MXR Bass Compressor

I use it as a mild dynamic range compressor, it generally is on for the E string and sometimes the A.The effect is subtle, evens out the note volumes and adds a little to the sustain the way I have it dialed in. You can use a compressor for other things, but that's what I wanted it for. Another reviewer said a compressor on bass is better felt than heard, that's exactly right, it makes you seem like a better player, and makes it easier on the sound guys because your peak volume is more consistent.I had to front-end it with the MXR-M81 preamp since I have a passive bass. This pedal is not intended to be used as a preamp from what I can tell, it adds some hiss and doesn't have enough gain to be effective for that purpose, my bass couldn't even light up the lights on highest gain. But if you hit it with line-level inputs it shines.It appears to draw power from the moment you plug in to the input jack, turning on bypass does not appear to stop current draw like the tuner and preamp pedal do, so keep that in mind when you are figuring battery life. I learned this the hard way. A nice feature is when the battery dies it silently goes into bypass mode. A few of the LED lights stick on for a while as a low battery indicator, but it's already in bypass mode when you see that.My settings are 12:00 for input, output, and attack, 3:00 for release, and 4:1 ratio. My low E string hit hard will almost light up all the LEDS, the A string not so much, and the D and E hardly at all, so mostly it stops the E from overpowering the rest of the strings. When played softly I don't hit the limit so my soft dynamic range is still accessible for expressiveness o soft parts, and cleans me up a bit on the loud ones. I love this pedal and won't play without it now. Wish I had bought it years ago.

The M87 has a quite a few features that the others do not have. The first noticeable difference is the LED meter. While this is almost common nowadays on rack mounted compressors, it is not on pedals. I found the meter to be quite helpful in adjusting the input and output controls, along with the release, attack, and ratio adjustments needed to get the performance out of the pedal that I wanted.Another great feature of the M87 is the input and output ratio. I was able to adjust my input at a higher level, and keep the output at a lower level to give a more balanced and level sound for the different styles and techniques used. The M87 also has a foot switch that allows you to have the pedal on, or in true bypass mode with a blue light as an indicator to let you know which mode is currently functioning. The M87 can be powered with one 9 volt battery or with an adapter/power supply. The housing is small and durable. Everything is detailed to read in an easy way and this device is a powerhouse that everyone should have in their lineup. The instructions that came with the M87 are very thorough, which makes it easier for those that may not yet fully understand the aspects and effect that a compressor can have on your sound.

SUMMARYIt passes the low frequencies a guitar compressor will chop off. It's a good, fairly transparent compressor that imparts a soft edge on the notes, and it's a full range compressor suitable for bass, keyboards or any instrument. It's a little harder to dial in than some bass compressors as it has 4 fixed compression ratio options, then attack, release, and input/output levels. But if you read the manual it's easy enough to get a good sound. I like the LED meter and the indication of when the pedal is engaged vs. not engaged. I found the sound slightly duller than I wanted...kind of a "soft edge" on the attack. It's good, but I liked the Keeley better on that front. And the fixed compression ratios vs having a sweepable ratio knob ended up being less than ideal. It's a great bass compressor though and will work well for any bassist and be durable and functional for probably decades. On value, I don't understand why bass compressors are being MSRP'd at $199 while high end guitar compressors are $129. So the value isn't great. But solid 4 stars, probably 4.5.PROS- Good Build Quality- LEDs are visible in pretty much all positions of the knobs/placement of the pedal- LED meter provides an indicator of how much compression is occurring- Sounds good, although a softer edge than I liked on the attack, even with attack turned up fullyCONS- Value isn't great- I had to read the manual to figure out how to really dial it in correctly so it's less intuitive than some, but once you get it, it's very good.- Has a bit of a soft edge on the note attack that I felt limited my ability to cut through the mix and negatively impacted dirt sounds like fuzz. turning up the highs and mids at the preamp helped some but the Keeley was slightly better in that regard.COMPETITIVE COMPARISONThe only guitar compressor I found (and I tried several...keeley, truetone, Xotic, and a couple others) that could somewhat compete with the bass compressors was the TrueTone (Visual Sound) Route 66 compressor +overdrive pedal. It has a bass boost that helped bring back some of the low frequencies that were chopped off by the compressor. I'd generally say if you want to use a guitar compressor with your bass...just don't. The bass compressors pass more low end than any guitar compressor and you want that as a bass player.I compared the MXR bass compressor and the Keeley bassist side by side. I found them both to be excellent compressors for bass.The keeley was easier/more intuitive to dial in, and I liked the overall sound slightly better as it had a little more treble or a bit sharper edge on the attack of notes. However, the keeley has awful LED design that is confusing as to when the unit is engaged vs not engaged and I constantly have to double check that at the start of gigs and practices, and even knowing that...still have had it off when I thought it was on. Which sounds stupid but it's just not intuitive. They also laid out the knobs in an upside down V shape and the center knob obstructs the view of the blue LED in various positions depending where you put your pedalboard and where you are standing relative to it. So I hate the LEDs on Keeley...enough that I bought the MXR.The MXR on the other hand, has more visible LED indicators, and it can be controlled to a greater degree on attack and release, but not on the compression ratio which has 4 preset levels. The keeley only has a sweepable compression ratio, and a Threshold knob.I ended up keeping the Keeley and returning the MXR because I'd have had to sell the keeley at a loss and it also cost me $5 less than the MXR (both on sale $169 vs $174). I really wanted to keep the MXR, but I ended up liking the sound of the keeley better and the overall easy dial-in better. But I think at the same price and if I didn't have to take a loss on the keeley to unload it, I'd probably have gone with the MXR. That LED thing drives me nuts on the Keeeley, but the sound is the most important and in my situation, losing money on the Keeley reselling it was also a factor in just keeping it.Depending what kind of music you play and whether you use other effects might determine the best choice of compressor for your use. Both the MXR and the Keeley are great compressors, and they are both overpriced in my view. So it might also just come down to which one you get the better price on.Whatever you choose, I'd opt for a full range compressor if you are a bass player. Guitar compressors chop the low end. All of them.