Pseudo-Random CV/Optical Filtering
JC Maillet (c) 2006, 2008
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The "Ladder" S/H Filter (c) 2003
These are my three S/H filter design efforts. The first one (pictured below) consists of a Moog/Maestro/Oberheim sampler and oscillator section - with a triangle wave generator replacing the unreliable noise source ... The output of the CV circuit is then DC-shifted to accomodate an EMS ladder style LP Filter ... very cool behavior, with animated quasi-repetitive and staircase patterns ... unfortunately it didn't have enough filter depth for my taste, and was somewhat unpredictable for setting patterns - nice random tone generator though ... I should box it up ...
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The "Mother" Filter (c) 2005
The next one consists of keeping with the stock Moog/Maestro/Oberheim current-controlled filter and sampler block but this time it's all fed by a Roland MS-20 Ramp generator and a new Noise Generator/Mixer combo for producing Staircase, Random (straight S/H) and Staircase plus Random patterns - a nice success there ... the sampler block also allows for Glide function ... altogether monstrous, it includes a CV output and a scope probe socket for monitoring CV visually ... bypass is relay controlled ... this is also where I started experimenting with adding variable Gain and Offset controls to the Moog filter ...
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9-volt Optical Sample/Hold-Glide Filter (c) 2006
My third experiment was conceived, first because I wanted to test my linear opto-converter in another translator function ... second, I wanted to try yet a different filter, this time a light controlled multi-function State-Variable "Mutron III" filter (with High-Pass, Band-Pass and Low-Pass outputs) ... third, I wanted to see if I could make it all work under a single 9.6 vDC Boss/Ibanez power supply source ... and fourth, above all I wanted to see how/if opto-couplers could deal with sudden minute changes and be properly used as a control interface for a sharp sounding S/H effect ...
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The CV circuit is interfaced by a linear optical V-R converter whence two photo-cells are controlled in balanced unison to set the SV filter ranges ... this optical converter has an offset and gain adjustement as well, similar in function to my Moog filter mod, which results in the filter limits being set arbitrarily and precisely within a "desired" range of action ... [[ Note: in the Moog V-I converter how low the filter can go is fixed by the input bias voltage Vgs(DC) of the second device in the sampler channel - thus making it worth picking through several devices and choosing the one that gives good low-end range ]] ... aside from making the normal S/H sounds, when the State-Variable filter is traversing it's entire range at high speed it sounds like a hand saw blade warble, when it's doing the same in the lower range it can produce a percolating type sound ... the kind of depth/speed extremes I was hoping to find ...
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\\\ CLIP of Unit #3 ///
Tokai Love Rock >> Optical S/H >> Linear Compressor #1 >> Modded Fender Twin >> SM57 >> Korg D1600
Drums : Daniel Tremblay
The next version I'm working on will include a "triggered" function as part of the Control Voltage ramp generator ... it will be more like a Sweep-S/H-Glide filter, which can do precisely triggered ramps and mixed random ramps, plus have the Q control and the different filter options, including Notching ...
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