How To Use A Compressor

Compression can be an intimidating tool which might be hard to get to grips with for a number of reasons. The first and probably most obvious being the various controlling parameters which impact one another. Each parameter is equally important when it comes to sculpting your soundscape, and you often need more than one to get the desired result.

That’s just the thing about compression, it can go overlooked when you’re busy eradicating strange pops, plosives, sibilance, those jostling clicks of saliva against guests cheeks while they talk, not to mention regular background hummings and so on. 

Why Compress?

Compression is extremely important when it comes to things like average loudness because, really, that’s all compression is – reducing the dynamic range of audio. It reduces the gap between the quietest point in your recording, and the loudest point. Unfortunately for people like me, while that might be an easy-to-understand one line explanation of what compression is, it doesn’t exactly paint a working picture of what I, or anyone else, actually needs to know about a compressor in a given situation.

But before moving on to each individual part of a compressor and what they are used for, it is also good to know what not to do when using a compressor. I remember once receiving an interview from a gentleman who had recorded himself on his laptop. And, fortunately, he wanted me to edit it. For free! I suppose you get what you pay for because at the time, I knew about as much about compression, as he did about recording audio – which wasn’t a whole lot!

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Just remember, if you’re ever unsure about what you’re doing, keep in mind that the most vital tool you can have when using a compressor is your ears. If it sounds wrong to you, then it will sound wrong to everyone else.

Threshold and Ratio

To start, let’s look at the good old friendly threshold. The threshold tells you the limit of the volume. For example, if your threshold is set to -10 dB, then every signal that goes above that point will be pushed back down or, well, compressed.

That part is simple enough. Unfortunately, the next most integral part of a compressor is also the parameter I initially had the hardest time wrapping my head around: the ratio. The ratio refers to how much the signal gets pushed down by once it passes the threshold.

Who would have guessed that using something called ‘the ratio’ would mean actually having to deal with ratios and understand them on some basic level? I can see my ordinary level maths teacher outright pointing and laughing at me now. I’m only joking, she was a lovely woman, if not a bit of a pushover. In any case, I’m not about to start pointing fingers but I am very bad at maths.

Still, let me attempt to break this down. If, for example, you set your ratio at 3:1, this means that for every 3 dB the signal is above the threshold, the output will only poke its head 1 dB above that threshold. A lower ratio means less compression, higher ratio means more compression. Realistically, you won’t need anything above a ratio of 5:1.

As stated above, compression reduces the dynamic range of audio, so you do have to listen out for subtle differences that too much compression can introduce to your audio. Oftentimes this difference is described as audio not “having room to breathe”. Once again, it’s your ears that will be the most telling variable. The best way to learn about these things is to get a piece of audio with a large dynamic range (very loud and very quiet points) and just play around with these settings to see what they do. 

Attack and Release

The attack setting on a compressor changes how quickly a signal becomes compressed, while the release setting changes how quickly the signal goes from being compressed to uncompressed.

A very fast attack time is up to around 800 us (microseconds), but too fast an attack time can also cause distortion. Slower attack times range from 10 to 100 ms (milliseconds) and means the start of a loud signal will still make it past the threshold because the compressor is slower to act. So, even after compressing you may notice large spikes of transients still visible in the audio.

Release times will usually range anywhere from 40-60 ms to 2-5 seconds. For podcasts, 0-100 ms would be short, 100-500 ms would be medium and 500+ ms would be long.

Knee, Makeup Gain, etc.

The knee is quite simple to understand. It hardens or softens the transition from uncompressed to compressed. A soft knee is a gradual transition, while a hard knee is relatively sudden.

To tie this all together, makeup gain can be used to bring the peaks of the compressed signal up to the same level as the peaks before they were compressed. This maintains the same peak level, while also increasing the levels of the entire piece of audio.

This gives you greater control when adjusting audio levels. If you were to increase the overall levels of your audio without adding any compression in an attempt to make the quieter points of the audio louder, the peaks of your audio might clip and the quieter parts will still be low in comparison to those peaks, and the only other option would be to commence some kind of strange balancing act within the recording where you might end up chopping and changing each minute shift in volume to balance out the levels.

So, as you can see, even though compressors can feel like a lot to take in and understand, with time, practice, patience and research they are an invaluable tool and, on the whole, are a small point of processing that really can make a massive difference to the audio quality of your podcast.


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