A filter filters out certain frequencies in the sound. There are four main types: a low-pass, high-pass, band-pass and notch, which are covered elseware in the glossary. Filters have two controls - the frequency control selects at which frequency the filter should start operating and the resonance control creates a peak just before the bit where it starts filtering out frequencies. This is used to create acid-type sounds....
AKS
This is one of the classic pieces in analogue synth history. Brian Eno still caries one
around and Klaus Schule Schulze still uses his on every recording. The pin-block
patching is a little strange at first, but the versatility is like that of a modular unit. You
can patch anything into anything and the built-in reverb, while a little cheezy, can be
anywhere in the signal chain.