The Mu-Tron III is an envelope filter: a pedal that sweeps a filter up or down in response to how hard you pick a note, rather than to a rocking treadle as on a wah pedal. Guitar World describes it simply as "an envelope filter called the Mu-Tron III"1, and Premier Guitar's reviewer goes further, calling it "the first voltage-triggered filter effect"2. The maker, Musitronics Mu-Tron, lists the current version as the "Mu-Tron III+ Envelope Controlled Filter"3, and the Mu-Tron III Vintage Silver as an "Analog Envelope Filter" with "envelope control of filter"4.
What it does to your sound
An envelope filter tracks the dynamics of your playing and turns them into filter movement. GuitarPlayer, in a rig rundown, put it plainly: "the filter responds to your attack and touch"7. Play softly and the filter stays put; dig in and it opens up, producing the vowel-like sweep players associate with funk and jam-band parts. The same piece describes a player running a pair of Mu-Tron pedals, "One is set to an octave down, and the other to an octave up"7, a hint at how the design gets used in practice.
Because the pedal is tagged by its own maker as both "Auto Wah" and "Envelope Filter"4, the two names effectively describe the same territory here: a filter driven by your playing rather than by your foot. That puts it in a different family from a hand-wah, and the site's filter pedals page covers the wider field.
History and status
The original was made by Musitronics5. That Pedal Show, in their introduction to auto wah and envelope filters, list the Mu-Tron III as "Discontinued"6. The pedal's reputation has carried on among players: Tim Mahoney, who uses it heavily on songs like "Amber" and "Champagne," calls it "the warmest, most badass filter out there, bar none"8.
The versions a player is likely to meet look like this:
The original Mu-Tron III is discontinued6. The current route to the design is the Mu-Tron III Vintage Silver reissue from Musitronics Mu-Tron4.
What players and reviewers say
Tim Mahoney, in a Premier Guitar interview, was blunt about his:
"It's the warmest, most badass filter out there, bar none."
He added, "I use it pretty heavily on songs like 'Amber' and 'Champagne,' and on the new album it's used a lot on 'Sand Dollar.'"8
The Behringer B-Tron III
Behringer now makes the B-Tron III Envelope Filter, which it markets as a "Vintage Auto-Wah Envelope Filter with 3 Filter Types, 2 Direction Modes and Versatile Input Range"9. Behringer describes it as a pedal that "creates a 'Wah' or 'vowel' sound every time you play a note"9. It arrives after the original Mu-Tron III, which is listed as discontinued6.
Its headline features, as Behringer lists them:
Videos
BassTheWorld.com
Justin Goodman
Mike iLL
Questions
What is a Mu-Tron III envelope filter?
It is an envelope filter, a pedal that sweeps a filter in response to your picking attack and touch, producing a wah-like or vowel sound as you play. Guitar World describes the Mu-Tron III as an envelope filter, and Premier Guitar calls it the first voltage-triggered filter effect. The maker lists it as an Envelope Controlled Filter, and the current Vintage Silver version as an analog envelope filter with envelope control of the filter.
Is the Mu-Tron III still made?
The original Mu-Tron III is discontinued, as That Pedal Show noted in their introduction to auto wah and envelope filters. However, the Mu-Tron name is active again: Mike Beigel reacquired the name in 2018, and Musitronics Mu-Tron now sells a Mu-Tron III Vintage Silver analog envelope filter alongside newer designs such as the Micro-Tron III and the Ripper envelope filter.
Who made the original Mu-Tron III?
The original Mu-Tron III Envelope Filter was made by Musitronics, as Pedal of the Day notes in its coverage of the Mu-FX Tru-Tron 3X, a later version built by the original inventor. Mike Beigel reacquired the Mu-Tron name in 2018, and products are again manufactured and sold under the Mu-Tron brand.
Is the Behringer B-Tron III a copy of the Mu-Tron III?
MusicRadar, reporting the B-Tron III's launch in February 2025, describes it as an homage to the Mu-Tron III and a Mu-Tron III clone, noting more than a passing resemblance in the metal enclosure design. Behringer markets it as a vintage auto-wah envelope filter with three filter types, two direction modes and a versatile input range, priced at 69 dollars at launch.
Is an envelope filter the same as an auto wah?
The terms are closely related and often used together. Musitronics Mu-Tron tags its Mu-Tron III Vintage Silver as both Auto Wah and Envelope Filter on its product page, and Behringer calls the B-Tron III a vintage auto-wah envelope filter. Both describe a filter that responds to your attack and touch rather than to a rocking pedal, as on a wah-wah pedal.
What is the difference between the Mu-Tron III and the Micro-Tron III?
The Micro-Tron III is Mu-Tron's compact, updated incarnation of the original Mu-Tron III. Pedal of the Day's 2019 review presents it as a smaller pedal with a new Level knob and an Up/Down footswitch added. The original Mu-Tron III remains the larger vintage design, available again as the Mu-Tron III Vintage Silver.
Sources (9)
- How the Mu-Tron III became a vintage pedalboard icon, Guitar World, 2026-02-09
- EarthQuaker Devices Spatial Delivery Review, Premier Guitar, 2016-08-17
- Mu-Tron III+ Envelope Controlled Filter, Musitronics Mu-Tron
- Mu-Tron III Vintage Silver, Musitronics Mu-Tron (mu-tron.com)
- Mu-FX Tru-Tron 3X™ Envelope Filter, Pedal of the Day, 2016-04-19
- That Pedal Show, That Pedal Show, 2017-11-17
- Inside Peter Frampton's Gear Vault, GuitarPlayer (www.guitarplayer.com), 2021-08-02
- Tim Mahoney’s Top Five Oddball Pedals, Premier Guitar, 2014-10-20
- B-TRON III ENVELOPE FILTER, Behringer
Tim Mahoney
