Sunday, 21 November 2010

Patch Tips #14 - Sub-Harmonic Division

Using Maths or the VCS to generate sub-harmonic variation.

Today's Patch Tip is cribbed from Seth Nemec's Bananalogue/ Serge VCS demos and the 'Undertone Generator' patch in Rich Gold's Serge book:

"Sub-Harmonic Generator: If a series of triggers are applied to the VCS faster than the total rise and fall times, the module will divide the incoming signal by a whole number. In the audio range the output will be the sub-harmonic series."

The VCS has the benefit of an AC-coupled output, but I feel Maths offers finer control over the settings. As this patch relies on the rise time, Math's EOR pulse can be used to provide an even beefier sub signal.

The technique simply involves patching a mult of your principal oscillator to Maths' trigger input and mixing either the envelope or EOR with the main VCO in a filter etc. Set the response to linear, fall to fully CCW and then gradually increase the rise time. Additionally altering the fall time will give you more control over the timing and hence sub-divisions.

Here's what it can sound like: subharmonix.mp3

The patch relies on the envelope's inability to respond to a second trigger until it has completed its cycle, meaning it will 'skip' pulses and thus generate a lower frequency. You can try this patch with other trigger-able envelopes like the Plan B Model 10, Cwejman CTG-VC or Doepfer A-143-1, bearing in mind that the minimum possible cycle time and trigger response will affect the possible sub-divisions.

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