Filter Pedals

A filter pedal changes your tone by controlling which frequencies of your instrument's signal get through and which get cut. Where an overdrive adds grit or a delay repeats what you played, a filter reshapes the frequency spectrum itself: roll off the highs and a bright guitar turns dark and muffled, sweep a narrow band up and down and you get the vocal "wah" sound every player recognizes, let the sweep follow your picking dynamics and you get the squelchy, funky envelope filter sound heard on countless funk and bass records.

The filter family is wide. At one end sit utility pedals that quietly trim harsh highs or muddy lows, like the Broughton Audio Low Pass Filter. At the other end are envelope filters that make your instrument quack, sweep and talk, like the Maestro Agena Envelope Filter and the Carl Martin Ottawa, and ring modulators that turn your signal metallic and otherworldly. This page explains what each kind does, how the circuits behave, what the knobs mean, and where a filter belongs in your signal chain.

What a filter pedal does to your sound

Every filter pedal is built around one idea: a cutoff point in the frequency spectrum. Frequencies on one side of that point pass; frequencies on the other side are reduced. Move the cutoff and the character of your tone moves with it. That single principle produces very different results depending on which direction the filter works and how the cutoff is moved.

A static filter, set once and left alone, works like a tone control with a sharper edge. Broughton Audio describes its Low Pass Filter pedal as a tool "for taming harsh high end such as fret buzz, string noise, and artifacts from other pedals," which is a practical use many players never associate with the word filter¹. Its High Pass Filter does the opposite job, which the maker calls "the perfect utility pedal for cleaning up the low end"².

A moving filter is where the effect becomes expressive. Sweep the cutoff and you hear the familiar wah motion. Let your own playing move it and it becomes an envelope filter. Aguilar describes the appeal of its Filter Twin, a dual-filter bass pedal, in terms of the sound two simultaneous sweeps produce:

Aguilar, maker product page³

Filters also show up inside other effects. Anasounds builds a "hum and noise filter inside the pedal" on its Savage and Utopia units, a power-supply cleanup measure rather than a tonal effect, which shows how broadly the word is used in pedal marketing⁴. On this page, a filter pedal means an effect whose main job is frequency shaping.

How a filter pedal works

Under the hood, a filter pedal is an amplifier circuit whose gain changes with frequency. The three building blocks that matter to a player are the cutoff, the slope and the resonance.

• Cutoff: the frequency where the filter starts working. Below or above it, depending on filter type, the signal passes largely untouched.
• Slope: how steeply frequencies beyond the cutoff are reduced. Sine Effect describes its L24 as "a steep low-pass filter pedal," meaning the highs drop off quickly rather than gradually⁵.
• Resonance (or peak): a boost at the cutoff point itself. High resonance makes the filter "ring" at its cutoff, which is what gives synth-style filters, such as the Manecolabs Saurus with its "analog resonant lowpass and bandpass synth filter," their vocal, honking character⁶.

What moves the cutoff separates one filter pedal from another. In a wah pedal you move it with your foot. In an envelope filter, a circuit called an envelope follower measures the level of your signal and translates it into control voltage: play harder, the filter opens. In an LFO-driven auto-filter, a low-frequency oscillator sweeps the cutoff up and down on a repeating cycle, like a slow, automatic wah. In a ring modulator, your signal is multiplied against an oscillator's frequency, which creates entirely new sum and difference frequencies rather than simply cutting existing ones.

For comparison, a chorus works nothing like this. As Lehle's Joki Schaller explains, "a chorus pedal basically works like a delay: it doubles the signal, but delays the copy for a few milliseconds, pitches it up and down a few cents and merges them back together"⁷. Chorus thickens; a filter subtracts and emphasizes.

Some designs let you drive the cutoff by hand. Behringer's flanger pedal includes a "manual mode to ride the integrated foot pedal directly across the filter," the same direct control a wah gives you⁸. And not every filter is a floor stompbox at all: Elta Music builds its Polivoks Filter and Polivoks Filter 2 for desktop use, "switched on with a switch, rather than a stomp button," aimed at players and synth users who tweak by hand rather than tap with a foot⁹¹⁰.

Envelope filters, auto-filters and ring modulators

These three categories cover most of what players mean by "filter pedal," and the boundaries between them are blurrier than the names suggest.

Envelope filters

An envelope filter reads your dynamics. The classic reference point is the Musitronics Mu-Tron III, and the design idea lives on in a long line of pedals. The FTelettronica Envelope Follower/Triggered Filter combines "envelope filter and triggered filter with static filter options" in one unit, meaning it can follow your attack, fire a one-shot sweep on a trigger, or hold a fixed setting¹¹. The Maestro Agena Envelope Filter is, in Gibson's words, "designed for ease of use," with a Sense knob setting the envelope's response to your picking¹². MOOER's Envelope packs the effect into what the maker calls "a pocket sized 'envelope filter'/'dynamic auto wah' pedal"¹³.

Envelope filters are a major category on bass. The MXR Bass Envelope Filter "delivers classic analog envelope filter sounds with separate Dry and Effect level controls," so the untouched low end can be blended back in alongside the filtered signal¹⁴. Aguilar's Filter Twin takes a different route, running two filter sweeps simultaneously for a more organic result³. Dreadbox describes its KINEMATIC as "an Envelope Filter effect pedal suitable for fretted instruments and synthesizers," a reminder that these circuits cross over into synth territory¹⁵.

Auto-filters and auto-wahs

An auto-wah produces the wah sound without your foot. Carl Martin describes the Ottawa plainly: "The Ottawa is an auto-wah / envelope filter pedal, essentially it gives you that funky wah-wah sound that follows your" playing¹⁶. Flamma's FC11 is likewise a "Pocket-sized envelope filter/dynamic auto wah pedal"¹⁷. The terms auto-wah and envelope filter are used almost interchangeably by makers, though some auto-filters, like the Maxon AF-9 Auto Filter, sweep on their own internal timing rather than your attack¹⁸¹⁹²⁰.

Ring modulators

A ring modulator is the extreme end of the family. Intensive Care Audio's VENA CAVA FILTER is "a distortion pedal with an auto-filter and ring modulation," stacking the metallic, atonal ring-mod sound on top of filtering and gain²¹. Champion Leccy's the Kilter V2 was designed as a utility modulation pedal but "also functions as a tremolo, a clean blend, parallel mixer or" ring modulator, showing how often ring modulation appears as one mode among several²².

Low-pass, high-pass and band-pass filters

Filter pedals are named for which frequencies they cut, and three types cover nearly everything.

Many pedals combine types. Alexander Pedals' Now We Are Ghosts includes a "resonant filter with low pass, high pass, band pass options," letting one pedal cover all three behaviors²³. Sine Effect's C24 "combines the two," high-pass and low-pass, "and also allows a clean boost of up to +20dB," with hand-matched components for consistency between the two filter stages²⁴. AMT Electronics builds Hi/Low pass filters plus a Presence control into its pedal preamps, applying fixed filtering as part of a bigger signal-shaping chain²⁵.

The synth-filter tradition is its own strand. The Moog MF-101 is a filter pedal in the Moog lineage²⁶, and Behringer's BM-11M is a "vintage-style analog low-pass filter pedal that delivers warm, resonant filtering" in the same lineage²⁷. PastFX's PX-101 Lowpass Filter continues the approach as a lowpass filter pedal²⁸, and Manecolabs' Saurus pedal pairs an analog resonant lowpass and bandpass synth filter in one unit²⁸⁶.

The usual controls: peak, sensitivity, range and volume

Filter pedals share a small set of knobs, and knowing what each does covers most of what you will meet.

Sensitivity deserves special attention because it is the control that makes an envelope filter track well or badly. MXR says "a simple twist of the Sensitivity knob can tailor the pedal for your attack, as well as adjust for passive or active basses," since active electronics deliver a hotter signal to the envelope detector¹⁴. Maestro's Agena puts the same function on its Sense knob, "the envelope's sensitivity and response to your picking attack"¹². The September Sound modded wah shows how far control sets can grow on filter-based pedals, adding high and low gain, clean blend, sensitivity and threshold, and frequency controls to a wah circuit²⁹.

Where a filter goes in the signal chain

Placement matters more with filters than with most effects, because a filter's behavior depends on the level and cleanliness of what feeds it.

BOSS's signal chain guidance puts wah and filter effects in a specific spot: "placing this filter effect directly after the tuner and before the drive section will optimize signal frequency before" the drive pedals shape it³⁰. The same guide puts the tuner first in the chain, before everything else³⁰.

The reasoning extends to any effect that tracks your signal. EBS, writing about analog octave pedals, makes the point directly:

EBS Sweden, support article³¹

An envelope filter is the same kind of circuit: it measures your signal, so distortion, compression and heavy gain in front of it give the envelope follower a flattened, less varied input, which can make the sweep sluggish or uneven. A compressor placed before a tracking effect can help, as EBS notes, "it helps with the control of the overtones"³¹, but the general rule is filters early, drives later.

For contrast, effects that do not track your playing are more flexible in where they sit. Reverb pedals are typically placed at the end of the signal chain or in the amp's effects loop, which prevents the reverb from becoming distorted³². Amp and cabinet simulator pedals most commonly go at the very end of the chain, feeding a PA system, audio interface or headphones³⁰. Loopers also belong at the end, so that every possible signal and effect triggered gets looped³³.

Power and connections

Filter pedals follow the same power conventions as most modern pedals, and the category spans a wide range of formats:

• Standard stompbox formats with footswitches, like the MXR, Maestro Agena and Carl Martin Ottawa^12341621.
• Desktop units switched by hand rather than stomped, like both Elta Music Polivoks filters⁹¹⁰.
• Compact mini formats, like MOOER's pocket-sized Envelope¹³ and Flamma's FC11¹⁷.
• DIY builds: PedalPCB's Lowballer Twin Envelope Filter is a printed circuit board for players who solder their own³⁵, and Lectric-fx's FAT32 Dynamic Filter is sold as a PCB set for a dynamic filter pedal³⁶.

Because a filter pedal's response depends on input level, matching your instrument to the pedal's expectations matters. Passive and active basses deliver different signal strengths, which is exactly why MXR builds the compensation into the Sensitivity knob¹⁴.

Questions to ask when choosing a filter pedal

Before settling on a filter pedal, it helps to work through what you actually want the effect to do.

• What should move the filter? Your foot (wah-style control, as on Behringer's manual mode⁸), your pick attack (envelope filters like the Agena¹²), an internal cycle (auto-filters like the AF-9⁸¹²²⁰), or nothing at all (static utility filters like Broughton's⁸¹²²⁰²).
• Which frequencies? Low-pass for darkening, high-pass for cleanup, band-pass for vocal sweeps, or a pedal like Alexander's that offers all three²³.
• Guitar or bass? Bass benefits from Dry/Effect blending, as on the MXR¹⁴, and dual-filter designs like the Aguilar Filter Twin³ or the 3 Leaf Audio Chromatron.
• How much control? A simple Sense knob suits plug-and-play players¹²; control sets like the September Sound modded wah's sensitivity, threshold, frequency and blend suit tinkerers²⁹.
• Do you want filtering alone or bundled? Pedals like the VENA CAVA FILTER (distortion, auto-filter, ring mod)²¹ or the Kilter V2 (modulation, tremolo, ring mod, clean blend)²² fold filtering into bigger machines.

New pedals show the category is still moving. The Maxon AF-9 Auto Filter remains a go-to filter pedal for players, a favorite among reviewers³⁷. The Defects FX Dirty Filter "looks and sounds like a cool creative pedal," and was added to a roundup of the best filter pedals overall³⁸. All-Pedal, whose previous pedals include the Macrodose Envelope Filter and the Love Machine Octave Fuzz, continues to build in the envelope-filter space³⁹.

Questions