What Is Audio Compression?

Audio compression, or sound compression is basically compressing the peaks in your dynamic range to allow you to bring up the other elements in your track. The dynamic range is the space between the top and bottom lines of the waveform display. Audio compression will help you keep your sound waves within this area. When an audio signal is too hot, meaning too strong it will leave the boundaries of the top and bottom lines causing what is known as clipping. Any sound that passes outside of the top and bottom lines is clipped off. You will not hear the audio, but instead more of a click noise. You can think of compression as a way of compacting the strength of the audio signal.

Dynamic Range Picture

Audio Compression can be used to avoid clipping and help bring out the quieter sounds in the track. So how is this achieved? Rather simply once you understand sound compression. FL Studio offers several different audio compression options, for now though I will just focus on the basic Fruity Compressor.

Fruity Compressor

On the Fruity Compressor you have 6 knobs. The first is threshold. What this knob allows you to do is set the audio level where you want the compressor to start working. The db value of the knob is the same as the db value in your audio meter.  Lets say you set it to -10db. That means any sound signal under -10db will be unaffected while any signal that is stronger than -10db will be compressed. This is when the rest of the knobs settings will come into play.

You can think of ratio as the main control of audio compression. This is how you set the amount of compression applied to any signals that pass above your threshold. All of the ratios start with one number then have a 1 as the second. The first number is the one you change to control the amount of compression.  A compression of 6:1 means if the audio signal goes 6db above your threshold then it will come out of the compressor sounding like it only gained 1db.

Lets say you set your audio compressor to have a threshold of -10db and a ratio of 4:1. what will happen here is every sound signal that  is stronger than -10b will be reduced. If the signal would go to -6 db without compression then it will now only go to -9db with 4:1 compression. The higher the first number the more your audio will be compressed after threshold.

Compression VS. No CompressionThe ratio is the hardest part of audio compression to understand. Once you get a grasp of what the ratio does the other controls make much more sense. The gain knob is pretty self explanatory. The higher you set it, the more strength your output signal will gain. Gain is what is use to bring out the weaker sound signals while compression will reduce the stronger ones. By reducing some of the audio signal peaks you clear up more dynamic range to use for gain, which makes your overall sound signal stronger.

Attack and release work at the opposite ends of the audio compression threshold. Attack is how quickly the the compression ramps up to full after the threshold is passed. Release is how quickly the the compression stops once the sound signal drops under the threshold. By setting a longer attack time you will allow more of the audio you are trying to compress to reach its full strength before the compression is applied and the signal is reduced.

Thy type which is also called knee in many sound compressors sets how smoothly the compressor will kick in when an audio signal nears the threshold. If you want instant compression once the threshold is reached then a hard knee will do that. Soft knees will allow the audio compression to change gradually when the audio signal is around the threshold.

Ways you can use compression.

Compression Peak ViewNow that you hopefully have a little more understanding of how audio compression works I will show you some of the ways you can put it to use. Lets say you want a loud bassline but the drum you are using has a very strong initial attack. You can compress the first part of the drum hit then bring up the level of the majority of the bass sound with the gain.

Perhaps you have a guitar track that you would like to even out a little. You can add some compression and gain to achieve this as well. A good time to use compression is while you are making the song or during the mixdown phase. Apply the compression to the individual instrument track that you want to change. With any compression you want to be sure that the sound produced is what you are looking for. Too much compression can lead to a pumping sound, or the audio level jumping up and down rapidly. Unless this is something you want you will have to adjust the compression and other settings to give you a more natural sound.

The object is to apply your heaviest compression to each individual audio track that needs it, so when you master all you are really doing is bringing up the overall gain and maybe a little compression. By adding the heavier compression to just the tracks that need it such as a drum track, you will avoid having to compress everything in the master phase and possibly getting a “muddy” sound. You want each individual track to be balanced as a whole before you begin mastering.

Compression With GainIf one of the instruments you compressed is now louder than the others bring down its volume on the mixer to a level that fits the rest of the song. Then once everything is where you want it you can add the gain to bring everything up at once and should have little need to compress much.

Audio compressors are definitely a tool with many uses and applications. They also come in multiband
where you can add compression to different frequency ranges. I will cover these types of audio compressors later. Overall the best way to really learn is through experimentation and experience. Take some time to master this powerful part of audio production. You won’t be sorry that you did.

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One Response to What Is Audio Compression?

  1. Anonymous says:

    Good stuff. I dont know why people dont comment. I did and I think this will help me :) THX