Never really thought about pedals and such, and now I have my own I would like to ask 2 questions.

1) What is a compressor pedal?

2) What is a noise gate?

Please don't kill me.
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Telecaster - SG - Jaguar
Princeton Reverb, Extra Reverb
P-Bass - Mustang Bass
Apogee Duet 2 - Ableton Suite
1) A COMPRESSOR makes loud notes quieter and quiet notes louder, so you could say it "compresses" the signal. It also can increase sustain (because as the note trails off the signal is increased). It also can make the sound kinda "squishy", sorry, its hard to explain in words, just get yourself down to a guitar shop and dont be afraid to try one out.

2) A NOISE GATE cuts the sound when the volume drops below a set threshold (I think its volume, or was that frequency? Not sure, someone will verify that). Basically it removes the noise when your not playing (with the exception of high end ones like the isp decimator, which cut noise while your playing)
a compressor squeezes your signal together. soft notes louder and vice versa. it can induce noise if you use it too much. it can kill dynamics and sustain if used too much.

most noise gates are like reverse compressors. instead of amping the soft notes and limiting the louder notes, it totally cuts off the weaker frequencies along with the noise. using it too much also would kill your dynamics etc. if you can manage and tweak your rig you shouldnt need one IMHO.