Does every instrument need compression?
This question may lead many folks to say “absolutely not, over-compression is horrible!”
But this statement can be qualified by defining “over-compression.” The term itself must have been derived from the fact the you can hear the compressor working.
A well designed and properly adjusted compressor should not be audible! (Of course this can make a well designed compressor difficult to demonstrate.) Therefore, the over-compressed sound is likely to be an improper adjustment on a particular instrument.
Why do many consoles put compressors on every channel?
The answer is simply that most instruments need some form of compression, often very subtle, to be properly heard in a mix.
Why are noise gates needed?
Consider the compressed vocal example above and you now have a 20 dB dynamic range for the vocal channel.
Problems arise when there is noise or instruments in the background of the vocal mic that became more audible after the lower end of the dynamic range was raised. (air conditioner, loud drummer, etc.) You might attempt to mute the vocal between phrases in an attempt to remove the unwanted signals, however, this would probably be disastrous.
A better method is to use a noise gate. The noise gate threshold could be set at the bottom of the dynamic range of the vocal, say -10 dBu, such that the gate would “close” out the unwanted signals between the phrases.
If you have ever mixed live you know well the problem cymbals can add to your job by bleeding through your tom mics. As soon as you add some highs to get some snap out of the tom the cymbals come crashing through, placing the horn drivers into a small orbit.
Gating those toms so that the cymbals no longer ring through the tom mics will give you an enormous boost in cleaning up the overall mix.
Thanks for PreSonus for this information.