Pretty much self explanatory, distortion pedals make your guitar sound, well, distorted. Generally, this has come to mean everything from smooth tube overdrive to all manner of nasty, dirty, "my amp is exploding" tones and "scooped mids" pedals for death metal madness. The earliest example of distortion used in popular music was the three-note riff that was heard all over the airwaves when the Rolling Stones recorded "Satisfaction" (which, incidentally, was voted the number one rock song of all time by MTV). Jimi Hendrix loved running several pedals in sequence, like a fuzz, a wah and a "Uni-Vibe" (which we'll discuss in a bit). In fact, over 30 years after his tragic death, Jimi was still voted the world's greatest guitar player! Can you imagine having that kind of impact after a brief four-year career?
Originally described by critics as a "war toy," the wah-wah seems to go in and out of fashion. Eric Clapton used it to great effect on Cream's classic "White Room" and "Tales of Brave Ulysses" while Jimi Hendrix used it on many of his most memorable songs, which include the classic "Voodoo Chile (Slight Return)." Vox has reissued its classic wah pedal, while newer models are available from Tech 21 (the "Killer Wail") and Dunlop.
Early rock music used tape-based delays to produce everything from fast "slapback" echoes to the wild, multiple delays produced by units such as Roland's Space Echo. Later, in the 1970s, analog delays were introduced that could produce delays as long as two seconds or more, though the delays quickly lost a lot of high frequency information. The 1980s saw the introduction of the modern digital delay which could produce a wide range of full-frequency time-based effects, like chorus and flange, as well as traditional echo..echo...echo...
This is the first of our time-based effects. When a slightly detuned and delayed "clone" of a guitar signal is played back with the original, it produces a subtle (or sometimes not-so-subtle) doubling effect, which produces a thicker, lusher tone. The original effect was produced by the Boss CE-1 Chorus Ensemble, though later effects would add multiple detunings and delays to produce a rich, glossy animation. Andy Summers of The Police was quick to use the chorus effect, and it has only gotten more popular over the years.
The earliest "flanger" effects were produced by playing back the same sound on multiple tape decks, while the engineer used a finger on the tape reel's edge (or flange) to speed up or slow down the duplicate signal. This produced a wild jet-like sweep of the material's harmonic structure. Eventually, the effect was duplicated using advanced digital delays set to extremely short delay times and inverting the signal's phase.
Which brings us to...
Another time based effect that's somewhere between the extremes of the flanger and the glossiness of the chorus pedal. The groovy swirling effect is all over the first two Van Halen albums. Early Phasers were supposed to recreate the complex sound of a B-3 Leslie cabinet, which had a rotating horn and a spinning drum under a 15-inch woofer. Though the sound wasn't really close, it was better than hauling around a 250-pound Leslie cabinet. It's now become a stage and studio staple.
Jimi Hendrix loved the original Uni-Vibe, which was sort of a rudimentary chorus effect with some detuning effect similar to vibrato. The original pedals (when you can find one) fetch astronomical prices, but the watery textures have now been duplicated via digital modeling and in some "botique" stomp boxes. The late Stevie Ray vaughn and Eric Johnson have both been known to use this signature sound on their albums.
This is a classic studio effect that found its way into various stomp boxes in an effort to increase sustain. The earliest units were fairly noisy, but modern compressors have added noise gates that cut off the signal once it reaches a particular level.
Best known in its earliest incarnation in the Mu-Tron III Envelope Follower, which was actually part auto-wah and part triggered filter. Almost every manufacturer has some sort of version of this classic effect. In fact, you can't walk through Sweetwater's guitar demo room without tripping over a dozen or so . . . just kidding.
The king of effects boxes is the multi-effect pedal, which can include everything above and a bunch of stuff that hasn't even been categorized yet. These are available in all flavors from basic to complex. And by complex, we mean chaining so many effects that it doesn't even sound like a guitar any more. These monsters can replace a whole truckload of stomp boxes that tend to end up in your gig bag all tangled together (when they're not busy chowing down on 9-volt batteries).