Extensive compressor reviews and FAQ

Boss LM-2B: This is an older version of the well-known LMB-3. For a long time I didn't bother reviewing it because on the surface it just looks like it would be the same as an LMB-3 but without the Ratio knob--and I happen to think the Ratio knob is a very important feature. However now that I've tested one, I found that it is different enough to warrant its own review.
 
The biggest difference is in the function of the Enhance knob. For both versions there is a steep narrow cut in the mids followed by a steep narrow spike of boost. But the LM-2B cuts around 1 KHz and boosts at 2 KHz, while the LMB-3 cuts and boosts at higher frequencies, across a wider slope, with steeper effect across the range of its knob-turn. The LM-2B doesn't boost nearly as much in the range above 4 KHz, so it doesn't amplify noise quite as badly as the LMB-3. Aside from the noise potential in the highs, it's up to your subjective taste which EQ effect sounds "better".
 
Below the mid-cut point of the Enhance, their frequency response is very similar, with no loss of lows. With the Enhance off, they both significantly roll down the high frequencies in a long wide slope, and the LM-2B does this even more than the LMB-3. On the other hand, you can consider it as a "bass boost", depending on how you set the output level. There is no way to get a flat signal from either pedal. Here is a spectrum analysis of both:
 

 
They have slightly different "feel"/response in their compression action, and this is because they use different VCA chips: the LM-2B uses a dbx 1252, while the LMB-3 uses a THAT 2159. They operate similarly, but not identically. In subjective terms, I feel the older LM-2B has a smoother action overall, and has less distortion in the lows when hit with a big amplitude peak. The LM-2B has a fixed ratio; it is impossible to know for sure just using my ears, but to the best of my perception I think it is somewhere between 10:1 and 20:1. This is pretty strong, and well-suited to peak limiting, but of course the LMB-3 can squash even harder at infinity:1. Also the LMB-3 has a fully variable ratio, for any range of light or medium compression, while the only way to get less squashing from the LM-2B is to raise the threshold (turning the knob clockwise).
 
Both pedals will sometimes distort a bit if you hit them with a very strong low-frequency peak, and this distortion may be heard as a slight buzz or click sound on the attack. 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.
 
Aside from the different VCA chips, the two pedals use nearly identical components, and both are built with the classic hard-to-kill Boss ruggedness. Also, even though Boss sometimes gets a bad rap for its buffered bypass switching, in these two cases there is no complaint to make--the bypass is transparent, unity gain, with perfectly flat frequency response. Overall I like the LM-2B better than the LMB-3, because of the smoother action, and because I prefer the sound of its Enhance (in moderation); but the tradeoff is its fixed high ratio.
 

 
 
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