The Basics of Using Compression

So far in this series, we have covered a couple of basics in running sound. We first covered setting your gain structure. Then we covered some basics on EQ. And of course, these all go back to episode 0123 of the podcast.

Today we’re going to cover the highly useful, yet misunderstood topic of compression. It took me quite a while to get a good understanding of what compression is, what all the controls of compression do and how to use it. I say that in hopes that you will cut yourself some slack in learning this. It’s not that it’s extremely complex. It’s just new, and it can take a while to get used to some of the ideas.

It is what the title sounds like. You’re taking the sound and compressing it. Funny story, the first time I heard about compression was from a guy who had been running sound for some charismatic churches. They used compression and limiting on the mic that people used for testimonies. That way when people shouted into the microphone it wouldn’t blow everyone away. And that’s how compression and limiting work. They take the signal and compress the loudest parts.

I’m sure there’s a much more technical definition to it than that, but I don’t really know it. And I don’t really want to get technical since I’m trying to explain this in a way that a commoner can understand.

There are a few conrols that you’ll need to know when it comes to compression. The ones we’re going to concern ourselves with for this post are Threshold, Ratio, Knee and makeup gain. There are other controls such as attack and release, but let’s not go there yet.

Threshold is the point at which the compressor starts kicking in. It will usually have -db markings for you to guage how much you are turning the knob. It starts at 0 and goes down. At 0db, the signal isn’t being compressed. If you turn the knob down, you’ll notice the sound starts to get compressed. You should have a meter that will show you just how much, but it should be a different color than your channel strip meter lights.

Ratio is how hard the compressor compresses the sounds that go above the point you set the Threshold. For instance, if you have a 2:1 ratio, this means that for every 2db of sound that come in only 1 will go out. Or it will be compressed by 50%. 4:1 – 4 db in only 1 out, or compressed by 75%. You get the idea.

Knee is important because it is where the subtly of compression lies. If you have a hard knee, it could potentially be very noticeable when the compressor kicks in. If you have a soft knee, it will ease in and ease out. If you have a digital board, you might see a graph that has a line that goes up and to the right. It will have a bend it in where the threshold is set. The angle will change/bend to the right at that point. That is the knee. If shows a hard angle, you have a hard knee set. If it’s got a rounded angle, soft knee.

Makeup Gain is there to help compensate for how much you turn the highs down with the compressor. If you really compress something, chances are you’ll have to crank up the makeup gain to get it back to a useable level in your mix.

Now, how do we use all this? If you have a digital board, I would probably suggest using compression on pretty much every channel. (Once you have a good understanding of how to use it.) The reason is, it makes a big difference in getting things to sit right in the mix. When the levels are really drasting and constantly changing, it can be hard to get a decent mix. So, we use compression to make things a little more manageable.

Don’t go overboard, but don’t go underboard. You don’t want to overly compress everything, as doing so will suck all the dynamic and life out of the music. But, you also want your compressor to be active.

Here are a few basics I use. I generally try to have the compressor bringing down the level by about -6db. Some big peaks might be over that, but generally in that area. So, I’ll grab the threshold knob and turn it down until it’s coming down to -6. Then, I’ll mess with the ratio knob, I usually go somewhere between 2:1 and 8:1. if you’re going to go to 8:1, you might as well just put a limiter on the channel, as that’s almost what you’re doing at that point.

Compression can be great for performers who aren’t super consistent in the level. For instance, if you have a vocalist who sings really quietly on the verses, but then really belts it out on the chorus – compression. Bringing the loudest part down will keep you from having to ride the fade the whole song.

If you have an acoustic guitarist who will be fingerpicking on the verses, but then be in a full-on strum for the chorus – compression. That way you can bring the overall volume of the guitar up making it possible to hear the finger-picking, but then not be killed by the strumming.

For a Bass guitar, I like to add quite a bit of compression. This is more of a personal thing, but since the bass note is so foundational to the mix, I don’t want it to go away on quiet parts. So, if the bassist doesn’t have a compression pedal, I help him out with that.

Compression, just like EQ has thousands of different uses, and there are thousands of different theories on how to use it. These are just a few of the ways that I’ve come to use it as it applies to us. If you have other input, feel free to add it in the comments section.