What is a Compressor? Audio Compression for Beginners


Thales Matos


Want to know what a compressor is — and how it works — so you can make professional-sounding music? Well, you've come to the right place.

And since audio compression is such an enormous subject, I figured it's better to break it down into a series of posts — a mini-course — instead of trying to tackle everything in one super long video.

This is Audio Compression For Beginners, Episode One.

ableton live stock compressor

Today you'll know, once and for all, what compression is and why it's so crucial for making music, especially pop music.

Once you understand that, you will use them all the time.

There are many ways to use compressors for different purposes, and they have a cool background story.

But we're going to keep it simple and objective, as always.

What is a compressor? Examples of audio compression

Before I explain, listen to the examples in the video above.

This is a guitar track before compression:

Uncompressed guitar waveform

And this is the same guitar track after some compression:

Compressed guitar waveform

Could you hear the difference? Did you notice what's going on with the dynamics?

What are compressors and what is their purpose?

Compressors are devices, hardware, or software, that even out the volume level of any audio.

They reduce the dynamics of an audio source.

It's like when you are watching a movie and have to turn the volume up during the talking scenes — then lower it during the action so the explosions don't freak your dog out.

That means taking audio that has a lot of volume variation — it goes from loud to quiet to loud again — and squeezing it to reduce the difference between the loudest signal and the quietest signal.

The loudness is going to stay more consistent throughout the whole audio. That's the main purpose of a compressor.

What happens if I mix without compression?

If an instrument or vocal track has too much variation in volume between phrases or even words, it can sometimes disappear in the mix.

The impression we get when we hear vocals that are not properly compressed on a pop song, for example, is that the vocals sometimes get buried in the back of the mix.

It's like they're in the background — they're quieter than everything else, you can barely hear them and understand the words.

Then all of a sudden, the singer starts singing with more intensity and now you feel like the vocals are too loud, and in your face.

And they keep going back and forth, between too quiet and too loud. That gets distracting and kills the clarity.

The benefits of compressing audio

With a compressor, we can make the loud parts of the vocal track sound quieter, allowing us to bring the volume of the entire vocal track up.

So the quiet parts can be heard too — this brings out more details and everything becomes balanced.

That's why most pop music uses heavy compression. The level balance between vocals, guitars, synthesizers, drums, and bass stays consistent.

And that's done on an individual track level — for instance, you can compress the vocals, bass, and guitars individually.

vocal compressor

This is the CLA-2A by Waves, one of my favorite compressors for vocals

Or you can compress groups of instruments — even the whole mix — to glue them together so nothing stands out beyond the levels you intended.

parallel compression, drums group, glue compressor

Then the whole song stays in a certain dynamic range or loudness range.

How much Compression in Classical music vs. Pop music

If you listen to classical music, you'll notice that oftentimes there are huge variations in loudness.

classical music dynamics

The whole orchestra will get super quiet at some point, then suddenly "BAM!": now it's very loud, and composers use this to create a cool effect.

So classical music has a lot more dynamics than pop.

That doesn't mean compression is a bad thing.

It just creates a different sound, and that's a matter of taste.

Even classical music producers and audio engineers use compressors sometimes. Just not to the same degree as pop music.

If pop music had the same dynamics as classical music, you would be listening to a song on the radio, in your car, then suddenly you wouldn't hear the song anymore, because the traffic noise would mask it in the quiet sections.

You probably wouldn't remember the chorus or even like the song.

It wouldn't be as commercially viable as it would if they had used more compression.

I even used a compressor in the video above to make sure you can hear my voice when I speak softly.

what is a compressor and how it works

How to use a compressor

Every compressor is built differently, but a very basic compressor only needs two controls.

That's actually all you need, for now, to understand how it works — even though they usually have a lot more controls.

A basic compressor needs a Threshold control and a Ratio control.

basic compressor controls threshold and ratio

The Threshold control

Whenever the compressor detects audio peaks that go over a certain level that you choose — the threshold — it will squeeze the signal that goes over that threshold by an amount also chosen by you, through the ratio control.

Threshold: how loud the signal has to be in order to trigger the compressor — or the level at which compression starts happening.

This means compression doesn't happen unless the audio level goes above the threshold you chose.

threshold control, izotope neutron compressor

The Ratio control

The Ratio control tells the compressor how much to reduce the audio that goes above the threshold.

For example, if your ratio is 2 to 1, half of the signal above the threshold will be taken away.

compressor ratio - compression explained

Beware. With compressors, a little goes a long way.

What is Overcompression

Sometimes if you use too much compression, you can squeeze the life out of the audio.

That's called overcompression, which makes your song loud but lifeless. In the video above you can find an example of overcompression.

Did you notice how flat it sounds? That's what happens when you go too far with your compressor.

What's next

In the next episodes, we'll go deeper into the compressor controls and how to use them in your songs.

We'll talk about techniques like parallel compression, multiband compression and sidechaining. 

Also, every single creative technique I've learned on this subject over the years so you can make great songs with excellent dynamics using this great tool.

Click here to read the Next Episode: What are Threshold and Ratio on a Compressor?.

If you have any questions, let me know in the comment section below.

For more music production tutorials, visit my website.


Thales Matos

August 21, 2022


Enjoyed this article ?



Leave a Comment

{"email":"Email address invalid","url":"Website address invalid","required":"Required field missing"}