The MOTM 120 Suboctave Multiplexer is a cool module for audio processing. I've found a way to use it for control voltage generation too. I DC-coupled the main output so it works with all input frequencies. LFO inputs can produce a 16-step sequence for controlling a VCO pitch, all adjustable with the internal mixer. I used the extra panel space to add five new outputs. There is a pulse output for each of the four suboctaves. These outputs are +/-5V for invertibility. I can use them to gate envelopes at different stages in the sequence. The fifth output is a fixed-level weighted mix of the four suboctaves, range 0 to about +6V. This produces a staircase wave of 16 equal steps when only the A input is used. The cross-product with the B input can produce very interesting patterns. All the new outputs have audio frequency application, as well. This is a simple circuit with just three TL072 op amps (though it does entail a bunch of wiring).
Why would I do this? Well, I am one of those oddballs who does not intend to use a keyboard controller. I am in search of patches that do interesting semi-random things. So I am after sources of stepped voltage to generate pitch sequences, when I am in the mood for "notes". In this same vein, I am planning to build one of Ken Stone's Infinite Melody modules, enhanced with an internal clock and noise source. If you're a DIY type, you should check out Cat Girl Synth.
One day, after I get the full MOTM module complement together and start discovering what it can do, I might just enter one of those "aleatoric" composition contests.
-Richard Brewster
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