The MXR M87 Bass Compressor gets the job done pretty easily, while still allowing for a good range of variation from basic settings.
For many bassists, a compressor is a most mysterious piece of gear. Though most can suss out that they do just what their name implies—i.e., compress the dynamic range of your signal—the task of adjusting a compressor correctly can be daunting for the uninitiated. Happily, the MXR M87 Bass Compressor gets the job done pretty easily, while still allowing for a good range of variation from basic settings.
Tweaking the Knobs
Though pedal compressors often have too few controls to provide the top-quality compression one gets from a pro rack unit—that invaluable-but-hard-to-detect quality that you don’t really notice until you A/B it with the uneffected signal or watch a channel meter— happily the MXR Bass Compressor has its own version of a rack compressor’s five most potent controls—threshold, attack, release, ratio, and gain—plus a gain-reduction meter. Although dealing with five knobs and a meter may sound daunting, the basic functions of this pedal are fairly easy to use. As the concise owner’s manual suggests, adjusting the Input, Output, Attack, and Release controls to noon, with Ratio at 4:1, is a good starting point.
To test the M87, I plugged in a P bass loaded with a Seymour Duncan Quarter Pound pickup and strung up with fresh roundwound strings. With the basic settings, the MXR easily provided a natural fingerstyle sound that revealed some compression on the meter, yet went nearly undetected to the ear until I used the true-bypass footswitch to A/B the sounds. Turning up Input and tweaking Output increased the amount of compression while keeping the volume the same.
Essentially, the Input control on the MXR Bass Compressor functions like a Threshold control on a rack unit. The Output control provides the “makeup gain” to bring back what was lost after the compressor lowered the volume. Through all this tweaking, I found the gain-reduction meter to be a handy feature that enabled my eyes to guide what my ears were hearing. The manual suggests adjusting Input until three to seven bars show on the meter. Three bars on the peaks provides just a little compression, while seven bars knocks down the peaks considerably—especially on the lower notes that pack more energy.
Know Your Limits
Most adjustable compressors can also serve as a limiter by changing the ratio to 20:1 or higher and dialing-in fast attack and release. This is a useful setting for slappers who want to even out the sound without backing off on their attack. I tried this on the M87, turning both the Attack and Release controls fully clockwise for the shortest times and setting the ratio to 20:1. I then adjusted Input until I saw the gain-reduction meter quickly peak toward the left and return to the right. The actual attack and release times are not labeled on these controls, but it’s easy to remember that clockwise rotation creates faster times. From there, rely on your ears and the meter.
Either as a compressor or a limiter, the M87 did its job remarkably well. It added no noticeable noise to the signal and left my bass lines intact—as long as I didn’t get too wacky with the settings. Its compact size makes it a handy tool for real-estate-conscious bassists, and the small, sturdy knobs feel ready for many a gig.
Unlike some compressor pedals I’ve tried, the M87 was good at doing its job without having a negative impact on tone. Some two-knob compressors can become obtrusive if you’re not judicious with the settings, overly squishing the sound while adding a bit of noise along the way. It takes just a little bit more effort to set up the M87, but the bright, three-color gain-reduction meter serves as a helpful guide.
I would have liked easier access to the battery compartment, because changing the 9-volt battery requires removal of four stainless-steel screws. I had a little trouble reinstalling one of the screws, especially after it tried to cross-thread into the softer aluminum box. This is of little concern if you’re using wall-wart power, but I wouldn’t want to change its battery on a dimly lit stage. Some bassists might also prefer a compressor with variable or higher ratio options for limiting, though a 20:1 ratio is more than enough for most limiting purposes. Overall, if you’re trying to avoid hauling a rack around and have room on your pedalboard, the M87 can become a handy, valued addition to your rig.
you’re looking for a transparent, flexible compressor and can deal with multiple knobs.
you require fully variable ratios or a one-knob, set-and-forget compressor.
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