Extensive compressor reviews and FAQ

MXR M87 "Bass" and M76 "Studio": MXR has informed me that their new M76 "Studio" comp is exactly the same as the M87 "Bass" comp. They found that guitarists loved the sound of the M87, but were turned off by the word "bass" printed on it. So the M76 is for those guitarists. And actually, I like the paint color and the knob style on the M76 better myself. This recent pedal from MXR received a lot of hype and excited interest long before it even became available in stores, because MXR took some design inspiration from the classic Urei 1176 studio rackmount comp, which many people have wished they could get in a pedal form.
First, be aware that there have been some complaints already about defective M87s on the market. The one I have in my hands has no unusual hiss, but I've seen posts from several people saying they bought one that hisses badly at all settings. Other complaints include the effect failing to engage, or responding only to extreme input levels, or having low output. Again, the one I have has NONE of these problems. And I don't know how many of those issues are due to user error. But it is only fair for me to alert you that a few faulty M87s may be out there, so if you buy one that seems to not be working as it should, your best bet may be to exchange it right away for a new one.
A big feature you'll quickly notice is the row of LEDs for metering. In general it can be quite difficult to know, just using your ears, how much your signal is being compressed--so having a clear visual indication can be a major help, especially to someone still learning how to use compression well. Very few pedal comps have this degree of metering; many have no indicator at all, while others just have a single LED that changes color or changes brightness. That one LED is good enough in many cases, but the row of them on the M87 is much easier to read. Note that with this comp circuit the interaction between the threshold and the ratio can sometimes be counter-intuitive, so the readings on the meter may not match your expectations; so just remember to use your ears too.
The next thing is the number of controls. Most pedals don't have this much control over the compression, and the ones that do tend to be larger and more expensive. The MXR has knobs for attack and release, input and output level controls, and a rotary switch to select between four ratios. The attack knob has a very narrow range, from fast to faster. The most important one is the input level control, which you will use to set the threshold (where the compression kicks in). The higher the input level, the sooner the compression starts. It has a good wide range, to accommodate very high-output and low-output instruments. The one tricky thing I found was that it can take only a tiny turn of the input knob to go from "not enough" to "too much". This is unfortunately an unavoidable side effect of having such a wide range of level control, using such a small knob. So it's not a design flaw, but it is something to be aware of, that can make things difficult at times. I strongly recommend removing that knob cap and replacing it with the largest-diameter knob you can find that will fit next to the other knobs.
The available ratios are 4:1, 8:1, 12:1, and 20:1, with 4:1 being best suited to "fattening" your signal, and 20:1 being best for peak limiting. It works very well as a peak limiter, and is well suited to slappers and aggro players. All of the ratios are useful though, depending on your tastes and needs. While it is capable of very heavy compression, it doesn't do the sort of syrupy dip-and-swell envelope effect that some people like. I find the action is somewhat similar to the 1176, but more "clinical" and less "fluid".
There is no loss of highs or lows. It has fairly low noise--it's not dead silent, but the noise level is definitely better than average. The tone is clear and dry, not perfectly transparent, but in that neighborhood. People who want minimal coloration will be pleased, but people who want "tone magic" will be disappointed. Because of the claims about the M87 being "based on" the Urei 1176, consumers may assume or wish that the M87 will give them a famous vintage tone quality. It will not. It's a great-sounding pedal, it's better than a good percentage of the other pedals out there, but it is not a magic vintage recording-studio tone box. It's just a good, clean compressor with some useful features, that happens to use a circuit and control layout similar to the basic concept of the Urei.
The housing is the same small size as other common MXR pedals. The construction quality is pretty good overall, typical for mass production at this price point, except for the ratio switch--it has a plastic shaft, so it will not last as long as the rest of the pedal. The pedal runs on standard Boss-type 9V DC, and the footswitch is "true bypass". MXR tech support says you can actually run the pedal on up to 18V if you want, with no harm, but it won't improve the performance of the pedal.
People have asked me to compare it to the more expensive FEA pedals that I talk so much about. It's neither as crisp and cutting as the Dual-Band, nor as fat and warm as the Opti-FET, and it doesn't have as much control as either of them. Also the FEA's have even lower noise levels. That said, the MXR does have much more of those good qualities than most other pedals in its price range, and it is smaller than the FEA's, and has more advanced LED metering. So overall, is it as good? No. Is it very good anyway, especially considering the price? Yes, absolutely. It has officially given Demeter and EBS notice that it's time for them to move out to a retirement home.

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