Mxr m87 bass compressor review I don’t think I’m the only one who thinks that bass compression is an underrated and often misunderstood effect. Out of the box the MXR M87 comes packaged with a user manual, sticker, and a random advertisement pamphlet for other related effects pedals. Product description MXR's M87 Bass Compressor puts studio-grade bass compression right on your pedalboard! You'll love how the M87 puts you in complete command of compression functions, thanks to attack, release, ratio, input, and output controls. The built-in Constant Headroom Technology (CHT) ensures plenty of headroom.