I just found out about a cool technique called self oscillation, which in short uses the resonance of a filter to create something close to a sine Wave. In this video I’m sharing how to set it up in Sylenth1 as well as some examples for how to use this technique.
How does a self oscillation work?
In oder to make any synth self oscillate you need some noise and a high pass or low pass filter. Since analog synthesisers have a noise floor produced by the electronic components the Synth is made of, there is always some noise running through the whole machine and therefore also the filters. In the digital world there are two approaches you can use. Your synth might be modeled after analog gear which means there is somewhat of a noise floor created by the plug-in. But you might be using a synth where that is not the case. In that case you can simply select one oscillator that create noise, and turn the gain almost all the way down. Sylenth1 is something in between these two options. It doesn’t have a noise floor in general, but supports self oscillation without using a noise oscillator.
How to set up the self oscillating filter
Noise somewhat contains energy at every frequency. If you use a filter it usually cuts some of those frequencies of at a certain point, the cutoff. But filters usually also have a resonance control, which allows you to boost the frequencies very close to the cutoff frequency. If you turn up the resonance all the way you will boost the frequency at the cutoff position by a lot. So it will stand out. If the Sound you’re applying the filter and resonance to, is a pretty quite noise sample, you will make the frequency at the cut off position stand out so much, that it creates something close to a sine wave.
How to use a self oscillating filter
Now that you have set up the self oscillating filter you can modulate the cutoff frequency in order to modulate the pitch of the sine wave. This works since by changing the cutoff you are changing the frequency that is being boosted by the resonance. Modulation the cutoff to move down will create lower notes and moving it up will create higher notes. if you press different keys on your keyboard it will always play the same note though. In order to use the Filter like a piano you will have to enable your keytracking all the way. This will make the filter cutoff follow the keyboard and produce higher and lower notes according the keys position. Last thing you have to do is tune the frequency according to your keyboard by using a spectrogram and positioning the filter cutoff so that it matched the pitch of the keyboard note you are playing.
Why use a self oscillating filter?
Back in the days many synthesisers didn’t have a sine wave to choose for it’s oscillators. So using a self oscillating filter was the best option to create something close to it. Now you can obviously just choose a sine wave, but using self oscillation create something cool. Instead of a perfect sine wave it creates some extra harmonics in a kind of special way. Using this can create amazing kick drums, 808 basses, keys, bells, plucks and many more.