Mastering Audio Compression: A Beginners Guide

Audio compression is an essential tool in music production that can help produce a more polished and cohesive sound. 

However, mastering the art of audio compression can be a daunting task, especially for beginners. With so many different types of compressors and settings to work with, it's easy to get lost in the technical jargon and end up with a sound that's less than optimal. 

In this blog, we'll provide you with a comprehensive guide to audio compression, including everything you need to know to get started, from the basics of compression to more advanced techniques used by professional sound engineers. 

Whether you're a beginner or a seasoned pro, this guide will help you take your audio compression skills to the next level and achieve the perfect sound for your music.

For a full overview of the tools you’ll need to get to grip with alongside compression, read our Beginners Guide To Music Production.

Audio compression refers to the process of reducing the dynamic range of an audio signal. In basic terms, audio compression involves lowering the volume of louder sounds and amplifying softer sounds, which creates a more consistent and balanced sound overall. 

The purpose of audio compression is to achieve a more even sound throughout a recording. It works by reducing the gap between the loudest and quietest parts of the audio. This can make the audio sound louder, clearer, and more polished. This makes audio compression an essential technique used in music production, podcasting, broadcasting, and many other audio applications.

There are several key controls in a compressor that are important to understand, including:

Using these controls, you can apply compression to different audio signals to achieve different effects. Threshold determines the point at which the compressor starts making changes to the audio signal. For example, if you set the threshold to -20dB, the compressor will only affect sounds louder than -20dB. Ratio controls how much compression will be applied to the audio signal, with higher ratios resulting in more compression. Attack Time determines how quickly the compressor engages, while Release Time controls how long it takes for the compressor to return from compressing the audio signal.

One really simple way to understand audio compression is to compare the process to packing a suitcase. Just like how you have a limited amount of space in a suitcase and need to fit as much as possible without exceeding the weight limit, audio compression involves fitting as much sound as possible into a limited dynamic range without exceeding the threshold.

In the same way you might fold your clothes or use packing cubes to fit more items into your suitcase, audio compression techniques such as threshold, ratio, attack, and release can be used to fit more sound into a limited dynamic range. Similarly, just like how you need to ensure that your suitcase isn't too heavy and exceeds the weight limit, you also need to ensure that your audio doesn't become too loud and distorted, exceeding the threshold level.

Here is an example of a sound without audio compression:

Now, here is the same sound with audio compression applied:

You'll notice that the version without audio compression sounded much flatter. The drums were not pumped as clearly throughout the synth sounds. Whereas, the version with audio compression decreased the synth's volume levels each time the  drum kicked in, helping the beat stand out and the synth flow around it.

There are a range of useful tools that every beginner music producer should get to grips with; equalisation (EQ), reverb and compression are just a few. While compression can be a useful tool, it should be used sparingly and with intention. Overuse of compression can lead to a loss of dynamics and a "squashed" sound.

As a general guide, here are some common scenarios where using compression can be beneficial:

1. To even out volume: compression can be used to even out the volume levels in your audio recordings. This means that parts of your recording that are too quiet can be boosted and parts that are too loud can be brought down, resulting in a more consistent overall volume level.
2. To add sustain to instruments: compression can be used to add sustain to instruments such as guitars or drums. When an instrument is compressed, the quieter parts of the sound are boosted, resulting in a longer sustain time for the notes.
3. To add punch to drums: compression can also be used to add punch to drums by bringing out the attack of the sound. This means that the initial impact of the drum hit will be emphasised, resulting in a more powerful and dynamic sound.‍
4. To glue together multiple tracks: compression can be used to "glue" multiple tracks together in a mix. When multiple tracks are compressed in a similar way, they can sound more cohesive and blend together better, resulting in a more polished and professional sounding mix.

Audio compression is a powerful tool in music production. But like any tool, it's important to understand how to use it properly. There are several parameters to consider when setting up a compressor, including threshold, ratio, attack time, and release time.

Threshold is a fundamental parameter in audio compression that controls the level at which the compressor begins to work. It determines the point at which the compressor will start to reduce the volume of the audio signal. Any signal that exceeds the threshold will compressed by the amount specified by the ratio control. For example, if the threshold is set to -10 dB and the ratio is set to 2:1, then any signal above -10 dB will be compressed by half (reduced by 6 dB), effectively bringing the level down to -13 dB.

The threshold setting is the starting point when using audio compression, because it determines how much of the audio signal will be affected by the compression.

If the threshold is set too high, only the loudest parts of the audio signal will be compressed, leaving the quieter parts untouched. If the threshold is set too low, the entire signal will be compressed, even the quietest parts. Therefore, it is crucial to set the threshold at the appropriate level to achieve the desired balance and consistency in the audio.

Tip: When you increase the threshold by setting it to lower dBs, it makes the compressor start working on more and more sounds in your audio. This can produce a more dramatic effect. To get a more subtle effect on your sound, set the threshold lower so that it's only affecting soft sounds.

Examples of threshold control in use

Here are some examples of how threshold control can be used in audio compression:

• Vocal processing: when compressing a vocal track, you may want to set the threshold so that the compressor only kicks in when the singer sings louder than a certain level. This can help keep the vocals at a consistent volume level throughout the song.
• Bass guitar compression: bass guitars often have a wide dynamic range, meaning that some notes may be much louder than others. By setting the threshold appropriately, you can ensure that the compressor only kicks in when the bass guitar reaches a certain level, keeping the overall level consistent.‍
• Drum bus compression: when compressing a drum bus, you can set the threshold so that the compressor only affects the loudest parts of the drums, such as the snare and kick drum. This can help bring out the attack of these instruments and make them punchier in the mix.

The ratio control determines how much compression will be applied to your audio signal once the threshold level is crossed. 

The ratio is expressed as a numerical value such as 2:1, 4:1, 8:1. The first number represents the input level, and the second number represents the output level.

For example, if you set the ratio at 2:1, then for every 2 dB of volume beyond the threshold, only 1 dB will make it through. If you set it at 4:1, then for every 4 dB units of volume beyond the threshold, only 1 dB will be allowed to pass through. This results in a more compressed sound, as the dynamic range is reduced.

A lower ratio such as 2:1 is suitable for subtle compression, while a higher ratio such as 8:1 or 10:1 is more appropriate for heavy compression.

It's important to note that the higher the ratio, the more drastic the effect on the audio signal will be. So it's recommended to start with a lower ratio and gradually increase it until the desired effect is achieved. If the ratio is too low, the sound will be compressed 100% of the time, which can result in an unnatural sound.

The graph below shows how the ratio affects the sound's output level (dB).

Examples of ratio control in use

Here are some examples of how ratio control can be used:

• Vocal compression: when recording vocals, it is important to keep the dynamics consistent throughout the performance. A ratio of around 2:1 or 3:1 can be used to achieve a natural sounding vocal performance without any sudden changes in volume.
• Drum compression: drums are one of the loudest instruments in a mix and can easily overpower other elements. Using a high ratio of around 8:1 or 10:1 can help to tame the drums and keep them under control.
• Bass guitar compression: bass guitar is another instrument that can easily get lost in a mix. A ratio of around 4:1 or 6:1 can help to even out the dynamics of the bass guitar and make it more present in the mix.
• Master bus compression: master bus compression is used to glue all the elements of a mix together and create a cohesive sound. A ratio of around 2:1 or 3:1 can be used to gently compress the entire mix and make it sound more polished.

Attack time determines how quickly the compressor starts to reduce the volume of a signal once it exceeds the threshold level. In other words, it controls how quickly the compressor "attacks" the incoming audio signal. This is measured in milliseconds (ms).

For instance, if your attack time is set to 15ms, the compressor will kick in following a 15ms delay whenever it detects sounds above your set threshold level.

A shorter attack time means that the compressor will start to reduce the volume almost immediately, while a longer attack time means that the compressor will wait longer before starting to reduce the volume.

The attack time setting is important because it can affect the character and dynamic range of the audio signal. A shorter attack time can result in a more aggressive and punchy sound, while a longer attack time can preserve more of the transient detail and natural dynamics of the audio signal.

It's worth noting that attack time is not always a critical parameter to adjust, and it depends on the type of instrument and the desired outcome. In some cases, a longer attack time can be more appropriate to preserve the natural dynamic range of the audio signal, while in other cases, a shorter attack time may be necessary to achieve a specific sound or to prevent certain parts of the audio signal from overwhelming the mix.

Examples of attack time in use

Here are a few examples of how attack time can be used in audio compression:

• Drums: a fast attack time can help to tame transient peaks in drum tracks, such as the initial hit of a snare drum. This can help to even out the overall level of the drums, making them sound more consistent and controlled. For aggressive drum tracks, you might want a fast attack time of around 10-30 ms. This allows the compressor to quickly react to the initial punch of the drum hit, which can be very loud and cause distortion if left unchecked.
• Vocals: a slower attack time can be used to preserve the natural dynamic range of the singer's performance. This can help to avoid squashing the peaks of the vocal performance and can lead to a more natural-sounding result. Attack times for vocals can vary depending on the style and genre of the music. For smooth, sustained vocal lines, a slower attack time around 50-100 ms can work well. This allows the initial transients of the vocal to pass through uncompressed, while still catching the sustain of the note. For more percussive, staccato vocal lines, a faster attack time around 10-30 ms might be needed to control the sharp peaks of the vocal.‍
• Bass: When compressing bass guitar or synth bass tracks, a medium attack time can be used to capture the initial "pluck" of the note while still allowing the sustain of the note to come through. This can help to keep the bass sound punchy and well-defined, while still allowing it to sit in the mix without taking up too much space. For example, an attack time of 30-50 ms can allow the initial attack of the bass note to pass through uncompressed, while still catching the sustain and any additional harmonics that might be present.

Here's an example of a sound compressed with fast attack:

Here is the same example sound compressed with a slower attack:

The release time refers to the amount of time it takes for the compressor to return to its original state after the audio signal has fallen below the threshold level. In other words, the release time is how long it takes your compressor to disengage with the input sound – this is the direct opposite of attack time.

The release time control on a compressor allows the user to adjust how quickly or slowly the compressor returns to its normal state. This is measured in milliseconds (ms) and can range from very short (less than 10ms) to very long (over 1 second).

A shorter release time means that the compressor will stop compressing the audio signal quickly, while a longer release time means that the compressor will take longer to release the audio signal back to its original state. Shorter release times are typically used for fast and percussive sounds like drums and longer release times are often used for sustained sounds like vocals, guitars or strings.

Too much release time can result in an overly compressed sound, and equally if your release time is too quick, your sound levels might not be compressed enough. 

As with attack time, there is no exact science when applying release time. The best way to determine how much attack and release time you'll need is to assess the audio by ear until it sounds natural.

Examples of release time in use

Here are some examples of how release time can be used in audio compression:

• Vocals: let's say you're compressing a vocal track and you want to create a smooth, consistent sound without any noticeable pumping or breathing. In this case, you might set a fairly fast attack time to catch the peaks, but then use a longer release time (say, around 200ms) to let the compressor release gradually and avoid any abrupt changes in level.
• Drums: for drums, you might want to use a faster release time to make the hits sound snappier and more pronounced. For example, you might set a release time of around 50ms for a snare drum track to help the hits cut through the mix.
• Bass guitar: with bass guitar, you might use a longer release time (say, 300ms) to help smooth out the dynamics and make the notes sustain more evenly. This can help prevent the bass from getting lost in the mix and ensure that it provides a solid foundation for the other instruments.
• Overall mix: finally, when compressing an entire mix, you might use a release time that's tailored to the tempo of the song. For example, if you have a slow ballad, you might use a longer release time (say, 500ms) to allow the compressor to respond more slowly and create a more relaxed, laid-back feel. Conversely, for a fast-paced dance track, you might use a shorter release time (say, 100ms) to help the compressor keep up with the rapid changes in level and maintain a consistent groove.

Yes, it is possible to use multiple compressors in a signal chain, and it is a common practice in music production. However, it is important to use them in a way that benefits the overall sound, rather than making it worse.

By using multiple compressors, you can take advantage of the different qualities of each one to achieve a desired effect. For example, you might use one compressor for its smooth sound and another for its aggressive attack.

One common way to use multiple compressors in a signal chain is to place them in series. This means that the output of one compressor feeds into the input of the next compressor. The advantage of using compressors in series is that each one can work on a different aspect of the sound. For example, the first compressor might focus on taming the peaks of the signal, while the second compressor might focus on bringing up the quieter elements.

Compression is not only useful for controlling dynamics, but it can also be used creatively to achieve unique effects in your audio recordings. Here are some ways you can experiment with compression to create interesting and unique sounds:

1. Pumping or breathing effect: by using a high ratio and fast attack/release times, you can create a pumping effect that accentuates the beat and rhythm of the music. This is often used in dance and electronic music.
2. Sustain enhancement: you can use a low ratio and a longer release time to create a sustained effect, which can help bring out the sustain of an instrument or vocal. This can be useful for creating ambient or atmospheric sounds.
3. Parallel compression: by blending a heavily compressed signal with the dry signal, you can create a thick and punchy sound without losing the dynamics of the original recording. This technique is often used in rock and pop music.
4. Sidechain compression: by using a sidechain signal to trigger the compressor, you can create a "ducking" effect, where the volume of one instrument is lowered when another instrument plays. This can be useful for creating space in a mix or emphasising a particular instrument.
5. Saturation/distortion: by using a compressor with high input gain, you can push the signal into saturation or distortion, which can create a gritty and distorted sound. This can be useful for creating distortion effects on guitars or adding character to drum sounds.

Conclusion

In conclusion, audio compression is an essential tool for any music producer, sound engineer or artist. By using threshold, ratio, attack time and release time, you can control the dynamic range of audio and make it sound more polished and professional. 

By following the steps in this beginner's guide, you can start experimenting with different settings and techniques to achieve your desired sound. Remember, practise makes perfect, and the more you use audio compression, the better you will become at mastering it. Plus, experimentation is key when it comes to using compression creatively. Don't be afraid to try out different settings and see what works best for your mix. Happy compressing!