Effects data base: The MXR M-120 Envelope Filter is an analog tone modifier that produces automatic "wa-wa" effects through a voltage-controlled low-pass filter circuit. The filter's upper cutoff frequency is governed by the amplitude of the input signal, so higher input levels raise the cutoff frequency. This relationship causes the signal's loudness to directly influence the perceived brightness of the sound, creating a dynamic, touch-responsive filtering effect that follows the player's articulation.

The circuit provides two primary controls that shape the filter response. The Threshold control adjusts the sensitivity of the filtering action relative to the input signal level, determining how strongly the effect responds and how bright the resulting tone becomes. Lower sensitivity settings yield more subdued filtering suitable for accompaniment, while higher sensitivity produces a more pronounced effect for lead playing. The Attack control sets the time required for the filter's cutoff frequency to reach its peak after a note is played. At maximum clockwise position, the response is nearly instantaneous, while longer attack times introduce a delayed sweep that emphasizes a "wa" character at the onset of each note.

The pedal is compatible with a range of electric instruments, including guitar, bass, piano, and clavinet, and is intended to add dynamic variation and expressive filtering to both solo and accompaniment contexts.

Tested and fully functional and is NOS. It has the original warranty card and instructions, but I doubt they would honor it now in 2026.

Foam has been removed from inside the pedal and thin cardboard has replaced the broke down foam. About as close to collector example that's been seen recently.

A great early example from 1983 production.

Unless otherwise noted, everything included with this item is shown in the photos. Items not pictured are not included. There is a 15% restocking fee if returned.