Filters are used to cut, boost, and pass audio signal frequency ranges.
Filters are an essential component within a synthesizer and they lay down the foundation for the most common form of synthesis, known as subtractive synthesis.
The filter cut-off is the driving force behind filters, this main filter control is used to determine which frequencies are cut-off and which frequencies stay (these frequencies could be in between, outside, above or below the cut-off point).
Various filter types are available in synthesizers and most of them are self-explanatory, the two basic filters are low and high. Low-Pass Filters allow all of the frequencies below the cut-off point through. High-Pass Filters do the opposite and let all frequencies above the cut-off through.
Bandpass Filters are used to let frequencies through that are within a determined band range. Band Notch filters do the opposite by stopping a specific band of frequencies from passing through, but allowing through the frequencies above and below that band.
Filters also come with a feature known as Resonance, this boosts the cut-off frequency that the filter is currently set to. The set frequency increases as it is given more boost, which eventually results in the filter self-oscillating, from which you’ll start to produce some unique sounds.