Audio compression allows you to limit the dynamic range of an input signal.
If that went over your head, imagine the vast volume difference between a vocal singing softly versus really belting it out.
Compression allows you to bring the two closer together by reducing the level of the loudest moments.
I’ll show you how to use a compressor. But first, you need to understand all the different settings. So, let’s go over each.
Attack sets the speed at which the compressor activates after the signal crosses the threshold.
So, a slower attack time will allow the beginning of the signal to pass through untouched before applying the compressor, whereas a fast attack time will apply the compressor almost immediately.
Release sets the speed at which the compressor ‘lets go’ once the signal goes back under the threshold.
A release time that is too short can produce a choppy or jittery sound, whereas a release time that is too long can result in a signal sounding ‘squashed’.
Gain allows you to restore the signal back to its original level before compression. So, if you are compressing the signal by 6dB, you can apply 6dB of gain to bring the signal back to where it was.
In essence, this increases the loudness of the uncompressed signal by 6dB while keeping the compressed signal where it was to begin with.
Threshold determines when the compressor kicks in. So, if a threshold is set to -30dB, the compressor will start working when the signal gets louder than -30dB.
Ratio determines how much compression is applied. For example, if the ratio is set to 4:1, every 4dB of signal that crosses the threshold will be compressed down to 1dB.
So, if the signal crossed the threshold by 8dB, only a 2dB increase would be heard. Only two more settings to talk about, so hang with me.
The knee setting determines how the compressor responds once the signal crosses the threshold.
A hard knee clamps down right away, while a soft knee causes the compressor to gradually kick in as the signal gets further past the threshold.
Next is the compressor type. You have two options: RMS and Peak. Peak compression will be more thorough, compressing everything that crosses over the threshold, whereas RMS compression will be a bit more tolerant and therefore less noticeable.
So, if you want compression to be noticeable, use Peak. If you want it to be more transparent, use RMS.
Now, let’s talk about the Side Chain. This enables you to fine-tune what exactly triggers the gate to open. Self Keyed refers to the same signal you are working on.
You can also set the compressor to activate based on another signal. There’s even the ability to set a certain frequency placement that triggers the compressor.
The last compressor setting on this mixer is the Parallel path. This enables you to mix the uncompressed signal with the compressed signal. Dry refers to the uncompressed signal. Wet refers to the compressed signal.
In the audio world, this is referred to as parallel compression. It is a common technique used to hit the sweet spot of a controlled, yet life-filled sound.
Well, just like any other audio processing, never use compression just because it is available. Use it to solve a problem – otherwise, leave it alone. With that being said, I recommend using compression on every vocal channel.
Vocals have a wide dynamic range – they can sing really soft or really belt it out. A compressor takes this wide range of volume and makes it as narrow as you want it to be.
But, keep in mind, dynamic range on a vocal is good, so you do not want to cut it too much, you simply want to make it manageable.
In other words, you want to be able to bring them to the front of the mix while not having to worry about their ‘power note’ making everyone in the room cover their ears.
There are settings on the compressor that will be the same for every vocal, so let’s go over those first.
Now, there is one setting that you will have to dial in for each vocalist, and that is the threshold. You’ll want to set this while the vocalist is really singing out, so the best time is while they are practicing with the band.
Because, if you single them out to sing by themselves, they aren’t going to sing the same as they will with the band playing.
So, while they are singing out, adjust the threshold using the gain reduction meter. This is that little red meter on the compressor settings screen.
You’ll want to adjust the threshold so it reads around the same place where the green meets the yellow on the gain level meter.
During the quiet moments, it may not register at all, and that’s okay. You just want it to be compressing the vocal down about 6dB whenever they are really singing out.
Keep in mind, if you compress more than 6dB, the vocal starts to sound lifeless and smashed. So, if you start to notice the vocal losing its shine, the first place to check is the compressor.
This is actually something you want to check on a regular basis because you never know when a vocalist might find their confidence, or maybe a different person starts using the microphone.
When this happens, adjust gain first like we talked about in the video about gain. And then adjust the threshold on your compressor so that it doesn’t compress more than 6dB.
Now you know how to use a compressor on vocals. You’ll also need it on some of your instruments, so I’ve included a compressor settings cheat sheet in this course to give you a head start.
This is only 1 lesson from our SQ Mastery Course. Check out the full course here.
