MXR M87 Bass Compressor

The MXR Bass Compressor (M87) is one of those pedals that just gets compression right without getting in your way. It’s designed to be transparent and professional, giving you studio-quality compression in a compact pedal format. Constant Headroom Technology means your bass’s full dynamic range comes through right up to the threshold, so you’re not losing punch or clarity before the compressor even kicks in.

Controls

Reading the panel top to bottom, left to right: Release sits top-left, Attack top-right, Output bottom-left, Ratio in the center (rotary), and Input bottom-right. Release sets how quickly the compression lets go, ranging from 50 ms all the way out to 1.1 seconds. Attack sets how fast the compressor clamps down, from a near-instant 20 microseconds up to 800 microseconds. The Ratio rotary steps through four positions: 4:1, 8:1, 12:1, and 20:1, covering everything from gentle peak control to hard limiting. Input sets the level hitting the compressor; Output makes up the gain on the other side. A 10-segment LED meter runs down the face showing exactly how much gain reduction is happening in real time.

In the demo above I’ve set up sweeps for the Release, Attack, and Ratio knobs so you can hear what each one does to the same bass line.

How It Sounds

I find this pedal excels at evening out fingerstyle playing without making everything sound lifeless. The attack and release controls are surprisingly musical: you can dial in everything from subtle leveling that barely registers to the ear, all the way to more obvious pumping effects if that’s your thing.

The presets in the demo map the range. Subtle uses a 4:1 ratio with a mid-range attack and release, which tightens the signal without announcing itself. Boost steps the ratio up to 8:1 and pushes the output, useful as a clean level lift with compression baked in. Squishy maxes the ratio to 20:1 with both attack and release at minimum, which is where the effect becomes audible and deliberate. Brick Wall keeps the 12:1 ratio but pulls the attack to zero and pushes the release to maximum, locking down transients hard and letting the compressor hang on. Punchy also uses 20:1 with attack and release both at zero and the output boosted, which is what MXR describes as effective for slap bass.

Bass Compressor vs Dyna Comp Bass

The natural comparison is the MXR Dyna Comp Bass, which is built around the vintage CA3080 “metal can” circuit. The Dyna Comp Bass has character you can hear: a squish and coloration that’s part of the appeal. The M87 chases the opposite goal, aiming to stay out of the way of your tone. Where the Dyna Comp Bass gives you Sensitivity, Tone, Clean blend, and an Attack switch, the M87 gives you independent Attack and Release knobs with specific time ranges, a four-step Ratio rotary, and a gain-reduction meter. That meter alone changes how you set the pedal, since you can see exactly what the compressor is doing rather than dialing by ear. If you want a compressor with personality and a fast learning curve, the Dyna Comp Bass is the one. If you want surgical control and a transparent result, the M87 is the more studio-minded tool.

Who It’s For

The M87 really shines when you need professional results without the learning curve of more complex rack units. It’s transparent enough for recording work and responsive enough for live performance. Fingerstyle players who want to even out note-to-note dynamics without flattening their tone will get the most from it. Slap players can lean into the 20:1 ratio for a punchy, controlled sound. The honest caveat: if you want a compressor with an audible character, this isn’t that. There’s no blend knob, and the controls reward some patience to dial in, so players who want something simple and immediate should look at the Dyna Comp Bass first.

Specs

• Controls: Attack (20 us to 800 us), Release (50 ms to 1.1 s), Ratio (4:1, 8:1, 12:1, 20:1), Input, Output
• Gain-reduction meter: 10-segment LED
• Constant Headroom Technology (CHT)
• True hardwire bypass
• Power: 9V DC, 19 mA
• Frequency response: 20 Hz to 20 kHz (+/- 1 dB)
• Dimensions: 4-3/4 x 2-3/4 x 1-9/32 inches
• Weight: 8.4 oz

Signal Chain

• JMJ Fender Mustang*, La Bella Flats* and Curtis Novak Fat Mustang pickups, played with 0.60mm Dunlop Tortex Triangle pick*
• Bass Compressor
• Bogren Digital Bassknob STD*

Where to Buy

Buy now, brag later Treat yo' self Your tone deserves this

Buy through these links and support Loopy Demos at no extra cost to you.

Get detailed specs on MXR's website

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