New Wiard Module: Borg "Assimilator" Filters

[Grant Richter]

> This is the part I'm most curious about. I thought the Buchla
> was primarily a VCA, with the option to make the sound
> darker as well as more attenuated at the same time, the VCF
> function being just a resonance-less additional mode.

Buchla originally described the circuit as an "amplitude and
frequency domain modifier". The mode switch was originally
labeled "amplitude - frequency - both" and targeted at simulating
the psychoacoustic effects of approaching and receding sound
sources. The entire Buchla 200 is a quadraphonic system
designed for moving sound sources in quad space.

> Now your results hint in another direction: Fast enough for
> VCF but not for a general purpose VCA - did I get this right ?

Fast is relative. Serge VCAs are extremely fast - too fast for
my taste, you have to add attack time to each envelope to
get rid of the "click" which is not control voltage feedthru
but a discontinuous FFT. The slew rate limiting which is
"punchy" in the filter makes the VCAs seem "soft".

> Which Vactrols have you used (if I may ask),

You'll have to try different ones like I did ;^)

>and did you
> include Buchla's dynamic CV circuit (which supposedly
> speeds up the Vactrol response by "enhancing the edges"
> of the LED current) ?

Thats just a 1 uF cap that bypasses the current limiting
resistor in the LED circuit.

>I always wondered how well that
> part worked. I assume it can only speed up the response
> of the LDR to a very small degree, but Buchla did his best
> to squeeze the last bit of speed out of them. Does this
> make sense, or did I interpret it wrong ?
> 

Speed is also relative. While 3 decades in 5 milliseconds
doesn't seem too fast relative to an OTA, you don't normally
sweep a filter over it's full 10 octave range. The small signal response
is significantly faster than the large scale step response.

I'm also getting tired of targeting designs at Electronica and Techno
where people care how fast things are. There is a growing group
of users who are interested in getting a less synthetic sound
from the instrument, who want an electronic instrument with
the beauty and expressiveness of a cello. At which point, attack
time doesn't matter as much as tone color.