Before you can filter anything, you’ll need a sound source. Check out the VCO section for more information.
Anyway. Let’s take that boring A440 test tone and make it more interesting. Filters can be used to change the color of a sound, to take the sharp edges off or add harmonics to a dull one. Voltage Control (sending a current to the thing) can make it evolve. In a way, you can see it as a controllable limited equalizer. Limited in the sense that you can only change the Cut-Off (warm/dull) and Resonance (sharp) and maybe some extra gadgets like Gain and FM.
There are many filters available, but the Moog filter has become legendary. Other filters that are worth mentioning all have something to do with the pioneers of electronic music. You should definitely check out Sequential/Dave Smith because the Prophet filters are legendary too. If you’re looking for something more modern (even though it’s vintage), you should also take a look at the Z-Plane filter from Rossum Electro-Music. It’s the filter that made the Morpheus famous. Imagine you could use three filters and animate them in a 3D cube. Personally I chose the Mutable Instrument Ripples, but I am looking for something stereo and more spectacular.
Filters are really important for live performances. People can listen for hours to people who just play the CutOff and Resonance. Without a filter, your sound will be limited on expression and storytelling. If you run a stereo rig like me, order two – but they don’t have to be identical.
Look, no hands
With conventional synths you can use a Low Frequency Oscillator (LFO) or ADSR Envelope to change the shape of the filter movement. So in the next section we’re going to explore functions and methods we can use to shape the VCO and the VCF.