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What Is Compression In music? (Compression explained)

Beginners to mixing music often ask, what is compression in music?

It can be a hard concept to grasp when you’re first starting out so, in this video, I wanted to explain what compressors do in music by taking a step back and explaining the concept of compression and why we use it and then show a few basic examples on vocals, snare and kick drum.

This video is not so much about compressor settings but more about the mindset and concept of compression explained.

Compression Explained

It’s a tricky technique to grasp and can take a long time to master but by understanding what a compressor does to music, how it controls the dynamics and changes the tone, then we can apply it with more understanding and creativity.

Explaining compression is easy on the face of it, it’s a simple piece of equipment but understanding how we can use it in a musical way takes a little more practice.

If you're looking for my FREE download for vocal compression settings guide then you can find it HERE!

Video Transcription

Compression in music, what's that all about then? Today I'm going to start at the beginning and tell you the origins of compression and show you what it does, so you can get a better understanding of this wonderful thing called compression and why audio engineers keep banging on about it. Hi, I'm Sara Carter from simply mixing dotcom, where each week I bring you simple practical advice to help you get better at mixing. Now there are loads of tutorial videos out there on compression, some basic and some that go into more advanced techniques.

But in this video, I want to take a step back and explain where compression came from and why we need to get a really clear understanding of what it does and how it shapes sound. And while you're here, I'd love it if you'd like and share this video and don't forget to subscribe and then share your favorite compressor in the comments and how you like to use it in your mixes.

Now, I'm going to delve deeper into the nuts and bolts of compressor settings in another video, this video is more about your mindset and encouraging you to think about the sound you want the goal before slapping on a compressor plugin and randomly switching between presets without understanding what's happening under the hood. But if you can't wait until then, there's a link in the description for you to download my six step guide for compressing vocals like a pro. So what's a compressor and what they used for?

Well, their origins started in the 1930s and 40s when radio networks needed a way to control the audio signal in the latter part of the broadcast chain to prevent over modulation, which, to cut a long story short, can cause the transmitted signal to distort and possibly fail.

As an added bonus, it was later used by radio engineers to control the very dynamic audio levels created by different radio presenters, music and audiences as it reduced the need for engineers to be constantly riding the faders, or rotary faders in those days, to make audio easy to be reproduced on the radio at home without causing damage to the broadcasting equipment by accidentally clipping the signal. It pretty much became the standard tool in almost every recording studio. Engineers would use it to make their job of riding the faders on the console much easier and end up with more powerful recordings that translated better across different sound systems. So a compressor can be thought of as an automatic fader.

It's used to proportionally reduce the dynamics of a signal that rises above a predefined level known as the threshold. It's designed to keep levels consistent, that's it. To give you an example, I'm going to show you a vocal that has a lot of dynamic range or level changes.

Right then, so I've got a track here I just want to use to demonstrate the vocal to you. As you can see, when I talk about dynamic range, you can see it in the waveform on this particular audio track here. You can see that we get some sharp increases in volume throughout the performance and you've got lots of difference between the quieter parts and the louder parts of the signal. And this is the verse. And then as we get to the chorus, you can see things just get even crazier.

So let's see how a compressor handles these peaks in the waveform. We'll just take a listen to it as it is in solo.

OK, so you can hear the level, how the level is fluctuating throughout the performance, and sometimes this can happen because the singers are moving around, they're moving around the microphone. They might be gesturing as they sing because of the emotion involved in the lyrics.

It's just what singers do. And so that projects itself sometimes through the microphone and onto our recordings. Choruses tend to be louder than verses, of course. And then we also get this issue with comped vocals. So if you've got lots of vocal takes and you're chopping and changing between different takes, choosing the best bits to build up the perfect vocal take, then often this is where you can see these dynamics are taken to the extreme. Now, how do we treat this vocal?

Well, we've got the option of riding it by hand like those early radio engineers did. Or we can try using compression. Compression is a better option because usually if you're riding things by hand, you tend to miss things. You don't catch everything. So let's see what happens when we add a compressor to this track. I've got here a plugin, which is an emulation of a well-known compressor, which is the La2a. And what this compressor will do is we'll get to see in this display here how many dB's it is reducing from the original signal.

So let's just remind ourselves of this phrase here.

What it sounds like without compression

So this section here where she's singing about a righteous mess, that's where the audio level really jumps out at you. And it's exactly the type of signal that a compressor is able to grab hold of quicker than us humans and control them according to the settings that we've predetermined here. Let's switch this compressor on and see what it's doing.

So without.

So it's grabbing this peak here really nicely and controlling it, making it sound much more consistent, and that's going to be much easier for us to deal with in the course of a mix. It's only grabbing one and a half dBs but it does make an audible difference.

Then, of course, where we're going to see the greatest gains is when we go from a verse into a chorus. So let's see how the compressor handles that. So let's, let's hear a chorus first without the compressor engaged.

So this section of the vocal here was quite significantly quieter and would just simply get lost in amongst the arrangement of a chorus. Let's see again, see how many db's the compressor is able to help us control in this performance.

So you also noticed that this last phrase is more even, it's more level. It's the same sort of level range as the previous two phrases here. And that's, of course, what compression is all about. It's reducing the peak levels and then what you're able to do then when you bring the signal back up after the compressor has pulled it down, the net result is that the quieter sections of the song or vocal sound louder than they did originally. So you're reducing the dynamic range that is the difference between the quietest and the loudest parts of the performance.

So let's have another listen. Without.

So what else can you notice about this? There's also, apart from the obvious consistency now that we've got in the levels, there's also a change in tone. The quality of the vocal has changed for the sake of variation, let's have a listen to another section.

So what the compressor's bringing there is more depth. I can hear that there's, the vocal sounds a little fuller. It sounds as though the vocalist may be standing closer to the mic where, of course, you can get a bit of proximity effect. But that's not happened in this case. That's what the compressor has brought to the performance. So it's not just a case of levels, it's also the quality of the voice that will change the tone and thickness.

So compression does a better job of controlling levels than I ever could, and that's it's main function.

But what about that change in tone? This is a second reason why we use compression when mixing music. Different compressors offer different tones or flavors or vibe, call it what you will. Compressors can also be used to change the shape of a sound according to our needs, by having an idea in our head of what we want the source to sound like in the mix is the starting point and then we go about creating that sound using the compressor.

Let's take a snare drum, for example. The sound starts with the initial hit of the stick and we get that sharp peak in the waveform and then that dies away as it gets quieter and quieter.

Well, with a compressor, we can change that shape by using the attack and release controls. We can shave off the top of that initial peak and we can increase the sustain of the tail to smooth out each snare hit, if that's what we want. Let me show you what I mean.

OK, so thinking about compression on a snare drum, this is where we can really get creative and start changing the shape of a sound and what I'm going to show you here is just a couple of different sounds you can pull from a snare drum. Let's just think about this, though, for a second. Let's have a listen to the snare as it is. This is just a real snare drum in a room played by drummer, there are no samples here or anything, this is just the raw snare mic, so nothing fancy going on here.

There's a little bit of EQ just to try and enhance what I've got. But apart from that, it is what it is. So let's have a listen to the snare.

OK, so the first impressions for me are that the snare drum just sounds a little short, you hear the initial attack of the stick hitting the skin, but you don't really hear much in the way of the body of the drum or the snares themselves. So if I were to compress this to try and bring out those specifics, then let's look at this compressor here, which is the CLA76 by Waves, which is a very popular compressor, often used on snares.

So let's see what we can do with this.

OK, so that's definitely bringing up more of the body of the snare, I'm hearing more of the snares themselves and the length of the snare hit has increased. So you can just, it's just more present throughout the whole track. Now, what also has happened as well, is in bringing up the body of the snare, the quieter side of the snare, if you like, then that's also brought up spill on the microphone from everything else in the kit. So you can hear more cymbals and you can hear more kick drum.

That's something you've got to bear in mind and you can deal with by using things like a gate. But on the whole, I like that sound of the snare. I think it still sounds natural and it's enhanced it. So what about if we go to a different extreme and choose a different setting? Well, here I've got the same compressor, but it's a UA version and this sounds slightly different. Take a listen to this. It's really bringing up the ring of the snare and that's maybe what you're after, again, it's making that decision before you even put a compressor on.

What do you want the snare to sound like? And as we heard in my initial assessment, I just felt the snare was a little bit short and it just had no length to it at all. So that is what I would address first. And both of these compressors do that. They both lengthen it and they both bring up the snare sound. So I could happily use both of these. The first compressor, the first example is a bit more natural sounding, this one is quite aggressive.

So let's remind ourselves of the difference between the two.

Two different flavors of compression there, depending on what you want, and both examples bringing up more of the body of the snare, one brings out the ring a little bit more. So it's just decisions, really. What is it that you want? And of course, with everything like this, we're listening to these things in solo. But you'd ideally, you would do this whilst listening in context with the mix.

That's how you'd get the best settings. As always, listen to it in context of the mix. And by making decisions like this up front, then we're going to mix faster. We're not going to get lost in preset land and we're not going to second guess ourselves. So which one did you prefer?

And finally, one last demonstration for you. The kick drum, usually out of the kick drum, people are looking for more punch, definition, that chest thump, more power.

So let's have a listen to this and see what we've got from the kick drum in this particular session.

OK, it sounds quite soft to me, it also sounds slightly inconsistent. A kick drum, you want to be solid driving force through the song and this sounds as though the kick is just a little bit soft and some of the hits are quieter than others and so the level is fluctuating a little bit too much. We can use a compressor it to fix that and let's try out another 1176 and see what we can do with this.

Then with the compressor, I think that improves that slightly. Definitely improves the performance and makes it a little more consistent and it's got some more punch, hopefully you can see that it's not only level control, tone comes into it as well when you're using compressors.

So it all comes down to personal taste and what we feel is right for the track. So it becomes very difficult to answer the question of how to compress anything because the answer is, well, it depends. How do you want it to sound? Do you want the snare to sound spiky and short, or do you want to hear the delicate ghost notes that are getting lost in the mix? Both need a different approach and different compressor settings. Before reaching for a compressor, know why.

Decide what you want to do before you automatically add one, just because you think you should. Do you need to control dynamics?

Would you like to alter the transient of the sound somehow, or do you want to get creative and change its shape, smooth things out or sharpen things up?

Then you can have fun exploring the myriad of different flavors of compression out there and create the sound you want and not what a preset offers you. So that's all for this video.

And if you want to learn more about compressing vocals, then click the link below to download my 6 step guide, how to compress vocals like a pro.

Then consider subscribing and click the bell to get notified every time I release a new video. That's it for today. Thanks for watching and I'll see you in the next one.

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