When it comes to mixing drums, few things have studio newcomers tearing their hair out more often than compression. Is a compressor supposed to even out the levels in a performance? Or lengthen sustain tails? Or make individual hits more punchy? Or pull up low-level details? Well, compression could do any of these things, or none of them, depending on how you set the compressor up — hence all the confusion!
In this article I’d like to clarify matters by identifying a series of distinct drum-mixing tasks for which engineers commonly use compressors. I’ll explain in each case what compression settings you might choose for best results, whether the drums you’re working with are one-shot samples, loops, virtual instruments, or live recordings. And I’ll focus specifically on tackling the kinds of undesirable processing side-effects that blight many project-studio mixes. As we’ll see, this can require more sophisticated compression methods, but I’ll also suggest various alternative remedies that can bail you out when compression proves unable to deliver the goods.
Another frequent source of head-scratching amongst less experienced engineers is that so many real-world compressors have different control sets. For this reason, I’ll restrict myself to the most common configuration, found in compressors bundled with pretty much every mainstream DAW, which is based around five main controls: Threshold, Ratio, Attack, Release, and Make-up Gain. However, I won’t go over the very basics of what these controls do (check out my ‘Compression Made Easy’ feature in SOS September 2009 if you need a refresher: http://sosm.ag/compression-made-easy). Instead, I’ll concentrate on how best to set them up in practice for each specific drum-processing task.
Let’s start with the most common function of compression, whether you’re dealing with drums or any other instrument — to automatically even out unwanted level variations. In drum terms, that means turning down louder hits to more closely match softer ones, so the processed part can be more stably and reliably balanced against other instruments. Here’s how you can set up a compressor for this purpose, assuming for the moment the simplest scenario, in which I’m dealing with a single ‘instrument’, either an acoustic drum recorded live, or some kind of programmed electronic sound.
First, dial in attack and release settings of around 1 and 100 ms respectively, and choose a ratio of, say, 3:1. Then reduce the threshold until you see activity on the gain-reduction meter for all but the softest hits. You’ll almost certainly want to finesse the ratio based on what you hear. Some hits still too loud? Increase the ratio. Dynamics flattened too much? Then lower it.
While this should yield a sound that holds its place in the mix more solidly, the job’s not complete — you must also make the best of the attack and release times. For pure balancing applications, go for an attack time as fast as you can get away with, so that it catches the fast-moving transient at the onset of each hit. However, many compressors can respond swiftly enough to put kinks into the start of a drum’s audio waveform, altering the drum’s attack timbre, especially when you’re processing the slower-moving waveforms of low-pitched sounds. So make a point of listening to the attack portion of the processed drum signal while you massage the attack time, and actively choose a timbre you favour.
It also makes sense for the release time to be as long as possible, so the compressor’s gain-reduction reset occurs mostly after the sustain tail of each drum hit has finished. Otherwise, you’ll change the drum’s decay characteristics. If you set the release too long, however, the gain-reduction won’t reset fully between hits, thus weakening the compressor’s level-correction effect. So, in practice, you’ll almost always need to adjust the release to suit the tempo and complexity of your drum part. For example, you’ll...
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