What is it? How and When Do You Use it?
Welcome to Trevor’s Audio Master class. I will be your guide to the wonderful world of Compression. The definition of a compressor is, “An audio signal processing operation that reduces the volume of loud sounds or amplifies quiet sounds, thus reducing or compressing an audio signal's dynamic range.” I’m sure that cleared up any confusion on compressors. Any questions??
Ok, but seriously. These are questions that we often get when we are doing sound training. What is a compressor? How do you use it? When should you use it?
So, let’s dive into an explanation on them, so you can better know what they are and how to use them.
A compressor, in its most basic form, takes an audio signal and when the signal reaches a certain volume or amplitude, it reduces the volume or amplitude by a specific amount. A compressor also has the ability to add gain after compression essentially making the quiet signals louder and the louder signals quieter. I like to call it, “Shrinking the box of sound”.
Back in the analog sound board day, this operation had to be accomplished by an outboard piece of gear. Now, any newer digital sound console you come across will have the ability to have a compressor on each individual channel.
Most compressors you will be able to find on a digital sound board these days will have a few different adjustment options. Let’s look at a couple of definitions so we are on the same page.
~ Threshold: This is the input level when surpassed that the compression will kick in
~ Ratio: The compression ratio determines how much gain reduction the compressor applies when the signal passes the threshold level. For example, a ratio of 4:1 means that for every 4 dB the signal rises above the threshold, the compressor will increase the output by 1 dB
~ Attack: This is how quickly the compressor engages when the threshold is surpassed
~ Release: This is how long it takes for the compressor to stop working after the threshold is no longer surpassed
~ Knee: This is the slope at which compression is taking place. Hard=Immediate, Soft= More Gradual
~ Make Up gain: If you are losing gain in your compression this is where you can “re-add” gain to keep your gain structure the same.
Now I know what you are thinking, “But Trevor, how do I actually apply these tools to make my mix sound crisp?”
Well, I’m glad you asked. Over the next few weeks, we’ll be dropping more practical tips and tricks! Now, I may reference specific settings, but I can’t stress this enough: Listen for yourself, and ask, “Does it sound better?” and tweak and adjust to your taste. These are just going to be starting places for you, but it’s you who ultimately get to decide how your end product sounds.
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