This is part three of our audio compression series, where we will share with you the different types of audio compression techniques used in audio production.
Make sure to read the previous post on the common types of audio compressors for a better understanding of compression.
Audio compression is one of the most used tools in music production today. Audio engineers use different types of compression techniques when mixing to get the sound that they want.
Each audio compression techniques enhances the mix in different ways. Below are some common compression techniques and how you can use them when mixing.
Types Of Audio Compression Techniques
Parallel compression is an incrediable tool used by the pro mix engineers to get big powerful mixes.
This compression technique is every easy to set up and get your head around. Once learned, it can help you get better mixes.
In short, parallel compression combines the original uncompressed (or lightly compressed) audio with a heavily compressed version of the same signal.
Heavy compression, can cause artefacts that you may not need in the mix or even destroy the sonic quality of the audio (crushing the life out of the transient peaks).
With parallel compression, you keep the sonic integrity of the audio (all the transient are intact), whilst still benefit from the compressed signal (low parts of the audio are louder).
The result is a huge punchy signal with more presence. A dull vocal or drums can benefit from parallel compression.
When To Use Parallel Compression
If after EQing and compressing the vocal but it still lacks presence that a lead instrument should have parallel compression can bring it up front and centre in the mix.
Simple bus the vocal to an auxiliary track insert a compressor with a high ratio and lower the threshold until you are getting at least 20dB of gain reduction. Try and get a lot of gain reduction, the more the better.
You can use any compressor for parallel technique, but a compressor that doesn’t generate distortion when applying a lot of gain reduction is best.
Attack and release settings will depend on the audio signal getting compressed.
The parallel vocal transient peaks will get so drastically because of the amount of gain reduction applied.
When blended with the original signal, it will be practically none existence in the mix as the transients from the original audio is dominant.
The quit signal that didn’t get compressed will be identical to the quit signal in the original audio.
And when two similar signals are combined, the level is 6dB louder than each individual signal.
The way you have a nice full vocal with all the lows increased, but still have the transient peaks intact.
Parallel compression not only for vocals and drums but works on guitars, bass and even the master bus.
Essentially, sidechain compression is a technique where the compressor is triggered or controlled by an external signal source instead of the audio getting compressed.
This compression technique is also known as ‘ducking’ because whenever the triggered track plays the track that has the compressor ‘ducks’ or compressed to make room for it.
Sidechain compression used a lot in electronic music as an effect that gives the kick drum that pumping sound.
In mixing it is mostly used to create space and prevent frequency clash between instruments that are in the same frequency range.
A common example is the bass and the kick drum. Often time large bass tracks with long tails can overpower the low-end burying the kick whenever it is playing.
Sidechaining the kick to the bass track compresses the bass every time the kick plays allowing it to cut through the mix better.
Another application is to use sidechain compression to bring the lead vocal upfront and centre in the mix.
Most often the lead guitar or backing vocals can mask the lead vocal as they all live in the same frequency range.
Inserting a sidechain compressor on these tracks and set the sidechain to the lead vocal will bring down their levels anytime the lead vocal plays.
How To Sidechain A Compressor
The first thing to understand is that you will need a compressor that supports sidechaining before you can get started.
Depending on your DAW the process is quite straight forward. In Logic Pro X it is simple as inserting the compression on the track you wish to compress. Then assigning the trigger track to the compressor’s sidechain input.
In a DAW like Pro Tools, you will first send the trigger track to an auxiliary track and assign the compressor’s sidechain input to that aux.
Just like in normal compression process, the threshold, attack and release determine the amount of compression.
If you remember how compression works, you already have half the understanding of multiband compression.
Just like normal compressors, it reduces the dynamic range of an audio signal.
But instead of reducing the dynamic range of the entire audio signal, multiband compression compresses specific frequency ranges.
Each frequency bands on the compressor have controls specifically for that band. Threshold, ratio, attack, release, makeup gain, knee and they work in the same way as other compressors.
How to Use a Multiband Compressor
Multiband compression can quickly kill the mix. So it is important to know what you are trying to achieve before using one.
There are two ways mix engineers use multiband, to control dynamic range and to control frequency issues.
Controlling the dynamic range is the same as when using a regular compressor but for a specific frequency range.
Let’s say the drum bus mix sounds good except that the low end could be tighter.
But when using a regular compressor loud high-frequency sounds, such as hi-hats and cymbals that you don’t want to be affected also get compressed.
Using multiband compressor, you can compress frequencies 200Hz and below to control the kick without affecting other sounds.
Mix engineers use multiband compression to correct frequency issues because it has less effect on the sound’s sonic quality.
When using the EQ process to cut hash frequency, neighbouring frequencies also get cut. This can change the timbre of the audio.
Instead of removing these hash frequencies, multiband compressor allows you to turn them down without affecting other frequencies.
Although multiband compression is mostly used to process the master bus and sub-mix, there’s no reason not to try it on individual tracks. Just make sure you know why you are using it.