Dynamic range compression is an effective way to bring more control and energy to a clip of audio. Let’s talk about dynamic range itself and why dynamic range compression is so useful in mixing.
What is Dynamic Range
First let’s identify what is dynamic range. Dynamic range refers to the difference between the quietest and loudest practical points in a clip of audio.
In this clip of a recorded vocal, we have quieter delivered words and syllables which bottom out around -20dB (20 decibels below the point of clipping).
There are a couple words or syllables which top off at -6dB (6 decibels below the point of clipping).
This accounts for a difference of 14 decibels which is the dynamic range of that vocal recording.
Admittedly there are small stretches even shown in the clip above between words or even breaths which aren’t part of the performance, but for the purposes of actual musical content which we want, the difference is 14dB.
We also have the dynamic range associated with different bit depths.
Here the dynamic range refers to the difference between the recently talked about sound of the noise floor and the point of clipping.
Recording at higher bit depths allows for a greater dynamic range between the two extremes, allowing you to capture audio at higher resolutions which are cleaner and clear of the noise floor.
Specifically, recording at 16 bit depth has 96dB of dynamic range (16x6dB). Recording at 24 bit depth has 144dB of dynamic range (24x6dB).
That’s 144 decibels between the noise floor and the point clipping which is more than enough dynamic range to work with to achieve clean recordings.
Dynamic Range Compression
In general, the dynamic range associated with a recording is natural. For instance, with the above vocal, you’d expect highs and lows and transitions in the volume when someone is singing.
When they’re belting out a difficult to hit part, they’ll need more air and force behind the notes, resulting in a higher amplitudes.
Dynamics are interesting as they figuratively keep the listener on their toes when they’re listening. If someone sang every word of a song at the exact same volume, there’d be no expression behind it and we’d lose the listener’s attention quickly.
So having established that dynamic range is a good thing, why would we want to attenuate it via dynamic range compression, i.e. applying a compressor to a clip of audio?
As I covered in my overview of what is an audio compressor, this is a device either hardware or software based which primarily pulls down the peaks or loudest instances of a clip of audio, thereby reducing its dynamic range.
Dynamic range compression offers a number of advantages:
Practical Range
While 14dB for a vocal clip is natural, it’s also too much dynamic range.
Having too much of a swing between the quietest and loudest instances of your track means that it will be impossible to properly set the level in your mix unless you’re ready to automate the level throughout the entire performance.
Setting the level of a track is much easier when the compressor is pulling down those words or notes which want to jump up and out of the mix, delivering a more stable and practical range.
Keeps Tracks Present
Dynamic range compression reduces that range so that you only have the difference of a few decibels between the quietest and loudest instances of your audio, meaning every word, every syllable is heard, while still placing an emphasis on the belted and louder instances.
This keeps the track present and up front in the mix throughout the entire performance.
Body and Sustain
To be more visible in the mix, some tracks need a bit more thickness and/or sustain on their back end. Compression not only brings down the loudest instances but brings up the quieter bits via makeup gain. A snare’s body and fade out tail gets pulled up via makeup gain so that we get to hear more of the sustain which adds or better said brings out more of the thickness of that snare into the mix.
Energy
Louder tracks have more energy by definition. Dynamic range compression makes a track louder more often, so heavily compressed tracks (or mixes) feel like they have a lot more energy to them as they’re up in your face and constant more often.
Of course you don’t want to go overboard with your compression as otherwise you’ll get the classic “sausage” effect:
This is what overly compressed audio with virtually no dynamic range looks like. There’s virtually no change in the volume from one beat to the next in this clip. Do this with your track or entire mix and you’ll lose the listener’s attention throughout listless repetition of the same volume hitting their ears over and over.
It’s all about finding that sweet spot of preserving enough of those dynamics to keep the listener engaged while getting the benefits of the compressor.
Knowing how to compress different instruments can be a minefield, setting the proper ratio, knee, attack, and release to preserve transients, get transparent and natural sounding compression while still enjoying its benefits.
That’s why I put together my free 100+ page illustrated compression cheat sheet with dozens of images to show you the exact settings to quickly dial in to every instrument in your mix to get the best results from your compression, so grab that if you haven’t already.