There is no shortage of ways to process your audio using compression. Compressors are one of the most powerful tools when it comes to building a balanced mix, which has led many engineers to experiment with processing sounds with more than one compressor on a single audio track.

This method is called serial compression, and while it may sound intimidating, it's fairly easy to understand once you get down to the basic principles. Below, we'll dive deep into everything you need to know about serial compression and its use cases so that you can use this renowned technique in your own audio-processing workflow.

What is Serial Compression?

Serial compression means utilizing multiple compressors to shape and tone your sound on your signal chain. It's a form of serial processing, where compressors are stacked in a particular order to create the desired polished sound.

Let's consider an example. Say you have a vocal track that has an uncompressed signal that needs a bit of gain reduction and warmth in order to fit in the mix. Chances are, you're going to need more than one compressor. The first compressor in your signal chain, focused on gain reduction, will have a fairly hard-hitting threshold in order to tame the peaks of your sound.

The second compressor, may have a more subtle effect, with a low threshold to add the tiniest bit of compression while coloring your sound. When stacking compressors, order matters. The original signal moves through each processor, with each level of processing building on top of the layer beneath it.

In short, serial compression is the act of stacking multiple compressors within one audio track or bus chain. Using serial compression can give you greater control than if you were to opt for a single compressor:

Why Should You Use More Than One Compressor On the Same Track?

If you choose to use serial processing, you should have solid reasoning behind it since this effect can quickly become overpowering when not approached delicately. Here are the key reasons why you might use multiple compressors to compress tracks in your music:

Tone

Each compressor has its own timbre characteristics. This could also be described as the sound color, distinguished with words like "warm" to describe a more vintage sound, or clean to describe a more modern compressor. The best way to understand the tone of your compressor is to put it on an unprocessed audio track and bypass the compressor on and off without changing the threshold, attack and release settings.

Listen in to see how the compressor shapes the tone of your sound. Some compressors are more subtle than others, but this is a good way to get to know your compressor toolkit so that you can effectively process your mixes.

Timing

Perhaps you find yourself wanting to process different tones of your sound at different speeds. You might set a multiband compressor as a slower compressor to shape the highs with a slow attack, and then layer another multiband compressor focused on the lows with a fast attack. Serial compression gives you room to process your track across the frequency spectrum with varied timing.

Control

Layering compressors provide ample space to fine-tune and adjust your chain according to taste. However, it's easy to overwhelm a mix with too much processing, so make sure each compressor you add has a distinct quality it is actively adding to your chain. Consider the order of your processing as well - processing designed to clean up your sound should come first, while creative or tone-shaping effects should come later in your chain since every processor or compressor in this case is additive.

Remember that there are several alternatives to serial compression. For instance, you might try using a single compressor, sidechain compression , or try parallel compression (sometimes called New York compression) to achieve your goal. Remember that each added processor and addition to your mix should have a key purpose - the route you get to building a great mix doesn't matter as much as the reasoning behind your engineering workflow.

Serial Compression Versus Parallel Compression

It's easy to confuse serial compression and parallel compression, as the two compression processing methods both provide additional control around shaping your sound as opposed to opting for a single compressor. The main difference? Separation.

Serial compression by nature is contained within a single track or audio bus where compressors are actively stacked on top of one another inside of the contained space. Parallel compression deliberately separates the uncompressed signal and compressed signal onto separate tracks, creating a controlled blend of the two signals.

You could use serial compression within parallel compression, or blend an unprocessed vocal track with a processed vocal track with multiple stacked compressors. Each method has its own merits and sound so it's a good idea to try out both, or a combination of the two methods to shape your sound in the way you'd like.

What is Serial Compression Used For?

There is a reason why there are so many different types of compressors and methods for applying audio compression to your mix. As outlined above, each compressor comes with its own set of characteristics in terms of tone, purpose, and functionality based on its design.

Serial compression gives you the opportunity to stack these effects, without having to rely on one compressor alone. It can also help you dial in your processing, without squashing the audio signal. You may find that subtle adjustments delivered across a stacked compression chain provide more natural results than a single compressor with a high ratio of compression.

Serial compression is more or less catered to personal preference, but it's common to see this method in action on drums, vocals, and live instruments that might bring in a high dynamic range. By opting for serial compression, you have additional control over the shape of your processing, but remember that stacking compressors can easily lead to an overly squashed signal. It's all about creating a balance between polished processing and preserving the dynamic integrity of the original recording.

How to Use Serial Compression

If you're ready to start putting serial compression to good use, use these tips to effectively guide you through the process:

Clean Up Comes First

As with any audio process, subtractive processing, or processing concerned with cleaning up your sound should come first. You might want to start with an FET compressor, for example, to tame the peaks or dynamic range of your source material. FETs are known for being fast, reactive, and powerful to clean up the more obvious hiccups in your track. Everything builds off of the prior processing of the chain, so start by making sure you have a clean slate to build upon.

Switch to Optical

Next, you might add an optical compressor for a smoother feel on some of your transients. You might start your serial processing with harsher compressors to catch larger hiccups, but your audio should feel fairly consistent once you've finished processing - consider tools like optical compressors to give you a more gradual effect overall.

Coloring Compressors

You can then move onto compressors with a little more color character like a tube compressor or glue compressor which is modeled after an 80s mixing console if desired. These compressors will serve to add a bit more warmth or vibrance to your mix.

Use Limiting Compressors Last

Make sure that anything used to amplify your sound comes last in your chain. A limiting compressor should enhance an already well-shaped sound based on your previous nodes of processing.

Check Your Chain

When working through a complicated serial processing chain, it's easy to get lost in the process. As a best practice, bypass each compressor individually across your chain to double-check that each compressor is serving its intended purpose. If you find that one compressor isn't providing the effect you hoped or has changed since switching up your signal chain, it's time to reconsider or cut out that processor entirely.

There is no need to add unnecessary processing to your audio and checking your chain will ensure that you're only adding what you truly need to your signal chain.

Serial Compression FAQ

Are you still hoping to pin down the ins and outs of serial compression? Here are some commonly asked questions answers that will help you have a stronger understanding as an audio engineer:

What is serial compression?

Serial compression is the act of using multiple compressors in a sequence to produce a desired effect in your signal chain. Each compressor in a serial compression chain serves a different purpose. For instance, when using two compressors in your chain, one compressor might be used for its ability to tame transients, while another is coloring the sound with warmth.

What is the difference between parallel and serial compression?

Serial compression involves layering several compressors on top of one another within a single signal chain. Parallel compression involves blending a clean and compressed signal by placing a compressor on a send track or audio bus.

Where should you use serial compression?

Serial compression is ideal for instances where you need more than one compressor to tone and shape the sound of a single track. This technique is most commonly used on vocals and drums, or any other track that has a wide dynamic range.

In short, serial compression is an excellent technique to give you more control over the shape and tone of your sound. There are endless ways to set up a series of compressors on a signal chain, so be sure to test out different methods as you see fit. The only rule is that each compressor should serve a distinct purpose in your signal chain. Have fun using this engineering technique to get the most out of your mix!