What is electronic noise?
Imagine that you are in a really big room, which is very quiet. Way
across the room somebody is whispering and you want to hear them from
where you are. You put a microphone in front of you, with an
amplifier, and make the amplifier amplify alot, trying to make that tiny
voice become loud enough to hear. In the end you cannot just amplify
endlessly, all you will be amplifying is electronic noise. You pick up
that hummmm in the speakers, and you don't hear the tiny voice across
the room -- its there on the speakers, but it is drowned out by the
noise from the electronics.
You cannot amplifiy something, make it bigger, without degrading it just
a bit. Just like you cannot make perfect copies on an office copy
machine. copy copy copy, and eventually it gets fuzzy. same with
amplifiers. usually tho the "voice" is strong enough that you don't
NEED to amplify that much, and you can hear it out the speakers OK.
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Update: June 2012