloping cutoff (including pinging the vactrol)
11:31 enveloping resonance (brass; percussion)

There is a second movie available that explores combining and fading between multiple inputs. It is included in the version of the Eurorack Expansion course on the Learning Modular website, and is being shared (along with additional notes) with my Patreon supporters.

The Learning Modular Patreon tribe:
The expanded version of the Eurorack Expansion course:"

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