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Appendix B Synthesizer Basics 482
Filters
Filters overview
The purpose of the lter in a subtractive synthesizer is to remove portions of the signal—the
frequency spectrum—sent from the oscillators. After being ltered, a brilliant-sounding sawtooth
wave can become a smooth, warm sound without sharp treble.
The lter sections of most subtractive synthesizers contain two primary controls known as cuto
frequency—often abbreviated to cuto—and resonance. Other common lter parameters are
drive and slope. The lter section of most synthesizers can be modulated by envelopes, LFOs, the
keyboard, or other controls such as the modulation wheel.
Filter types
There are several lter types. Each has a dierent eect on various portions of the frequency
spectrum:
Highpass Band Reject Lowpass
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Highpass lter: High frequencies are passed; low frequencies are attenuated.
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Lowpass lter: Low frequencies are passed; high frequencies are attenuated.
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Bandpass lter: Only frequencies within a frequency band are passed.
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Band reject lter: Only frequencies within a frequency band are attenuated.
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Allpass lter: All frequencies in the spectrum are passed, but the phase of the output
is modied.