The original series as written by the mysterious Jetphase
Most people think of the compressor as a device that helps even out the dynamics of a given instrument or track. But, the best engineers and producers realize that they're much more than that. A compressor is another way to shape the tonality of a track, and even EQ it in a sense. If a track is a bit dull, using a brighter sounding compressor can give like a Urei LA-4A can give it the definition it lacks. If a track just doesn't come to the front of the mix enough, running it through a Urei 1176 can give it the personality it needs to stand out. And compressors are a great way to mangle and distort sound. Just crank up the ratio and watch out. Here are a few of the great unknowns.
Urei 7110: This compressor really has only one thing going for it: It crushes sound sort of like an 1176, but costs 1/8th of the price. Its gritty, gnarly, and generally kind of bad sounding till you put it on a drum room mic and crank it up. Then the ugly duckling becomes a swan. These are a great character piece, and are worth the price of admission.
Urei BL-40 Modulimiter: What do you get when you cross an 1176 with a Urei LA-3A? The BL-40. Inside this beast you'll find the guts of both the 1176 and the LA-3A, which makes for a very impressive piece of gear. These were actually made for the broadcast industry, but have been finding their way into more and more producers' racks because of the how great they sound on electric guitars and drums.
Spectra Sonics 610: These are one of the harder compressors to set up, as the circuit overloads very easily. Once you get them adjusted properly, they sound very similar to a Urei 1176, only trashier. Very useful for drum room mics, snare drums, electric guitars, and even bass. As long as the red overload light isn't coming on, you'll be loving it.
Alesis Microlimiter: Don't laugh. Just try one of these on a drum room mic and it'll make you a believer. Set it up like you would a Marshall guitar amp: Turn everything up. It's dirt-cheap and looks funny, but it can be a very useful tool around the studio. Its sole purpose is to screw up the sound.
ADR Compex: Remember the amazing drum sound on the Led Zeppelin song "When the Levee Breaks"? That was done with 3 mics, with an ADR Compex compressing the signal on the two overhead mics. This is a very agressive sounding compressor, and definitely one of the great unknown rock and roll pieces of gear. The aforementioned Helios consoles routinely had the ADR Compex compressors in them as their onboard dynamics processors. Guitars and drums love these things. Everything else is just infatuated.
Altec 436B, 436C, and 438: These are noisy as hell (don't use them on a mellow vocal track), but they sound absolutely fantastic on rock drums, guitars, and even bass. They have a big, fat sound, and can crush the signal without it sounding squashed. I've even used them successfully to mangle an acoustic guitar track, in order to give it more character. If it's good enough for John Lennon and The Beatles, it's good enough for me.
Gates Sta-Level: These things weigh a ton, take up a lot of rack space, look cool as hell, and do beautiful things to a bass. It's a variable mu compressor that's similar to a Urei LA-2A, but in my opinion, fatter sounding. And they're not only great on bass. Kick drums and vocals sound wonderful through them as well.
Shure Level-Loc: The Shure Level-Loc was made famous by Mitchell Froom and Tchad Blake, who use their horrible, trashy sound to add character to drum tracks. These squash the signal completely, adding all kinds of nasty distortion to the sound. They're wonderful. Track a mono room mic through one of these, and mix it in with your regular drum mics for a very cool, character-filled sound.
MXR Mini Limiter: The MXR is another crusher. The key to these is to leave yourself access to the ratio knob on the back of the unit. These are great on drums, but unlike many other character compressors, they are really good on electric guitars as well.
MXR Dynacomp: It's a guitar pedal. Try patching one in to a mono drum mic and see what happens. Some seriously cool sound mashing can be had with this pedal. It also works great in conjunction with the Boss TU-12 Tuner mentioned earlier. This is lo-fi at its finest.
JOEMEEK SC-2: It's not a vintage piece, and it's not really unknown either, but it definitely deserves a mention here. This compressor sounds incredible on bass, drums, electric guitars, and vocals. How can you use the adjectives warm, fat, round, aggressive, punchy, and detailed to describe a single piece of gear ? Try one out, and you'll know how.
RCA BA-6B: These are so cool on bass that it's beyond words. The tone is as big as the unit is, and that's freaking big. I hope you have a heavy duty rack to put this in because these weigh a ton. Many people call these the poor man's Fairchild 660. Of course that means it doesn't cost $20,000, only $3,500. Huge transformers generally equal huge sound, and the BA-6B is no exception to the rule.
Empirical Labs EL-8 Distressor: The EL-8 is a modern classic with its ability to sound like a tube compressor, a solid state compressor, a crystal clear sounding compressor and a grungy compressor. It all depends on how you set it. This is truly one of the most versatile compressors ever made, and really has the ability to take a good track and make it great. It wins first prize in the "chameleon" category.