Extensive compressor reviews and FAQ

Boss LMB-3: This workhorse classic from Boss gets overlooked far too often. Sometimes because it's a Boss, and sometimes because it says "Limiter" in the name. In reality it is one of the most reliable and versatile compressors in its price range.
The first thing to clear up is the "limiter" label. A limiter is just a compressor with a very high ratio, and usually with the threshold set high so only the taller peaks are affected. The LMB-3 can be used that way, but its ratio can be adjusted anywhere from 1:1 (a clean uncompressed boost) through light to medium smoothing and squeezing (e.g. 2:1 to 8:1), all the way up to infinity:1 hard peak limiting. So it actually covers a much wider range of dynamic response than most pedals labeled "compressor". And the threshold knob covers a decent range, allowing it to affect just as much of your signal as you want. The predecessor of this pedal, the LM-2B, was more accurately called a limiter due to having a fixed very high ratio.
In my previous review of this pedal, from about six years ago, I said the high frequencies were "clear and present"; this is not true at all settings. With the Enhance knob turned down, it actually rolls the highs off in a long slope starting around 600 Hz. The higher you set the Ratio knob, the more the highs get cut; at a very low ratio it is not so noticeable. Turning the Enhance up brings back the highs, but also produces a sharp scoop in the mids (centered around 2 KHz). Check the review of the older LM-2B for an RTA chart comparing the frequency response of both pedals. The only way to get a flat EQ with this pedal is to turn the Ratio knob to minimum, 1:1, making it a clean boost instead of a compressor. Turning the Enhance up amplifies any noise in your signal path, so between the noise and the mid-scoop, I advise using as little as possible of that knob. I wish they had included an attack control instead.
Aside from the EQ shaping, the tone of this pedal is very clean and dry. It's not a "fattening" effect, aside from the inherent results of compression. And unless you turn up the Enhance, there is not much added noise. Feeding in a very strong signal, or a big low-frequency peak, can result in distortion. This can be heard as a slight buzz or click sound on the attack, or a rough quality in the lows. It's not too bad mostly, and will not be heard in a live band mix. Some users say they have never heard this sound, and I don't hear it with my passive non-boosted basses, so it will depend on your individual signal and settings.
There is no LED to indicate the signal crossing the threshold. The construction quality is not fancy, but it is rugged and dependable. Also, even though Boss sometimes gets a bad rap for its buffered bypass switching, in this case there is no problem--the bypass is transparent, unity gain, with perfectly flat frequency response.
While clearly I have a few complaints about this pedal, the fact is it sounds pretty good and does its job like a champ, and you can find one used for very cheap any day of the week, so it's a great value. It's also hard to find any other pedal in this price range that works so well as a peak limiter, for aggro playing, slapping, or peaks from an envelope filter. I would not hesitate to use one on a pro gig, as long as the inherent EQ shaping is suitable.
A few people have modded the LMB-3 for various improvements; I recently got to spend some time testing out the Steve McKinley "Thunder" modded version, directly A/B'ing it with a stock LMB-3. The mod mainly consists of replacing several electrolytic caps in the signal path with non-polar box caps, changing some of the values. This particular mod has two clear results: it retains the high frequencies better, and the low frequencies get compressed more strongly. So it has a tighter, brighter sound, and it is even more effective as a peak limiter. The Enhance knob offers more boost in the treble, but otherwise it's the same as the stock version. Oddly, the modded pedal has lower output volume than the stock one. McKinley claims the mod "increases clarity, lowers the background noise, improves signal integrity and adds more punch". I would agree that allowing more treble does increase clarity, and compressing the lows harder could seem punchier, depending on personal taste. The noise level is NOT improved, and I'm not sure what he even means by "integrity" here, but the tone is not any more transparent. His price for this mod is $59. It is worthwhile if you want the specific qualities I've described here, but I don't think everyone would find it that much of an improvement.

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