10.6

Table Of Contents
710Logic Pro Instruments
Filters
Filters overview
The purpose of the filter in a subtractive synthesizer is to remove portions of the signal—
the frequency spectrum—sent from the oscillators. After filtering, a brilliant-sounding
sawtooth wave can become a smooth, warm sound without sharp treble.
The filter sections of most subtractive synthesizers contain two primary controls known
as cutoff frequency—often abbreviated to cutoff—and resonance. Other common filter
parameters are drive and slope. The filter section of most synthesizers can be modulated
by envelopes, LFOs, the keyboard, or other controls such as the modulation wheel. See
Modulation overview.
Basic filter types
There are several basic filter types. Each has a different effect on various portions of the
frequency spectrum.
Highpass filter: High frequencies are passed; low frequencies are attenuated.
Lowpass filter: Low frequencies are passed; high frequencies are attenuated.
Bandpass filter: Only frequencies within a frequency band are passed.
Band reject filter: Only frequencies within a frequency band are attenuated. This filter
type is also known as a notch filter.
Allpass filter: All frequencies in the spectrum are passed, but the phase of the output is
modified.
Cutoff frequency
The cutoff frequency, or cutoff, determines where the signal is cut off. Simpler
synthesizers have only lowpass filters. If a signal contains frequencies that range from 20
to 4000Hz and the cutoff frequency is set at 2500Hz, frequencies above 2500Hz are
filtered. The lowpass filter allows frequencies below the cutoff point of 2500Hz to pass
through unaffected.