How Does An Audio Compressor Work?

A compressor is nothing more than an automatic volume control, that turns the sound down when it goes above a certain level.

A compressor works with a Threshold value. For example -12dB. Sound that comes above this value is compressed.

Sometimes this is a fixed point (hard knee). But often the compressor already works at a level below the threshold, and starts working harder and harder as the sound gets higher in level (soft knee).

The degree of compression is determined with Ratio.

The Ratio is expressed as a number, for example 2:1. The higher the first number, the harder the compressor works.

A ratio of 2: 1 means that a note that is 6dß above the threshold is turned down 3dß.

A basic Audio Compressor.

Attack and release indispensable for audio compressors #

On a audio compressor there are more buttons, such as Attack, Release and Gain.

  • With Attack you determine how fast the compressor works.
  • With Release you indicate how quickly the compressor jumps back to its original state.

For short sounds, such as drums, short attack and release times work best. The compressor works directly and you strengthen the attack of the sound. This makes drum sounds more punchy.

For longer sounds, like piano and violin, longer attack and release times work better. Then you leave the ‘snap’ untouched and compress the body of the sound. The part is now more present in the mix. And soft passages can be heard.

Makeup Gain compensates volume loss #

A compressor makes hard passages in sound softer. This makes the whole audio signal sound softer. You can compensate this with Makeup Gain.

Make sure the before and after sound are equally loud. Then you can easily AB-test. And judge whether compression really adds something to the sound.

Sidechain compression: a special form of compression #

Normally you use compression for individual sounds or mix buses. The compressor works directly.

You can also make compressors ‘listen’ to other signals. This happens a lot in electronic music and is called sidechain compression.

In sidechain compression, the compressor responds only when another signal commands it. For example, you can use a kick as input for the bass line.

When the kick sounds, the compressor compresses the bass line heavily. As a result, the kick always sounds clear.

When the sound of the kick ends, you hear the ‘uncompressed’ bass line. This way they never get in each other’s way and you get a pumping effect.

The difference between a compressor and a limiter #

A limiter is a variation of a compressor.

The ratio of a limiter is in theory oo:1 (infinity:1). Most mixers use it from a ratio of 10:1.

A ratio of oo: 1 (in combination with a very short attack time) means limiting: no signal can rise above the threshold.

A limiter allows you to make your music sound much louder, without audio clipping.

Limiting works well with hard genres of music, such as EDM, hardstyle and drum & bass. But it’s tempting to overdo it. Therefore, use limiters with caution.

More interesting articles about mixing:

Make Sounds Louder Without Clipping
How To Make Sounds Louder Without Clipping #

Do you want to make your music sound louder? Then audio clipping is something to take care of. This is how you avoid it.

How Loud Should I Master my Song for Spotify?
How Loud Should I Master my Songs for Spotify? #

Spotify normalizes audio that’s to soft or loud. But how do you know how loud your tracks are? And how loud should you master your songs for Spotify?

Sound bigger and better with the Fruity Compressor.
The Fruity Compressor Improves Your Music (And This Is How) #

With a compressor plug-in, you can reduce the dynamic range of audio. This makes your music sound louder and punchier. In this article, you’ll discover how to compress with the Fruity Compressor.

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