We tend instinctively to think of audio‑rate oscillators as sound‑generating circuits and low‑frequency oscillators (LFOs) as modulation circuits, as prescribed in the architecture of the vast majority of hard‑wired synthesizers. But, as we know, one of the simplest joys of the modular craft is repurposing even the most basic components of a conventional synthesizer voice to create something multidimensional and complex. Experimenting with an oscillator or two as audio‑rate modulation or trigger sources can at best yield some brilliant results, and at the very least encourage a new way of thinking about your patching.
One obvious example of this is FM synthesis, where the frequency of one ‘carrier’ oscillator is modulated at audio rate by one or more other oscillators to create a sound far more interesting than the sum of its parts (if you’re yet to explore creating FM voices with your oscillators, pause your reading here and we’ll probably see you tomorrow). There are a host of other potential destinations for our oscillators, though. Filter circuits respond excellently to audio‑rate modulation — often with more harmonically rich waveforms such as saw waves — and can lead to some wonderfully throaty, vocoder‑like sounds when the filter resonance is set just right (while we’re here, why not modulate that at audio‑rate too?).
If we take a sound module that expects gates, for example a drum or percussion module, we can squeeze some fascinating timbres out of it simply by triggering it very fast.
Pulse‑wave oscillators can be powerful tools for modulation or for generating ultra‑fast gates (since this is essentially what they are). If we take a sound module that expects gates, for example a drum or percussion module, we can squeeze some fascinating timbres out of it simply by triggering it very fast. I find it satisfying to tune a pulse‑wave VCO to a very low frequency so I can hear the module being ‘normally’ triggered, and then incrementally speed it up to hear exactly what it’s doing and tweak the sound as I go. Depending on how we’ve set the module’s voice, we could achieve anything from a harmonically complex pitched drone to a dense, atonal soundscape.
With any of the above, once we’ve found a sound that we like, we need to look at ways to make it into something useful. We can create variation with the simplest of gestures: sequencing or modulating the VCO’s frequency between low and high (often the more contrast the better) is a good place to start, while using a VCA or filter with an envelope to shape dynamics or frequency can also help to create musical playability. With our drum module, we could even make that envelope sharp enough to create a whole other percussive sound, totally repurposing our percussion module, in the name of percussion!
Next time you’re scratching your chin about modulation, trying an oscillator instead of an LFO might just be the trick. You may just bring out aspects of your system that you never knew existed.