Yeah, we know that compressors 'reduce the dynamic range of the audio that’s passed through it blah blah' and yeah, they’re 'used in every mix blah' but they’re still one of the most misused and misunderstood effects available, and can be a bit daunting. Still, they are definitely the coolest sounding of all the gizmos.
So. I've written a series of posts that cover the basics of what each compressor setting does, gives you a quick tip on how to always set the ‘correct’ compressor settings, and gives you an introduction into a more advanced compression techniques like 'Serial Compression'. These are basically just the facts I wish I'd had when I was trying to understand how to use compression. I know there are YouTube tutorials and articles written on this already, but I intentionally wrote this to be a nice reference that you can refer back to when you feel that twinge of insecurity about setting one of those knobs. Once all parts of the series are out, I'll put it together in a free PDF that you can download and keep on your desktop. If you like, you can print it out and give it to your loved ones as a gift. You know, if you want.
If you want clarification on anything, just let me know and I'll find another way to explain it.
Let’s recap the basics in 'real language' that normal people use - refer to the pic above to jog your memory of the common parameters. OK, let's go through what all (well, most) of those knobs do, yeah?
1. Threshold: The level (in decibels) at which compression kicks in. So, once the audio level goes above (is louder than) that level, compression kicks in and starts to make the audio quieter (assuming the ratio is above 1:1). Changing this has the biggest impact on how much compression is happening.
2. Ratio: This is just a way to explain how much the compressor is reducing the level of the audio; it’s the ratio of gain reduction between the output and the input. So, a 2:1 ratio means that once the signal goes above the threshold, the audio is reduced by half – so if the signal is 2dB over the threshold, the signal is reduced to 1dB. If the signal is 10dB over the threshold, the signal is reduced by 5dB. Ratios of 10:1 (or higher) approach limiting – a 10:1 ratio results in a 90% reduction in size!
3. Attack: This is the time it takes for the compressor to start compressing once the audio goes over the threshold that you set - set it too short and you’ll lose the ever-important transients (of course, maybe that’s what you want!). For most occasions, try to make sure that your attack time is long enough to let ‘enough’ of the transient pass through, especially on a drum bus. On the master bus or a drum bus, I like longer attack times like 30ms (with an SSL-style Bus Compressor for example, the slowest setting), so that the kick can come through and isn't 'clamped down' or becomes too thin.
4. Release: How long it takes for compression to stop once the signal is below the threshold. Setting this too fast can result in distortion (which can be cool) - too slow and you’ll run into pumping (or breathing). Pumping occurs when the compressor’s release time is long enough so that when the input signal is once again above threshold the threshold, the compressor is still acting and the incoming signal is compressed more than the previous transient (you might need to read that a couple of times). This causes the overall loudness of your track to fade in and out, creating a pumping effect. It generally doesn't sound great.
You may well find that using the same Attack and Release settings on different compressors sounds wildly different – so be sure to set these using your ears. Or the method that I'm going to outline very soon... 😎