I used to struggle to understand how to use compression.
I use compression in two different ways.
On channel strips, I use compression as a guard rail. What I’m trying to do here is to avoid clipping the recorder. For instruments that don’t have a high peak to average ratio, I’ll set the threshold at about -5 dB, the ratio at 3:1, a hard knee and roughly 5/150 ms attack/release. For instruments with a high peak-to-average ratio, I’ll set the threshold at -15 dB with a soft knee; I also set the channel level 5 dB higher than the levels for guitar, keys, synths, etc.
I also gate every channel. In my studio, all instruments are direct; there’s no room noise, but there’s still self-noise from the devices themselves. I adjust the gate to close when the device is on but not playing.
On the mix buss I’ll use chained compressors to raise the overall level towards the streaming target of -14 LUFS. My approach here is to set the threshold as deep as possible (roughly -45 to -60 dB, depending upon the compressor), maximize attack/release times and use a small ratio (typically 1.2:1 to 1.5:1).
This buss compressor usage with deep thresholds is the one that always seemed counterintuitive to me. IME, it’s much easier to use math than one’s ears. You need to know the noise floor of your recording. You need to pick a target noise floor for the intended listening environment. If you’re going from a -70 dB studio noise floor to a -45 dB target noise floor, you’re removing 25 dB of dynamic range. The overall compression ratio in this case is just 70 over 45, or about 1.55:1. I’ll spread this across two compressors to avoid breathing and pumping; the ratios are multiplicative so about 1.25:1 for each compressor.
I have a limiter at the end of the mix buss chain in order to limit peaks, aiming for a target of -2 dBTP.
My postproduction workflow is to edit unwanted parts of the 2-track recording (this could be as simple as removing top and tail, but might also involve removing dead air between sections) and raising the level the rest of the way to -14 LUFS, with another limiter to control peaks.
