Traditionally, compressors offer a range of compression ratios between 1:1 (in other words, no compression at all) and a maximum of infinity:1 (in other words hard limiting). However, even at infinity:1, signal peaks are only limited to the level of the compression threshold. There are a very few compressors, though, that offer the option of negative compression ratios, an unusual setting that can actually turn down peaks all the way to silence if necessary, and in this video I'd like to suggest a very useful drum-processing application for this. Take this dry full-band mix, for instance.

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Now let's say I wanted to add more sustain to the snare drum, but without otherwise changing the sound. What I'd do is send from the snare microphone to a parallel compressor that has a negative ratio function. (Here I'm using Melda's MDynamics plug-in.) I'd set its transfer function to a shape like this. And then adjust any attack, peak-sensitivity, and lookahead functions to completely eliminate the drum's attack.

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Now, if you're using a compressor which has no lookahead function (such as Melda's freeware MCompressor), then you can implement that lookahead function from first principles by using a time-shifted copy of the snare track as a side-chain trigger. In this example this trigger signal is coming from the light-blue track, which is only feeding the compressor's sidechain, and not the mix buss.

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Once I've got the compressor ducking the drum peaks reliably, I'll tweak the transfer function to refine the quality of the sustain I want to add.

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And now let's mix in that sustain signal to taste.

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Of course, there are plenty of people who use just regular parallel compression to achieve a broadly similar sustain-enhancing effect, but the advantage of this negative-ratio approach is that, although it clearly makes the drum feel stronger and clearer in the balance, it actually affect's the drum's peak level hardly at all. As such, it won't upset the action of any buss compression you might be using further downstream in your mix setup, and also the snare will remain strong even if all your final mix's peaks are completely steamrollered by overenthusiastic loudness processing, as in this example.

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