Multiband compressors offer unique advantages over their broadband cousins — but they also present some perilous pitfalls for the unwary.
For a long time, multiband compression was viewed primarily as a mastering tool, but its increasing availability in recent years has led more and more people to explore using it earlier in the production process. These days, in fact, I find myself using it much more often for mix processing than for mastering applications, so in this article I'd like to explain what all the fuss is about by sharing some of my favourite mixdown tricks for multiband compression.
One application is where a sound's high-frequency transients are becoming overbearing. I frequently encounter acoustic-guitar recordings with excessively sharp pick noises, for instance, and it's also common to hear unpleasant stick-contact spikes on cymbals where overhead mics are placed directly above them pointing downwards. In both these cases, the transients primarily manifest themselves as fleeting high-frequency level peaks, and you can target these using a multiband compressor's uppermost band. You'll need to use a very fast attack time in that band, of course, and a fast release time also makes sense so that the compression doesn't duck high-frequency events immediately following each transient.
Once you've set your threshold so that gain-reduction is triggering reliably just on the transients, you can then refine the compression ratio to rein them in to taste. I'll regularly use ratios upwards of 5:1 here, and you may need gain-reduction values of 12dB or more in extreme cases to smooth extra-prickly recordings, especially if you're generally boosting the brightness of your guitar or drum kit for mixing purposes. This might seem like over-processing, but in practice the speed of the gain reduction is so quick that it won't be anything like as audible as you'd expect. A critical setting in this scenario, however, is the crossover point between the compressed band and the remainder of the spectrum: set it too high and you won't be able to reduce the...