DelTee asked what compression was. I'll try and make it simple. Many people think of compression when they convert a wav file to an mp3, you compress it to a smaller more manageable sized file.
When sound engineers talk about compresion they mean something else entirely. A compressor or limiter in the studio refers to a box of tricks (or software these days) that acts as an automatic volume leveller.
There is only so much volume you can record onto any medium before you run out of headroom and get distortion - a ceiling if you like. What a compressor does is looks at the peaks or spikes in volume and squashes them down lower. After that's done, you can turn the whole thing up and it sounds louder. In other words, there is now less difference in volume between the loudest parts and the softest parts.
Individual instruments like a bass guitar, or vocal, can be compressed, and so can complete mixes. The result is a louder, punchier performance under the same ceiling. This is one reason why your favourite records never sound quite the same on the radio as they do at home. Radio stations all employ massive compression in the signal path to reduce the dynamic range of their output and make them sound loud on the dial.
I'll try and show you what I mean. I'm posting two soundfiles. It's the same track by the Fascinations. It's come from the master tape and I'd bet a pound to a penny this version (take8) was never mastered or compressed. It's great but sounds kinda loose.
I've taken the same track and compressed it, admitedly in a rather crude way, but trying to emulate analogue compressors of 60's.
The compressed one sounds louder - right? And tighter, and perhaps more punchy? Have I just turned up the volume? No. It's the compressor that's squashed the louder bits, allowing me to turn the gain on the whole thing up. A touch of plate reverb and it'd be ready to cut to disc.
Hope that all makes sense! Fascinations_NOT_compressed.mp3 Fascinations_with_compression.mp3