What is parallel compression? The simplest way to describe it is, mixing a compressed signal with it’s dry source to create a fatter sound. To do it all you need to do is send the the part you want to add parallel compression to a compressor, compress to taste (usually pretty heavy) and add back in under the dry signal to get the desired results.
Here’s how to do it basically any daw
1. Create an aux channel and insert a compressor
2. Send the signal to the aux channel.
3. Compress to your heart’s content
4. Adjust the level of the Aux track until you get the sound you want. Be aware that if your compressor induces some sort of delay you will have to adjust the original track to sync it.
Now let’s talk about another use of parallel compression. Once again I was reading Bob Katz’s Mastering Audio book and he mentions parallel compression as something that can be used in mastering. It’s the same concept pretty much but the compression is really aggressive. The compressor pretty much stays in massive gain reduction most of the time. As the dynamics of the source material decreases the compressor loosens its grip and starts to open up letting more signal through. As the source dynamics increases the compressor clamps down on the signal.
Here’s the optimal setting according to Bob Katz’s book for parallel compression.
Attack= As fast as possible (it’s really helpful if the compressor has a look ahead feature.)
Ratio=2:1 or 2.5:1
Release=250ms-350ms. Depending on the source it could be as large as 500ms. You need to be careful of the reverb tails.
Make up gain= to taste. He notes that subtle compression can be achieved with with -5dB to -15dB. Anything greater than -20dB will not be perceptible.
Some delay may be needed to line up the signals due to any delay induced by the compressor.