Question:
what are these pedal for? can anyone help me thanks a lot
Answer:
They boost the low sounds and lower the high sounds. So for example, you strum a chord, and you play the top strings harder than you play the lower strings. Normally, the top strings would produce more noise, and you wouldn't hear the lower strings as well. A compressor evens it out more, lowering the top strings and boosting the bottome strings (or vice versa, it just evens the sound out.). It helps the signal last longer, which is why its called a sustainer as well. If you play acoustic you don't really need it, its mostly for electric guitars. Thats the best I can do explaining it, somebody correct me if I'm wrong
Answer:
Yes. it keeps the tone at more or less, a steady volume. I dunno if it can really do individual strings like that (there might be one that does...), but that's what it does, giving you a lot of sustain. Not true sustain, really. A sustainer is a totally different thing all together. It actually uses a magnetic field or a acoustic vibration to keep the string sustaining. It goes directly inside the guitar, and gives true sustain.
Answer:
A compressor evens out your dynamics by not allowing your signal to go above or below a certain volume. I guess the correct terms are "attack" and "threshold".