How do you know when a song requires compression or not, what is it I'm suppose to focussing on in the mix to determine if compression can help or not its very confusing.... it sounds fine to me but a person whos been doing recording for years seems to always have a hitch with something and say it could do with a bit of compression... But then i don't know what the compression is meant to achieve ? Equal volumes on all tracks or equal volumes on all frequencies :S ? Confusing. Any advice?