Compression is a ubiquitous tool in the music production process, influencing the recording, mixing, and mastering stages. It can be surprisingly challenging to hear compression if you don't know what to listen for. At the same time, learning how to hear compression is critical as compression affects multiple vital aspects of a mix.

Fortunately, any musician can learn how to hear compression with a little bit of guided training. Below, we'll give you the complete rundown on how to hear compression and a brief overview on how compression works so that you can have full control over your mix.

What Exactly is Compression and How Does It Work?

In order to learn how to hear this common audio processing method, it's essential to understand the goals of compression. Audio compression allows engineers to control dynamic range, which is a fancy way of saying it helps you balance out the difference between the softest and loudest parts of a piece of audio.

Compressors are more or less focused around gain reduction, bringing down the highest levels of loud sounds while simultaneously amplifying the quiet parts of a track. This way, the processed audio becomes more consistently smooth throughout, producing a balanced, consistent sound.

A compressor comes into effect based on your chosen threshold. The threshold sets the point at which your compressor clamps down on a sound, for instance, once a threshold passes say 40 decibels, it gets to work.

Compressors have other controls like ratio (the strength of the compressor), attack (how fast the compress clamps), release (how fast the compressor releases the clamps), and makeup gain. Since a compressor is applying gain reduction to reduce the peaks of loud sound, sometimes gain is added to the final output to increase perceived loudness.

How to Hear Compression: 8 Strategies

Mastering compression's attack and release controls can only be done if you're able to hear how compression is affecting your mix. Here are some proven strategies to help you dial in the compression of your next track:

Use Your Bypass Tool

When in doubt, use the simple bypass tool on your plugin to listen to the audio with compression on and with compression off. Listen for a "pumping" sound whenever the compressor is on and compare that to the audio without applied compression. One of the easiest places to notice the processing difference is with drum sounds. Try putting a compressor on your drum kit and experimenting with release and attack time settings. With a little experimentation and critical listening, you'll start to understand how each compression toggle is affecting your mix.

Watch Your Meters

You can blatantly see the effect of compression in action by using a meter, like a VU meter. A VU meter, or standard volume indicator, showcases the average level of sound intensity over time. VU meters will become more consistent with compression since your perceived volume level will have less fluctuation.

Start Strong and Pull Back

One of the best ways to learn how to hear any effect or plugin in your mix is to start with fully extreme settings, and then pull back to a more reasonable level. For instance, you might start with a fairly harsh attack and set a low threshold so that you can hear exactly what your compressor is doing once it's put into motion.

Play with other settings like ratio, knee, and makeup gain one at a time to hear how each setting affects the overall sound. You can understand what all of these controls do to a sound logically, but hearing them in practice is another story. Another way to go about doing this is to place your compressor on a send and return track and play with how much of the signal you send through the return.

You can also experiment with the balance via a dry and wet knob if you're compressor has one of those toggles built in. The more wet the sound is, the more compressed it will be whereas fully dry will constitute a track that has no compression applied to it.

Focus on the Transient

Transients are the high peaks in an audio waveform that act as short bursts of energy at the beginning of any sound. Compressors can be used to effectively train these transients, particularly on the track sound of a drum kit, soloed snare drum, or any audio that has a loud initial peak and then mellows out after a snappy initial attack.

If you're having trouble hearing compression, listen to how the natural dynamics of the transients shift once you apply compression. You'll find that the peak is reduced and more consistent with the dynamic range of the rest of the song. Taming transients is particularly useful with percussive instruments, but it can be adept at smoothing over dynamic vocals or loud instrumental parts.

You'll hear the transient of a sound become compressed, while the quieter sound following the transient will be less affected by the compressor. This is because your threshold settings are more or less designed to target the outliers of your dynamic range to bring them to a more balanced, middle ground.

Listen for Depth and Coloration

Not all, but some compressors can be used to color or add character to sound in addition to controlling the dynamics of audio. Some common types of coloring compressors include FET-style compressors or Field Effect Transistors, or generally any VST compressor modeled after an analog piece of equipment. Some common options for coloring compressors include LA3A, Fairchild 670, or Waves Audio SSL G Channel.

If you're interested in trying out a free coloring compressor, you can download the TDR Molotok for free here. Listen to how a coloring compressor adds warmth and potential saturation to a track without sounding unnatural. Compressors are often used during the recording, mixing, and mastering process for this reason alone.

It's not uncommon to use multiple compressors within a single audio effect chain. One of your compressors might be used to tame dynamic, while another might be targeted towards adding warmth and color to your audio.

Hone in on Dynamic Differences

A surefire way to hear compression is to duplicate your affected track, one with your compressor enacted and another with the compressor set to off. Solo out each track and listen to the dynamic differences. If you wanted to get a clear visual, you could even print the compressor effect onto the track and compare waveforms between the processed and raw audio. You'll probably notice that the processed waveform has more of a consistent look, with less stark peak levels than the original audio.

Listen For the Compression Tails

One way to hear compression in your mix is to switch between the fastest and slowest attack settings and note the difference between the different configurations. You can also do this with release controls, listening to how the tail of the sound is affected as the sound wave passes through the compressor. Hearing how the compressor clamps and releases will give you a good sense of how the compressor is affecting the dynamic range of the audio.

Fast attack and release settings will create more of a punchy sound, while extremely short release times will build a more consistent, gradual progression of sound.

Iron Out the Sibilance

Controlling sibilance, or the harsh consonant sounds like "S"s, "P"s, and "T"s in a mix, is one of the most common scenarios in which engineers employ a specialized type of compressor known as a de-esser. De-essers are compressors that are dialed into a specific frequency range, made to target these harsh consonants or sibilance.

Take a vocal track and throw on a de-esser. A lower threshold will lead to more compression, with a higher threshold making the effect more subtle. Pay attention to how adjusting this control changes the auditory perception of sibilance over the course of your mix.

It's worth noting that you can also use specialized compressors to target other specific frequency ranges. You can use a dynamic compressor to control dynamic or transients centered around a set frequency band so that you're only compressing the needed frequencies, without losing some of the dynamics of a mix where compression shaping is otherwise unnecessary.

Understanding the Different Types of Compressors

Keep in mind that there are many different types of compressors. While all compressors control dynamics in some way or another, the exported sound profile will differ from one type to another. In addition, some compressor types are better suited for certain sonic situations over others. Here are some of the most common compressor types you'll come across:

• FET Compressor: FET compressors have a colored, stylistic sound that emulates a classic tube sound. They are known for adding punch, color, and warmth to a mix.  
• Glue Compressor: Glue compressors, as you might have guessed, are built for gluing tracks together. This is perfect for processing multiple takes of background vocals or bringing together related instrumental parts.
• Multiband Compressor: As the name suggests, this compressor has multiple flexible frequency bands you can use to adjust the intensity of the compressor across the audio spectrum.
• VCA Compressor: These compressors are known for having a fast response making them a great choice for taming unruly transients on sounds like drums. These compressors are known for being fairly clean sonically, making them very versatile tools when it comes to processing audio.
• Dynamic Compressor: Dynamic compressors can be used to toggle compression during a specific section of a song, in response to another piece of audio, or isolated to a particular frequency range.
• Sidechain Compression: This isn't necessarily a standalone type of compression, but you can use sidechain compression to process audio in response to something else. For instance, it's common to use sidechain compression on the bass in response to the kick drum. This way, whenever the kick drum hits, the bass is compressed to make room and lessen the overlap between competing frequencies.
• De-Esser: This is a specialized type of compressor that's set to affect higher frequency ranges, targeting the interference caused by sibilance from harsh consonants.
• Limiter: You can think of limiters as supercharged compressors or compressors with a 10x or more ratio. Limiters are used fairly sparingly, often in the mastering process as the final processing piece before exporting a finished piece of audio.

When in doubt, take the time to test out several different compressors on the same sound and compare and contrast. It's always good practice to get to know your gear so that you can cater your sonic decisions appropriately. You can also look up most compressor plugins on YouTube and listen to live demonstrations there before you opt to buy one compressor over another.

How to Use Compression in Mixing and Mastering

There are plenty of ways to use compression throughout the recording process. While some engineers prefer to use compression exclusively after the tracking phase, some may opt to insert a hardware compressor in between a preamp and audio interface. This way, you can create a clean, balanced, and sometimes colored sound coming into your DAW: the tradeoff is that you can't take out compression that's baked into your raw recording.

Otherwise, compression is primarily used during the mixing stage for any number of tasks. It could be used to add saturation and color. It could be used to bring together individual parts within a larger context, like vocal tracks within a vocal group. In any case, a compressor's job is to create more of a balanced listening experience.

During the mastering stage, compression is often used globally on the master bus to tame dynamic range or add color to the full mix of a track. While compression is a universal and vital tool for any audio engineer, it's important to note that you can go overboard with compression.

Overly compressed audio can sound unnatural and lose some of the dynamic intensity which makes a track sound human and full of life. It's particularly important not to over-compress vocals, as you can quickly lose some of the valuable energy of lyrics and expression with too much of a good thing. With the help of these strategies, you can start to hear and sense where compression helps and hurts throughout the music production process.

Once you can hear the effect of compression, you'll slowly become an expert in controlling dynamics in your music. This skill alone can take your tracks from sounding amateur to holding a professional balance. Enjoy using these strategies to hone in your recording, mixing, and mastering skillset.