a compressor simply "compresses" your signal... making it smaller.. so say you strum lighty and then strum really hard. the volume and sound difference with be huge. with a compressor over your signal it will not allow your signal to go over a certain point. so the "hard strum" wont be much louder perse.
or, when you see those bands and the singer is singing and you can't hear him, then he starts screaming and it's to loud... a compressor can help even out the volume by not allowing those screams to get much louder... once the signal reaches a certain point the unit starts to "compress it"....
i like to have a compressor in my fx loop because it makes my guitar sound huge and fat. but not so extreme that it sounds like an elephant is sitting on my signal.
the opposit effect of compression is called "expandsion"...
for the envelope filter.... it simply cuts out certain frequencies... like for example, a wah wah pedal is an adjustible filter. the more you push it forward it cuts out more "low" frequencies giving it that shrill "nasal" sound, and the more you rock it back it cuts out the higher ones giving it a more "sub" underwater sound...
an evelope filter is kinda like a wah switched an not rocked, and you get to chosse the freq's and the threshold of the filtering, ect... you can also make it sound like an auto wah, which is like rocking the wah back and forth at a set speed. you can get some really cool sounds out of these units if you know what you're doing.
it's all fairly complicated at first and i'm not sure if i'm explaining it in enough of a "effects for dummies" kinda way.
www.harmonycentral.com has definitions and explinations of just about every effect...
what do these effects do
