| Filter | |
| A filter is an electrical device which removes parts of the spectrum of a signal passed through it. An equalizer permits passage of the entire spectrum, with level changes to some frequency bands. |
| Filters usually act in a subtractive fashion and attenuate certain parts of the spectrum. Filters come in 5 types: low pass (high frequency attenuation), high pass (low frequency attenuation), band pass (atteneuates above and below a central portion), band reject (attenuates a central portion) & dip filters (very narrow band). |
| The compositional possibilities of filters are greatly increased when we consider modulating the parameters of the filter over time. (see low pass for sound example) |
| Filter parameters such as cut-off frequency, resonance, and amount of cut/boost are often controlled. | A simple low frequency oscillator (LFO) can be used or a more complex wave function defined and applied via MIDI or in software. | Filter parameters can be changed at relatively slow sub-audio rates or modulated at near-audio and audio frequencies. |