How to Hear Compression: Ear Training Guide

It can take serious time to hear how compression affects audio. We fast-track that process with the ultimate training guide for your ears – learn exactly what to listen for when using compression!

By Will Vance, Hyperbits

Seeing as it's one of the foundational tools engineers or producers use in their projects, one would think that learning how to hear compression would be an easy thing to understand. Unfortunately, that couldn't be further from the truth.

In fact, knowing exactly how to hear compression is usually a quality only seen in incredibly seasoned mixers. Coming to a comprehensive and holistic understanding of compression can only happen over years of practice and hundreds (if not thousands) of mixes. It can take even longer when mixers don't set aside the time to attune their ears to the minute changes in dynamics, coloration and movement a compressor can introduce to a signal.

Here we’ll provide you with a straightforward framework for training your ears to hear compression. But first, a little background.

Why Compression is So Hard to Hear

The majority of newer engineers tend to add compression just for the sake of it – because they've heard or read that it's something they should do. As an instructor at the Hyperbits Masterclass, I've come to see a misunderstanding of compression as one of the biggest hurdles our students learn to overcome. If you find yourself a part of this silent majority, don't be hard on yourself, there are myriad reasons why compression is so damn hard to hear, and many of these reasons are entirely out of our control.

The first is because we are all human beings. As such, we have a hard time recognizing the minor fluctuations in volume between two or three decibels (at least to the "untrained" ear). That is fine when you want to squash a bassline synth or distort a guitar, but untrained ears attempting to dial the nuanced decibel range needed for vocal compression will be fighting an uphill battle.

This is because our ears act as natural compressors, exponentially reducing volume the louder it gets. Nerves and muscles throughout your inner ear react to incoming sounds and vibrations, which help clamp down these high-pressure signals. The louder the noise, the more our ear "compresses" it, which makes mixing at low volumes even more vital.

The final reason is a bit more technical but lies in the fact that every compressor affects the sound in noticeably different ways. You can place digital EQs (like Waves Q10 or the Renaissance Equalizer) on a channel and expect near-similar results, but the same cannot be said with compressors. Some compressors control dynamics with surgical precision, where others offer more fluid compression that is almost musical. Some compressor plugins are transparent in design as to be felt and not heard, while others introduce desirable distortion and coloration to the sound.

This is why many top engineers have dozens of compressors (both hardware and software) in their studios. This is a double-edged sword, as each compressor's superpower lies in the unique ways they each do their thing, but it also means that your ears must become trained to many different compressors before you understand how each is controlling the sound.

The best forms of practice come through consistent repetition, so let's talk about one proven framework that makes learning how to hear compression simple, easy and replicable.

A Beginner's Guide to Hearing Compression

With all of the above in mind, let's talk about how you can start attuning your ears to hear the fast and minute changes in dynamics that a compressor introduces. Below, we have outlined a proven method to start training your ears to hear compression in just four easy steps.

Once you have a basic idea of how this framework plays out, you can start utilizing it to hear the three primary things compressors control:

• Dynamics
• Coloration
• Depth in the mix

Step 1: Load a Sample

Load a sample into your digital audio workstation (DAW). Recordings and samples with a reasonably snappy transient and a weighty decay/sustain work best, as it gives the compressor plenty of information to react to and enough sonic material to shape and alter with the compressor.

Snare sample

Pro Tip: I'd recommend starting with drums when learning to hear compression – specifically, single drum hits. The sharp transients and varying sustains of percussive hits make hearing the dynamics as they change that much more apparent.

Step 2: Load your Compressor

Now it's time to load up your plugins. As stated above, every compressor is different, so you'll want to reach for one that positively squashes the signal (you do not want this compressor to be invisible or transparent). At the Hyperbits, we all prefer using the Waves API 2500 for this exact reason.

Waves API 2500

Pro Tip: Some producers find that using another analog emulation plugin such as CLA-2A or the CLA-76 can be helpful here. This is because analog emulations colorize and distort the signal more so than sterile, digital compressors. This coloration can help accentuate the applied compression, making it even easier to identify when the compressor is being activated and applied. But it's a double-edged sword, as the coloration that the compressor introduces can distract and mask the actual changes in the dynamics. Try a few different models and see which works best for you!

Step 3: Set Aggressive Parameters

Now set the compressor's parameters to be as aggressive as possible. I'm talking infinite ratios, lowest possible thresholds, incredibly fast attacks and fairly long release settings. These drastic settings make the compressor's effect appear incredibly obvious, even to the most untrained ear. We will be easing up on these settings later on, but for now, make sure you’re looking to squash the signal into oblivion.

Waves API 2500

Pro Tip: Set up a keymapping that allows for rapid bypassing of the compressor. This allows you to quickly A/B test. The above audio was recorded using this tip, which allows you to hear how easy comparing the signal can be.

Step 4: Look and Listen

When you're just beginning to train your ears to recognize compression, it can help have a visual representation of how the compression affects the audio. Here is a simple list of steps you can do in almost any DAW that will help guide both your eyes and your ears.

1. Beneath the channel that has your signal that is being compressed, create a blank audio track.
2. Route the audio of the compressed signed to this empty channel.
3. Hit record, hit play, and begin adjusting the parameters on the compressor, starting at the most extreme settings.
4. Watch waveforms of the sampled audio channels in response to the compressor's adjustments.

The above waveform is the uncompressed snare; the below waveform is the snare after compression.

Think of this step like training wheels, and once your ears can instinctively hear the applied compression, you may not need this extra piece. But until that day arrives, it helps to have a visual accompaniment.

Now it's time to start using this framework to train your ears to hear compression.

What to Listen for When Compressing

The above framework allows your ears to hear noticeable changes in the sound and help you identify the three primary and aforementioned ways a compressor affects a song. Each will require you to listen to slightly different things as you work your way through the process.

Listening For Dynamics

A compressor offers two solutions when controlling the dynamics of a signal. One is to bring up the volume of the softer nuances of a signal, heightening the musicality of a performance by adding density and power through compression. The second applies a downward squeeze on the track's loudest moments, taming peak levels and avoiding overloading and clipping the signal.

Start by listening to the above clip, which uses samples from a free Hyperbits Sample Pack, and pay particular attention to the breath, reverb and space between the vocal phrases.

Now it's time for you to try applying the above framework to the same loop, heavy-handed at first but slowly easing up on the effect, to a loop of your own. What do you hear? The below audio shows the starting point of the frame, where the same vocal loop is squashed into oblivion.

As you work your way through the framework, your eyes and ears should notice some key differences. The most obvious should be that the tail-end breaths and expressions suddenly become louder. Does what you hear change when using different loops? What do you hear when using the framework on a vocal or woodwind compared to a recorded drum performance? The denser breath and emotion of saxophones and vocal loops might add emotion and power to the loop, whereas the tone and noise of the room in a drum recording might make the percussions seem larger than life.

The example below shows the compressor sweeping through its settings on the same vocal loop. Hear how the background reverbs and breaths are full and present due to the compression. While the compressor may be reducing the overall gain of the signal, the evenness of the RMS leads to a more prominent vocal loop.

The less obvious thing you may not hear but will undoubtedly see if you're printing the practice exercise to audio is that the peaks of the recordings will be clamped down. If you want to train your ears specifically to begin hearing the taming of loud peaks, you will want to set the attack on your compressor, giving your ears plenty of time to listen to the compressor responding to the peaks of the signal.

Keep in mind, most loops from sample packs are already heavily processed, so do what you can to find unprocessed recordings.

Listening For Coloration

Every different hardware compressor unit is built entirely differently, and the various electrical components used in each model will color the sound in different ways. Some may add weight and punch to the mid-range frequencies, while others add a bright and aggressive fuzz to the top end.

When training your ears to recognize the subtle differences in the tone and coloration that compressors introduce to a signal, it is best to use plugins modeled after these hardware compressors, such as the CLA-2A or the CLA-76. Digital compressors can offer transparent compression, but that's not what we're after here.

When training your ears to hear the coloration of a compressor, I recommend using a relatively dense guitar loop. It provides a lot of sonic material for the compressor to interact with and color, and can give a fairly constant coloration when the signal is squashed, but more sporadic coloration as the compressor's settings are eased up upon. In example 7a below, the compressor is bypassed, and in example 7b the compression is activated – revealing added bite to the upper mids of the guitar while also squashing its dynamic range (especially when the higher notes are played).

Training your ears to hear compression such as this is a bit different from the framework because you are listening for different qualities in each compressor you train with (and yes, you will need to get very familiar with a wide range of compressors here). It can help to A/B test two compressors side by side and immediately notice the differences each compressor is adding.

In the above example, both compressors are introducing a whopping 20 decibels of gain reduction but are coloring the signal in noticeably different ways. The CLA-76 is softer and more fluid in comparison to the CLA-2A’s buzzing bright character.

While doing this, it is essential to keep a few questions at the forefront of your mind; how would you describe the coloration being introduced? What frequency band is being colored by this compressor? What circumstances would call for this style of coloration, and what would a different compressor do differently in this same circumstance?

The more time you spend thinking about which compressor works under which circumstances, the quicker you will instinctively reach for the right tool at the right time.

Listening For Depth

Adjusting the attack and release parameters of a compressor can help shape transients and ADSR envelopes of a sound and is a natural evolution of controlling dynamics overall. Setting a medium attack on a compressor can be an overly obvious way to bring out the thump of a kick drum or the pluck of a guitar, so let's talk about something else that envelopes can do to a sound (and a mix overall); they create the perception of depth.

I mentioned above how the human ear acts as a natural compressor, so consider how much more detailed nearby sounds appear than ones further away. For example, setting longer attacks on the compressor allows for more detailed transients by adding extra detail to the first few milliseconds of the sound, which creates perceived proximity of the sound within the mix.

Training your ears to recognize compression in this context isn't so much about identifying compression of the individual sound. Instead, it's more about recognizing how the rest of the mix is responding to the altering envelopes of the affected sound. Humans perceive depth by comparison, and removing the details in the transient of one sound (by using a faster attack) will make every other sound appear nearer by contrast. Conversely, if a compressor draws out the pluck of a guitar, then every other element will begin to be pushed to the background.

Hearing Depth in Action

As you've been training your ears to hear compression, you have likely been listening to the compressors and sounds in isolation to hear just what the compressor is doing. But now, we are going to be listening for context, which requires a few extra elements added into the mix.

Select a primary element whose envelope and depth you want to affect (I would recommend one of the same guitar or sax loops we were working with above), and add a couple of additional musical layers. Pianos, pads, soundscapes and drum loops all work great here, as long as all of the elements are playing at roughly the same volume. Below is a rough composition with many elements fighting for attention; the guitars fluctuate in volume, which fights with the arpeggiated sequence at odd times throughout the loop, resulting in a fatiguing listening experience.

Now go through our same compression framework, but instead of listening to the specific compressed sound, pay more attention to the rest of the mix. How do the additional layers respond to the signal being compressed? Do your pianos drift to the foreground as the compressor removes the transients?

Listen to the below example as compression from the API 2500 is applied and notice how it pushes the guitar further back in the mix, allowing the arpeggiated sequence to better grab attention. Note that the output gain has been matched, so the guitar’s volume remains the same throughout.

Try using a variety of compressors for this practice as well, as some compressors, like the Abbey Road RS124, tend to add more bite to the attack. Others have a smooth and almost musical release. All of this can play a massive role in how near or far a sound is perceived to be in a mix.

Final Thoughts

Training your ears to hear compression will take practice (there are courses out there, for example, by Hyperbits, that will help). But at least the process of improving is now demystified. Training your ears to hear compression all comes down to hearing many different instruments, in many different contexts, using many different compressors.

Want more tips on which compressors to use? Check out this in-depth blog on which compressor to choose for your mix.

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