With it being one of the most commonly and practically used audio effects, I’ve talked A LOT about compression here on Music Guy Mixing. One of the most often misunderstood but impactful parameters in all of mixing is the music compression ratio on that compressor, so let’s talk about what this does and give a specific example of how this affects your audio.
What is an Audio Compressor
An audio compressor is either a hardware or software (plugin) based tool for attenuating dynamic range of audio.
It does this by bringing down the loudest peaks so that there’s less of a difference between the quietest and (new) loudest points in the audio.
By sacrificing some of the natural dynamics of the audio, this helps in more easily setting a good volume/fader position for that track and ensures that virtually every aspect of its audio is heard.
Music Compression Ratio
Every compressor has a number of different parameters/settings (see my audio compressor settings chart):
All of these settings work together to affect how much of your audio is compressed and to what extent.
For instance, there’s another parameter called the compression threshold which determines how much of your audio will be attenuated.
In music, the compression ratio refers to the parameter on the compressor which controls the DEGREE to which those peaks are attenuated.
With maybe one or two exceptions, most types of audio compressors feature an adjustable ratio parameter.
It’s measured in a simple (ratio) based formula of how many decibels in (over the threshold) are reduced to 1 decibel on the out.
So, if we have a ratio of 2:1 set on our compressor, this means that every 2 decibels which exceed our threshold (and are consequently compressed), they’ll be reduced to 1, effectively cutting those peaks in half.
My overview on the compressor ratio explained does a better job conveying this:
So if we have our 2:1 ratio set and a peak of our audio exceeds the compressor’s threshold by 10dB, it would get cut in half (10/2), being output at 5dB.
A 4:1 ratio is more aggressive; this quarters the audio which exceeds our threshold. This time, if 10dB exceeds the threshold, it would get output at 2.5dB (10/4).
As you can see from the graphic above, the higher the ratio, we get diminishing returns in such a way that there’s not a huge difference between say a 10:1 ratio or a 20:1 ratio.
In keeping with our threshold being exceeded by 10dB example, a 10:1 ratio would output that peak at 1dB (10/10) and a 20:1 ratio would output it at 0.5dB (10/20).
This keeps going until we set an “infinite” ratio, meaning basically everything which exceeds the threshold gets output at the same volume. This completely squashes and removes the dynamics from our audio so that you get virtually the same volume whether it’s the quietest or loudest parts of the audio (depending on where you set the threshold).
This is the basis of limiting; an infinite ratio which creates a ceiling which no peaks in the audio can pass.
Everything which exceeds the threshold gets flattened, making this a useful tool for maximizing the volume of an entire song which is part of the audio mastering process.
Limiting or utilizing a very extreme compression ratio is also effective in ensuring that you keep an instrument in front of the mix.
I’ll use an extreme ratio like this to keep bass track ever present or a vocal up front in a pop or rap mix (see how to compress rap vocals) when that vocal needs to be at the foreground for the entire mix.
Different music compressor ratios can be useful for different instruments, tracks, and results. More aggressive ratios like the aforementioned 10 and above work well in some situations for seriously getting dynamics under control.
In other cases, you want a gentler/lighter ratio of 4:1 or lower to simply smooth out dynamics with subtlety for more transparent results.
I put together an entire compression cheat sheet, so grab that for FREE for easy to follow visual cheat sheets for the best ratio and other compression settings to dial into every single track and instrument in your mix.
