What Does an Audio Compressor do?


An audio compressor plays a key role in making sure your recordings are close as possible to the 0-decibel level. For best results, however, it may sometimes be necessary to tweak the equalization settings as well.

For example, if you are trying to enhance the sound of a kick drum but your crash cymbal is louder, for compression, the peak amplitude will be set by the crash cymbal. Ideally, you would simply lower the crash cymbal’s high frequencies and increase the kick drum’s lower frequencies.

Back in the day, compressors used to cost quite a bit and ‘riding the faders’ was certainly the default technique for most home studio owners. However, after using a compressor, you’ll realize that it is much quicker than a real person could ever be.

A fader needs to be operated manually, you have to know exactly where a recording becomes loud or quiet. It’s impossible to do this without playing the track through and memorizing it all the way – without that, you will never be able to move the fader in time and respond too late. The compressor, on the other hand, knows exactly when to adjust because it identifies level problems in real-time. 

However, a compressor does not have the intuition or feel that a musician does. It only does what it is programmed to do. This is why you need to understand how the output is affected by the variable parameters.

Keep in mind that the compressor ‘listens’ to the recording electronically by monitoring the signal levels – that’s how it reacts faster than the human ear. The side chain (a part of the compressor’s circuit) modulates the gain control by monitoring the highs and lows. When the signal level rises above the maximum, the side chain generates a control signal to reduce the gain and vice versa. 

Parameters of Compression

So far, you should have a good idea about the purpose of compression. But how does this translate practically? What are the different parameters you could control using a compressor, and how can you use them to achieve the sound you want? let us break down the different knobs you could find on a compressor to answer those questions.


The threshold determines the signal level atwhich your compressor starts functioning. The measurement for threshold is always in decibels (dB). So, any signal that exceeds your preset threshold dB gets compressed. The threshold you set determines the signal levels that will be attenuated.

Setting a low threshold will generally make your compressor attenuate a bigger part of your signal. On the other hand, having a higher threshold will only affect your signal’s peaks.

To find the proper threshold, you should first determine what you want to achieve by compressing and what portions of your signalto target.


Ratio is the amount of gain reduction that your compressor applies whenever a signal exceeds your preset threshold. As the name implies, the ratio is expressed relative to the uncompressed signal. Essentially, the ratio’s first number determines how much the voltage gain is reduced, where a higher first number results in a higher gain reduction. You’ll see ratio settings in between the 1.5:1 and 10:1 range are most utilized.

A high first number in your ratio will result in an abrupt flattening effect. On the other hand, a lower number will result in a gentle compression which you can usually apply to your entire mix. To find the best ratio, set the threshold at a specific range, then vary the ratio knob to see how it affects your sound. As you are increasing the ratio, listen closely to when the attenuation effect becomes noticeable.  Stop whenever your audio starts to sound squashy.

Attack and Release

The timing on your compressor determines when the compressor’s gain reduction begins and stops acting on your signal. You can control the timing using 2 parameters, Attack (begin) and Release (stop).

At this point, you are aware that whenever a signal exceeds your threshold, your compressor will start reducing the gain depending on your set ratio. In contrast, attack and release controls determine HOW your signal gets attenuated.

Essentially, Attack and Release controls determine whether the compressor achieves maximum gain reduction gradually or immediately. This makes them the most significant parameter if you are looking to achieve a natural sounding compression. Set a fast release and you risk an artificial pumping effect. Set a fast attack and your transients will get squashed.

Usually, you should have a firm idea of what parts of your audio must remain dynamic. You then set your timing controls accordingly. You can achieve the best compressionby planning out what type processing each of your sounds needs.


You probably won’t find knee control on a lot of compressors. Since it isn’t as common as the other controls, it’s generally not as important. However, this doesn’t mean that a knee control is useless. Plus, you might just be curious about its functionality.

The knee controls the nature of the gain reduction applied to an audio. It has a value ranging between 0.0 and 1.0. where a 0.0 value stands for a hard knee and a 1.0 value stands for a soft knee. A soft knee means that the gain reduction occurs gradually whenever the signal nears the threshold. A hard knee, on the other hand, means that the gain reduction occurs abruptly after the signal crosses the threshold

The knee control has a more subtle effect on audio than attack and release controls. Still, it can be very valuable at times. Generally, go for a soft knee accompanied by slow attack and release times if you are aiming for gentle compression. Otherwise, you can go for a hard knee with fast attack and release times in order to achieve aggressive compression.

Make up gain

Compression is often associated getting a track to sound louder. Yet, up until this point, we defined compressors as devices that attenuate audio signals. Essentially, it is the make-up gain control that allows you to increase your track’s loudness. Using this control, you can make up for any lost levels. And since you already compressed the aggressive peaks, you can increase your overall audio levels without any clipping.

How to Improve your Audio with Compression?

You can couple compression with EQ to remove any excess sibilance, which are unpleasant high frequency sounds that have a hissing quality. Using a compressor, you can target specific high frequencies in vocals (mainly around the 5kHz-8kHz range) to get rid of any excess sibilance. You can control WHICH frequencies get affected by setting your compressor’s threshold.

Additionally, you can use a compressor for noise filtering. If you are recording in a crowded setting, then you would want to block some of the background noise. As such, you can use a compressor to only allow your voice’s frequency to pass through. You can do this by blocking any frequencies below your compressor’s threshold.

This way, any part of your audio with no speaking voice will not have any background noise.  And any parts with a voice will probably be loud enough that the noise gets inaudible. You can find several uses for compressors, but those are the most common.

Can Compression Ruin a Recording?

If you’re not careful, you can definitely ruin your mix by misusing a compressor. One of the most common things that people do with a compressor is overusing it! If you assign extreme values to your knee, threshold and timing controls, your audio will definitely be ruined. You should be very precise with your control values.

Another effect of misusing a compressor is pumping. That is your audio gets louder and lower in an extremely unnatural way.

It’s ironic that both of those negative effects are the result of compression, even though a compressor is used to fix such issues. Once a music amateur learns about compression, they will undoubtedly fall in love with it. And I don’t blame them a bit for that, compression is fantastic! However, as an over-joyous novice this love is often expressed in the form of over-compression. So, take it easy. Be very moderate with your compression.

Another way people misuse compression to ruin an audio is by killing its variations. This is particularly common when it comes to music, which is meant to have gentle and loud portions. That’s pretty much the aim of most music. The way the intensity falls off then rises as the story progresses is what gives music its beauty. You need to have varying intensities in your songs.

By over-compressing, your song can end up sounding very monotone. Without the rise and fall in intensity, your song will be sucked out of life. Not only that, it can also become very dull and unpleasant to listen to.

It’s completely up to you to experiment and decide whether flattening your song’s intensity is worth the compromise in overall volume. Different strokes appeal to different folks.

Final Words

Be cautious! Compression could be as dangerous as it is beautiful. It’s very easy to find yourself sucked up over-compressing the hell out of everything!  But this will only make your songs sound crappy. As a beginner, you should put a lot of hours into testing to learn how each parameter affects your mix. This process is certainly tedious and time-consuming. But eventually, you will reap the rewards when you can achieve any sound you want using a compressor.