Ratio has four settings: 4:1, 8:1, 12:1 and 20:1. Attack runs from 20 to 800 microseconds and release from 50 milliseconds to 1.1 seconds. These ranges let the pedal move from light levelling to hard peak limiting.

A row of ten LEDs shows gain reduction as it happens, which makes the settings easier to judge on a dark stage. Constant Headroom Technology keeps clean headroom high, so fast bass transients pass without distortion.

The M87 uses true hardwire bypass. MXR also makes the Dyna Comp for guitar, which has a simpler control set. The M87 suits bass players who want more control than a two-knob compressor gives.