What Does an Audio Compressor Do? The Basics and How to Use It

A tool that is not new to those who have a lot of exposure to audio editing tools. But What Does an Audio Compressor Do?

by Derrick Reeves | Updated: October 11, 2021

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Ever wanted to know more about audio compression?

The answer is here! In this article, you will learn what an audio compressor does, how it works, and the basics of how to use one.

Audio compressors can be used in a variety of situations such as live performance, recording studio, or even just at home with your computer.

Once you understand what this piece of equipment can do for you and where it might come in handy, we'll go over some tips on how to use the best tools available to get started today!

What Are The Benefits Of Using A Compressor? What Does It Do?

A compressor makes soft parts louder so they're easier to hear and enjoy while still being able to compress loud portions without distortion or excessive noise (except when set at maximum settings)

Using compression on an entire album helps create dynamics that may otherwise be lacking in a group of songs that all have about the same volume level; this is especially important for pop music tracks since radio airplay formats require consistency between different song's volumes levels as well as between individual instruments within each song.

This type of consistent tone is what some people call "punch" or "bite".

Using compression on individual instruments - such as guitars, vocals, drums, and so forth - is often used to give them a denser sound while still being able to be heard clearly.

In the world of pop music, this can help make songs more exciting with faster tempos without sacrificing any clarity in the mix; it also helps rock bands that are trying not to include too much distortion for their heavier guitar parts by allowing these sounds to sit within an acceptable dynamic range.

A vocal can be affected using this, or it can be used in a recording as an extension to isolate louder sound sources (i.e. drum isolation). Studio and live recordings can both benefit from it.

What Is Audio Compression?

What Is Audio Compression

Audio compression is the process of reducing the dynamic range in an audio signal. This can be done to make quieter sounds louder and more audible or vice versa. A common use for this is when vocals are too quiet, so a compressor may bring them up as well as control any background noise that might drown out the vocalist's voice.

The Dynamic Range is the difference between the loudest sound and the quietest sound. Compression reduces volume levels of louder sounds by a certain threshold so that they do not overpower quieter ones.

Compressors are usually used to make softer passages audible or more dynamic, such as bringing up vocals in a song with very little instrumentation on some parts of the recording where the vocalist would otherwise be buried in background noise (background music).

It also can help producers create an overall fuller-sounding track, which is important for radio airplay formats like pop and rock because those types of songs have different requirements than instrumental compositions; while pure jazz may require less compression since it has fewer dynamics anyway.

The main job of an audio compressor is to even out differences in volume between various parts of a track.

This can make it easier to hear all quiet passages at any given moment and ensures that when loud moments come around you are able to discern them clearly over the rest of the soundscape.

That's not all! Audio compressors also have parameters like threshold control (which determines how much your signal must exceed what has been set before changes will occur), the attack time (the amount of milliseconds - or ms - until compression occurs once enough amplitude has passed through), and release time (how long compression continues after an increase in level).

Threshold

The "Threshold" is the point at which a compressor will start working. In other words, if you set your threshold low enough, then any audio that peaks below this level will be compressed.

If too much compression is applied - something known as overcompression or squashing - it can lead to what's called pumping and breathing effects in an audio mix; music with less dynamic range may also sound muffled. It might also change the timbre of individual instruments within a song (i.e., make them more similar).

Ratio

Ratio

The "ratio" is the ratio of input to output. It's a form of compression that multiplies or divides an audio signal, and it can be used in different ways depending on what you need out of a particular song. For example, if your goal is to compress just the bass drum without affecting any other instrument, you may set the input to a very low level and use a high ratio setting.

When the audio signal has been compressed, the compressor will output a compressed signal. This sounds different from the input signal and is more "squashed" - in a good way.

This parameter is usually represented as n:1 (1:1, 2:1, 3:1, 4:1....).

Ratio 1:1 is quite a special ratio because then the Compressor will do nothing, just let the signal pass.

Ratio 2:1 is a gentle compression ratio.

The ratio from 3:1 to 4:1 is a moderate compression ratio.

Ratio from 5:1 to 8:1 or more is a strong compression ratio.

The ratio from 10:1 or more up to ∞:1. The compressor is considered a limiter and does not allow signals to exceed the Threshold anymore.

Attack Time

The "attack time" is how quickly the compressor starts to work once a signal crosses over the threshold level. You can adjust this setting depending on what you want out of your song, and for example, if you're trying to lower levels in between lines of vocals or dialogue (i.e., lowering the volume when someone isn't singing), then an attack time that's low will be useful.

Release Time

An audio compressor also has a "release time," which determines how long it takes for sound levels to return back down after they cross below the threshold point again. This affects sustain as well - shorter release times mean sustained notes have more decay, while longer release times equate to shorter decays.

Auto Release Time: Changing this parameter can have dramatic effects on what you hear as it relates to how quickly the compressor kicks in and releases when signals reach the threshold.

Knee

The "knee" refers to how gradual the volume change is once it crosses over the threshold set by your compressor's threshold control. A soft knee (or hard knee) means that when sound levels cross above or below a certain point, they're immediately changed dramatically - this can be good for times where you want one explosive moment in an otherwise very mellow track.

Soft Knees: For instance, if you have a solo guitar performance and would like the loud passages to really stand out from those parts of the song where they are more subdued, then using a soft-knee setting will ensure that each transition has some dramatic effect on what listeners hear next. The same goes for vocal corrections.

Hard Knees: Alternatively, hard knees will result in less noticeable transitions, which may be better for a song where the instrumentation remains relatively constant throughout its duration. As its name suggests, Hard Knee will help the compressor work better with heavy sounds such as bass, drum sounds and percussion.

Basically, How Does An Audio Compressor Work?

How Does An Audio Compressor Work

An audio compressor also has a threshold level that it works off of: once a signal crosses over this point, the compression starts to kick in.

You can adjust how much you want your song compressed depending on what kind of sound you're going for - if you want loud, punchy drums or vocals then generally speaking you'll have a higher threshold than if you wanted softer ones with lots of subtleties in them. The setting where the attack time is long enough so that gain reduction doesn't happen until after some peaks come through means smoother levels overall.

A good rule of thumb when adjusting these parameters would be to start with the Attack at around 20 milliseconds and adjust from there.

You can also use a compressor as an auxiliary processor on any instrument or audio channel, not just vocals. An excellent example of this is to put it in front of guitar amps to smooth out the dynamics between playing soft and loud.

This way your levels will be more consistent for all parts of your song instead of having moments where everything's super quiet after something really loud happens. It should go without saying that you want to watch what kind of sound you're shooting for before doing anything like this!

Read More: What Is Bit Depth And Sample Rate In Audio?

Conclusion

Audio compressors are a great editing application, with them you will have a lot of ways to process the sound you create and enjoy it.

In this article, we have explained to you what an audio compressor does from a very basic level.

Hopefully, by sharing some basic knowledge, you will have a better understanding of how a Compressor functions and how it can enhance the existence of your music.

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