Parallel Compression Explained

Parallel Compression Explained - What is Parallel Compression

Compression is vital to every great mix. However, an over compressed signal can leave a track feeling flat and lacking energy. Luckily for us, parallel compression allows for the best of both worlds: Ear pleasing levels while preserving the integrity of the sound.

In this article, we’ll get down to the nitty-gritty of using parallel compression properly.

Here is Parallel Compression explained.

What is a Compressor?

Softube Summit Audio TLA-100 Compressor
The Softube Summit Audio TLA-100 Compressor, read about it here.

Before diving into the more advanced world of parallel compression, let’s start with the basics.

A compressor at its core is any device that alters the outlier volumes of a signal in order to produce a sound at an overall more level volume.

For example, if a singer were to record a phrase with one note louder than the others, a compressor would reduce the volume of this note so that it sounds more cohesive as a phrase. In addition, compressors can be used to raise the volume of signals that are significantly lower than the average volume of a track.

In short…

… a compressor alters the amplitude of a signal to bring volumes closer to the average volume of the track.

Compressor Parts and Functions

Within each compressor, there are a couple of settings that an engineer can toggle to alter the sound. Every compressor can be broken down into a couple of main components:

Threshold – This part tells the compressor at what point or amplitude it should begin to compress. If we set a compressor with a threshold at -3 dB, only parts of the signal that are at or above -3 dB will be reduced in volume. The threshold tells us when to begin compressing.

Ratio – The ratio is how much compression is applied to the signal. A higher ratio means that more compression is applied to the signal once surpassing the threshold. Tracks with a greater dynamic range would require a higher ratio, as the compressor would need to compress more intensely to level out the overall volume. A 4:1 ratio compressor would apply more compression to a signal than a 2:1 ratio.

Attack – The attack is how quickly the compressor reduces or heightens a signal. A faster attack means the compressor will reduce volume immediately, whereas with a slower attack, the transition will be more gradual.

Release – The release tells the compressor how quickly it should stop compressing. Somewhat of a converse to the attack, a fast release means that the compression will stop almost instantaneously, whereas a slow release fades the compression out more slowly.

These basic parts allow for each mixer to have more control over their tracks, and create more polished sounds in post production, even if the levels of the pre-recorded tracks are extremely dynamic. Ideally, compression is considered preemptively even during the recording process.

To learn more about the theory of audio compression, read our previous article on this subject.

What is Parallel Compression?

Although regular compression allows for more control, an overcompressed signal can inadvertently destroy the magic of dynamics. The good news? We don’t have to pick between the two!

Parallel compression is a type of compression where by we place compression on an external send track, allowing the user to create a mixture of the dry signal (the audio signal without any dynamic changes made to it), and the compressed signal (coming from the send track). The combination of the compressed and uncompressed signals gives the listener a more level sound that’s less obviously compressed. When done correctly, parallel compression retains the body and feeling of a sound, while still sounding professional.

How to use Parallel Compression

1 – Set up send track

Begin by setting up a send track as a separate bus in the DAW of your choice. It is important that this is setup as send track, as we will be routing the audio files (or sending the signals) we want compressed to it.

To learn more about signal routing, read this article.

2 – Compress the send track

Place a compressor of your choice on the new send track and adjust settings according to the signal you are looking to compress. For example, if we are looking to compress a vocal, we will set the threshold right below the level of where the volume begins peaking, so that when we transmit the vocal track to our send, the compressor will know where to begin leveling out the volumes. Adjust the attack, release, and ratio accordingly.

Read more about how to compress vocals, using compression on bass, and compressing drums,

Send the desired track to compression send and adjust to your liking.

3 – Mix your wet and dry signals

Since the compression is on a send, we are able to effectively blend the compressed signal and the raw, dynamic version of the sound. Raise the send level slowly and listen for the sweet spot- When your track sounds ready, keep that send level. Be sure to listen in context with all sections of a track: A specific parallel compression setting may work in some areas effectively, and not at all in others. Keep your ears alert and have fun experimenting!

That’s it, we’ve officially parallel compressed like a studio pro!

Don’t get too excited, like any effect, it’s important to not overuse parallel compression. The best engineers are able to discern when a mix needs that extra boost, and where to apply it. That being said, let’s go over some common applications of parallel compression.

Common Uses of Parallel Compression

Vocals – Probably the most common application, parallel compression is often used to create standout vocals that are not overbearing. Since the voice is such a dynamic and versatile instrument, it makes sense that parallel compression would be needed here.

Drums – Adding regular compression to every drum file can ruin the dynamic groove of a track. Parallel compression of drums individually, or even percussion groups, can give certain signals the punch they need, while maintaining a reasonable level in a track.

Subtle Compression – In general, parallel compression can be used on any track to give it a more polished feel, while allowing backing vocals, keys, other instruments, etc. to still sound natural. Parallel compression can add a degree of complexity for the listener without being too obvious.

Above all, parallel compression gives us more control as engineers. Much like standard compression, it allows for songs to sound put together, but also grants the fluid, natural sound, that our ears love. With more options to craft a sound, the musical opportunities are endless. Give parallel compression a try on your next mix!

If you’re interested in the best compressor plugins by application, take a look at these posts.