Compression can be a bit of a dark art. It takes some time to wrap one's head around how it works. But, even then, there is a whole world of opportunities for you to go deeper with your understanding of compression.
Despite the simplicity of this tool, there are countless ways to use it. Once you've wrapped your head around basic compression, you can start to use advanced compression techniques that give more control, new opportunities and ultimately better mixes.
In this tutorial you will learn three advanced compression techniques:
- serial compression
- sidechain compression, and
- parallel compression
Mastering these techniques is the next step to truly understanding compression and using it with precision.
Before you attempt to use these techniques in your own mixes, you need to have a solid understanding of compression. It’s important to walk before you run. But, if you are confident with a compressor already, read on.
More Dynamic Control With Serial Compression
One of the main reasons to use compression is to level out dynamics. By compressing the louder peaks, and then turning up the overall signal (thereby raising the volume of the quieter peaks), you are creating more dynamic consistency in the source.
The loud bits get quieter, the quieter bits get louder, and whatever you are working with becomes easier to place in the mixing and stays at a more constant level. With vocals in particular, this is important. You need the lead vocal to sit on top of the mix at all times. To achieve that, you need compression.
But many sources, like vocals, vary quite wildly in terms of volume. One second, the vocalist is whispering, or the bassist is playing a quiet high note, and the next second, the vocalist projects their voice, or the bassist starts digging in on a lower fret.
You need a lot of dynamic control in these situations. If you rely on one compressor to do this, you can quickly remove the life and energy from the source. With something like lead vocals, volume automation is required as well as compression.
But there is another compression technique that reduces the negative effects of heavy compression. I like to call this incremental compression, others refer to it as serial compression. Either way, the objective and result is the same.
By using multiple compressors in a row, rather than relying on just one compressor, you can apply heavy dynamic control without over-compressing the source.
Don’t get one compressor to do all the heavy lifting. Instead, use several compressors on the same channel, and allow each compressor to do its bit. Usually, using two or three compressors on the same channel is sufficient.
You can take this one step further. By using different settings on each compressor, you can achieve things that aren’t possible with one compressor alone.
Try using a faster attack time on the first compressor to catch the louder transients and reign them in. Then use a slower attack time on the second compressor to leave the transients in tact and instead apply more constant control without losing aggression.
Creating Space With Sidechain Compression
This technique was supposedly discovered by radio DJs, who wanted a way to automatically lower the volume of the music when they spoke over the top.
This was achieved by applying a compressor to the music, but using their voice as the trigger for the compressor, instead of the music.
So, the compressor clamps down on the music as it normally would. But instead of clamping down when the music gets loud, the compressor engages when the voice gets loud.
Although this initial discovery was relatively simple, we can use this technique in a number of incredibly useful ways when mixing. We can use sidechain compression in the exact same way as the radio DJs, but on a much smaller scale.
Here is my favourite way to use this technique...
If something is fighting the lead vocals for space in the mix, there are a number of things you can do. You could adjust the volume of the competing instrument, or use EQ to make sure they aren’t fighting for the same frequency space.
But in addition, you can also automatically lower the volume of the competing instrument to make room for the vocals using sidechain compression.
Let’s say the electric guitar is too overpowering. Apply a compressor to the guitar channel (make sure the compressor has a sidechain function), set up the lead vocal as the sidechain, and apply around 2dB of gain reduction to the guitar by tweaking the ratio and threshold.
The aim here is to dip the guitar slightly every time the vocal comes in. Use a fast attack and release time to make sure it gets out of the way quick. It’s subtle, but it’s an incredibly efficient way to create more room for the vocal.
You can take this further by bussing together any instruments that compete with the vocal (guitars, keys, snare, backing vocals etc.) and apply subtle sidechain compression to all of them at once on the buss. Very efficient.
Versatile Processing With Parallel Compression
This is another technique that appears simple but has a surprising range of incredibly powerful uses.
Parallel compression is the act of compressing a duplicate of the source, rather than compressing the source itself.
For example, you might send the vocal to a new buss channel, or just duplicate the channel and the audio. Then, you apply heavy compression to this new version of the vocal and tuck it in underneath the original vocal performance.
This way, the vocal never drops too low, and you have some dynamic control without affecting the original performance and dynamics. Instead, you are just raising the quieter words, rather than compressing the louder peaks - so the original performance sounds more natural.
In essence, this is a form of upward compression, rather than downward compression. You are bring up the volume of the quiet bits, rather than bringing down the volume of the louder bits.
Much like serial compression, this is a more musical way of applying heavy compression and dynamic control, without ruining the dynamics of the performance. Some mixers rely heavily on this technique, and rarely use direct compression.
In addition to using this technique on vocals, another common use case is to duplicate the drum buss, heavily compress the new version, and tuck it in underneath the drums.
Ensure you have a good understanding of compression before diving into these techniques. Then, once you start applying these three tricks in your mixes, you can achieve new things that aren’t possible with normal compression.
But don’t just use them for the sake of it. If you notice an issue in your mix that could be solved with one of these techniques, go for it.
Remember, every move you make should be intentional. Think of these as new tools for your toolbox, and you can’t go far wrong.
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