Filter Effects - What Are They, and How Are They Used?

Filter effects are designed to add emphasis and animation to instruments. By limiting the frequency range and varying the filter's frequency, filter effects can create focused, even vowel-like tones that add liquidity to rhythmic strumming and vocal qualities to lead parts. Like a tone knob on steroids, filter effects dramatically change the core tone of your instrument through a variety of different triggering approaches.

The Technology of Filter Effects

A filter works by allowing a range of frequencies pass through the filter, while removing the rest of the frequencies from your input signal. Filters used as an effect on guitars often offer multiple frequencies, such as a low-pass filter that passes only lower frequencies, a bandpass that pushes through the mid-frequencies, and a high-pass for only trebly highs. Precisely which frequencies are filtered out is determined by either manufacturer preset or via a user-definable cutoff. Most filters feature a resonance control, often labeled 'Q', that provides a boost at the selected cutoff.

Types of Filters

Wah Pedals

Wah pedals are treadle-rocked expression pedals where your foot moves the treadle to sweep the filter band frequency, which provides hands-free filter control. Jimi Hendrix, Kirk Hammett, and Joe Satriani are just a few players who have popularized the wah sound and cemented it in the guitar tone lexicon. The benefit to the wah format is complete control of how wide and fast the sweep happens.

Envelope Filters

Envelope filters turn control of the filter’s sweep over to an envelope circuit, which is sensitive to the attack of your playing through the dynamics of the signal it receives. Using a process of Attack, Sustain, Decay, and Release, the envelope sweeps the filter from a set starting point to as high a peak as the input signal dictates, and begins a decay and release (close) once the signal falls below a certain input. The result is a sound that is similar (or identical) to a wah, but with the filter entirely following the dynamics of your playing.

Modulated Filter

One of the rarer formats of filtering effects, modulated filters us an LFO (similar to a chorus or tremolo effect) to control the sweep of the filtering, resulting in a consistent waveform through which the band-frequency modulates. This is the least dynamic version of a filtering effect, as it responds to the LFO and not to playing or physical manipulation.

Sample/Hold Filters

Sample/Hold filters are probably the most exotic of filter effects, and are certainly the most synth-like. These effects work by randomly grabbing a frequency band, applying it for some duration (anywhere from 100ms to multiple seconds), jumping to another frequency band, and repeating. The result is a robotic hard step between frequency shifts that almost gives the impression of new notes getting played. The most famous use of this effect on guitar is probably Frank Zappa’s Ships Ahoy.

Examples of Filter Effects

Classic Wah Pedals- Vox V847, Dunlop 535Q Cry Baby, Fulltone Clyde Standard

Classic Envelope Filters- Mu-Tron III,  Seamoon Funk Machine, Ibanez AF-9, EHX Q-Tron

Classic Modulated Filter- Moog MF-101

Classic Sample/Hold Filters- Maestro Filter Sample/Hold, Xotic Robotalk, Zvex Ooh Wah

-HC-

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Chris Loeffler is a multi-instrumentalist and the Content Strategist of Harmony Central. In addition to his ten years experience as an online guitar merchandiser, marketing strategist, and community director he has worked as an international exporter, website consultant and brand manager. When he’s not working he can be found playing music, geeking out on guitar pedals and amps, and brewing tasty beer.