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How and Why to Use Serial Compression

Dec 13, 2023

Does using two compressors on a single source sound like overkill to you? With a technique called serial compression, that’s exactly what you’ll be doing. Learn how to use this secret weapon when tackling very dynamic, tricky-to-control sources such as vocals, piano, and guitar.

How and Why to Use Serial Compression

Despite often having very similar controls, and very similar purposes, different compressors can have very different characters. Broadly speaking, we might separate these into ‘transient’ compressors that act fast and transparently to tame peaks and improve headroom, without affecting the sound too much, and ‘character’ compressors that push, pull and pump the sound to give it that special mojo often associated with analog hardware.

Both types of compression are useful, of course, and as it turns out, there are occasions when using both at the same time – one after the other – can be a powerful technique for controlling a tricky source. Serial compression is a very useful technique for processing piano, guitar and the human voice (singing or speaking).

Example Comps

What Is Serial Compression?

When we turn to a serial compression technique, we use two compressors on a source instead of one. One compressor is added to work on only the highest peaks, taming a signal’s extreme dynamics and increasing the available signal headroom. The other compressor is then used to add character and perform more ‘broad-brush’ compression duties.

Our first, transparent compressor, will be set with a high threshold, a high ratio, and fast attack and release times; the second, character compressor, will be set with a lower threshold, a lower ratio, and slow attack and release time.

Without us first reducing the extreme dynamic peaks of the signal with the first compressor, the second compressor would have to work harder and wouldn’t be as effective at its job of adding character to the signal.

Working with Problematic Sources

This guitar line comes straight from a DI’ed signal, fresh and unprocessed.

Guitar RAW

The audio is very dynamic, as expected from an organic raw guitar recording. Just by looking at the waveform, we can see the loudest parts are peaking very high, and the quieter parts are comparatively very low. Although this is an indicator of a healthy recording, it’s not going to translate well into a mix.

Extreme differences in dynamics like this present us with a perfect opportunity to use serial compression. Sure, you could go down the route of applying a single compressor, and it might yield the desired results, however, it would leave you having to decide between using a fast acting compressor (sacrificing warmth and character) or a slow one (sacrificing the overall dynamic range reduction).

When used effectively, serial compression will give you the benefits of both compression types, without losing any sound quality. Now, let’s take a look at how fast and slow-acting compressors independently alter the audio’s signal.

Guitar R-Comp FAST

In the above example, we’ve applied our faithful Renaissance Compressor (R-Comp) with the Attack set to the quickest setting - for R-Comp that’s 0.50ms (anywhere between 0.10-1ms can be considered a fast attack) and the Release to 50ms (a release range of 20-150 milliseconds could be considered fast for a compressor).

We’ve also set the Ratio to 8:1 to demonstrate an aggressive, and fast-acting transient compression, but don’t be afraid to go for a higher ratio if it sounds right. You can see and hear how the dynamics have significantly changed when compared to the original unprocessed recording.

Here’s a screenshot of our R-Comp settings for the first example.

R-Comp FAST

Because R-Comp is designed to be applied in varied circumstances, we’ve also used it with slower Attack and Release settings (Attack: 100ms, Release: 350ms), as well as a milder compression ratio (4:1) to demonstrate how a slow-acting compression type can alter the signal’s dynamics in a smoother fashion, leaving some of the transients unscathed. Anything above 10ms for a compressor’s attack, and a release between 200-500ms, could be considered slow.

Guitar R-Comp SLOW

In this second example, notice how the integrity of the original dynamics remains somewhat intact, however, you can still hear the warm tonal character that the compression has applied. See our R-Comp settings for the second example below.

R-Comp SLOW

Controlling Very Dynamic Sources with Serial Compression

Now, let’s move onto the fun part: combining both compression types to reveal the potential of serial compression!

It’s important to understand that, when combining these two compression types, both compressors’ settings need to be adjusted fairly precisely in order for them to complement each other. It can be easy to over-compress your signal and completely deteriorate the sound.

But we’ll be guiding you carefully through the process here with a couple of top-notch, analog-emulated compressors from our catalog that are ideal for each role. Remember, get experimental, familiarize yourself with the different types of compressors and their settings, and most of all, have fun!

You can pick up the compressors we’ll be demonstrating, plus many more legendary analog-emulated essentials from our online store. Otherwise, follow along with your own selections.

CLA-76 01

To set up our serial compression for best results, we want to choose two optimal compressors for each role (one slow and one fast). For our fast-acting compressor, we’ve opted for the CLA-76 - A precise digital emulation of a classic FET compressor, known for its rapid attack times, with a signature aggressive dynamic reduction. See the image above for the settings we’ve applied.

Here’s how it affected the waveform. You can see that it tamed a lot of those pesky high-peaking transients and evened out the overall dynamics.

CLA-76 Waveform

Now, let’s see if we can really help this guitar sample reach its full potential when we combine the CLA-76 processing with the Puigchild 670 Compressor - A meticulously-refined emulation of the legendary analog Fairchild 670 tube compressor. This compressor is famous for its vibrant polish, often used to apply warm glue compression in the mastering chain.

The main control of the Puigchild 670 we’re going to be focusing on is the Time Constant. This controls the attack and release times of the compressor – both of which are permanently linked when using this lively plugin. We’ve set our Time Constant to five, which ensures a reasonably slow-acting compression. You can also adjust the Input Gain, Threshold, and Output Gain accordingly.

Also, be sure to keep your middle dial set to Linked, to control both stereo channels using one set of controls. That is, unless you want to compress your left and right channels separately - one of the perks of the Puigchild 670. Check out our tweaked settings below.

Puigchild 670

There’s a night-and-day difference when comparing the before and after of having this additional character compressor applied. Which you can visualize in the image below. When looking at the waveform, we can see that the Puigchild 670 has beefed up the lower-level transients, whilst further evening out the peaks – all without jeopardizing the range, previously processed by the CLA-76.

SC Waveform

And there you have it! We’ve successfully combined two compression types to optimize the dynamics of our guitar sample. You can see and hear the increased thickness and warmth of the audio signal - something that would not be possible to replicate using a single compressor.

More Serial Compression Tips

Swap the Compressors’ Order

The compressors’ order can be swapped – try placing the transparent, peak-reducing compressor second, with the character compressor first in the chain. It won’t always work but can be worth a try.

Check out the resulting waveform and audio of our example with both compressors flipped below. Notice anything different? Better or worse? Perhaps it's personal preference!

SC Waveform

Serial Compression vs. Knee Control

Technically, a wide knee setting gives similar advantages to serial compression, letting you compress with a higher ratio the louder a signal gets. While this will get you part of the way, the knee setting on your compressor will unlikely have an effect on the attack and release timing of different amplitude signals.

Adding Even More Stages

For vocal and spoken-word production, or any situation where you have to get extremely pristine results, you can add more, intermediate stages of compression to a serial chain. Your first compressor could simply be a limiter, scalping the topmost peaks; the second could use a transparent compressor to improve headroom; the third to ‘level’ the signal on average and the fourth to add character.

There’s no limitations (only limiters). You just need to use each compressor intently, and keep a keen ear to exactly how you’re altering the signal.

Example Comps 02

Final Thoughts

Ultimately, serial compression is a fairly advanced engineering technique, and it’ll take some practice and getting to know the ins-and-outs of different compressors before you can maximize its creative uses. For now though, we hope to have set you on the right path for getting started.

If you’re looking to expand your compressor library and want to jump right into hands-on learning, there are plenty of compressor options to choose from in the Waves catalog. With just a couple of compressors and the right approach, you can take control of your transients and achieve a sturdier sound.

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