For most instruments and for all vocals it is good to put compressors in the signal path, they can simply be added via the insert (if you have them) or put it inline, in between the desk and the capture device. Only use a very small amount of compression, as you don’t want to limit your mix before you’ve even started.
Let’s start my explaining all the different features on a standard audio compressor.
Threshold is the level at which you want the compression to start to effect your audio signal.
Say you set your threshold at -20db, but your audio signal never gets close to -20db, then the compression will never kit in.
On the over hand, if you set your threshold to -80db, pretty much every audio signal will be compressed by the compressor.
Ratio is the amount of compression you want to apply to an audio signal. Or you could say the ratio is the amount of audio reduction.
When an audio signal reaches the compressor threshold, the compressor reduces the sound by the amount set by the ratio.
It is common to have a ratio of between 3.5:1 and 4:1 for vocals. All depending on who dynamic the vocalist tends to be. If the signer is very timid then 3:1 would be more than adequate, however if a singer loves to shoot then a ration 4:1 or even 5:1 would be required.
Attack is simple the amount of time it takes for the compression to kick in.
If you wanted to compress a trumpet, you would normally want to use a fast attack, (although trumpets can play softly) because you will want the very start of the first note to be controlled by the compressor.
Also you might want to compress an audio signal, but you don’t want the clarity to be removed when you compress the signal, so setting a slower attack allows more clarity to be heard.
Once the threshold has been reached, hold, determines how long the compression will stay active until releasing the compression.
If you are compressing a drum kit you don’t want the compression going on and off, you want the sound to remain constant, so by using the hold dial, you can bridge any small gaps that go below your threshold using the hold dial.
Attach controls how quickly the compression is removed once the threshold is no longer reached.
If you have a peace of music that you are compressing, you don’t want the audio signal fluctuating or pumping when you are compressing it. You need to increase the release so that the compressor doesn’t come of so soon.
The last thing you want to hear is your audio signal getting louder when you audio signal should be getting quieter.
Kind of like a mix dial, it allows you to mix the about of signal that has compression with the original signal that has no compression. This dial is useful when on a mixing desk channel insert were you might not want all the sound source compressing.