Audio Dynamics (Compressors, Limiters, Gates, Expanders, De-Essers)

Audio dynamics is the concept that describes variations in the volume of music compositions and audio tracks. If an audio passage goes from quiet to loud very often, it is said to have a high dynamic range. If the opposite happens, it is said to have a low dynamic range.

In music, dynamics have been around since the dawn of time. They’re used as a creative tool, meant to add expressiveness to a certain passage. When a musician plays a loud note, he or she is purposely trying to add impact to a composition. 

Making good use of the dynamic range (going from quiet to loud and vice-versa) is a must in classical music, but all genres incorporate some sort of dynamic feel. That’s why terms such as pianissimo (playing very softly) and fortissimo (playing very loudly) exist in music theory.

Dynamics are essential for creating music and all musicians play with it, even if they do so intuitively. But why are audio dynamics so important to audio producers?

What are audio dynamics used for in music production?

In music production, audio dynamics are used to ensure that passages of audio have an appropriate dynamic range. Audio snippets that are too dynamic can have an excessive amount of volume fluctuation, hence being hard to listen to in a pair of speakers or set of headphones.

While dynamics have mattered in music since the first time a person picked up two rocks and played a rhythm, audio dynamics as a music-production concept are about recording and editing audio passages so they can be appropriately played.

Audio dynamics are essential not only for music producers but for all audio engineers. If the sound is being streamed, broadcasted, or even televised, audio dynamics is what makes it listenable.

Imagine you’re streaming a song that has poor dynamic control, with a chorus that is ostentatiously louder than the verses. This will make it uncomfortable for you as a music listener because you will be forced to adapt the volume of your speakers or headphones to each section of the track.

To avoid issues like these, audio engineers are tasked with ensuring that all commercially released audio has a comfortable dynamic range, not going from very quiet to very loud too often.

What tools can be used to control audio dynamics?

In music production, audio dynamics are controlled by a set of tools designed to reduce or increase the fluctuation in the volume of an audio passage. These include audio effects such as Compressors, Limiters, Gates, Expanders, and De-Essers.

While it’s possible to complete a song, a podcast, and even a film soundtrack without knowing what audio dynamics are, one thing’s for sure: if you don’t pay attention to the fluctuation in the volume of any audio snippet, it will most likely sound amateurish and make for an uncomfortable listening experience.

For this reason, understanding audio dynamics and the modern-day tools used to shape them is essential for any aspiring audio professional.

What is a Compressor?

A Compressor is an audio effect used to reduce the dynamic range in audio, by making quieter passages sound louder and louder passages sound quieter. To put it simply, a Compressor allows music producers and audio engineers to quickly reduce the volume fluctuations of a song or audio track.

How does a Compressor work?

A Compressor works around a predefined threshold level. The threshold level dictates the point (measured in dB) around which a Compressor will act.

Compressors work both ways when it comes to audio dynamics, helping producers not only to “squash” very loud peaks but also to “bring up” quiet moments in an audio passage. This depends on the threshold settings and on what you want to use the Compressor for.

Let’s explore two different scenarios. In the first one, you have a very cohesive drum loop recording that sometimes gets a bit too loud (maybe it has a high-volume crash cymbal, for instance).

To solve this issue, all you need to do is set the Compressor’s level at -2dB to 0dB, so it can control the crash-cymbal peak and make it quieter.

Next, let’s imagine you’re dealing with a vocal recording in which the singer wasn’t able to maintain a cohesive volume. Let’s even say that some of his or her words are so mumbled you can’t understand them.

In this case, you should set the Compressor threshold to a very low level (let’s say between -20dB and -10dB) to make the indistinguishable sounds made by the singer come up and become recognizable.

Vocal recordings (from singing to speech) are very unstable when it comes to volume, and are for this reason almost always processed by a Compressor. When you’re listening to a radio interview and you can’t understand what’s being said, it’s most likely because the audio broadcast is either poorly compressed or not compressed at all.

What are the main features of a Compressor?

In addition to the threshold—that sets the input level at which the Compressor will begin—these are some of the fundamental Compressor features you should know about:

Attack and Release: Sets how long it takes for the Compressor to begin to act and stop acting—respectively—according to a certain threshold. Compressors with an extremely short attack can give way to unwanted clicks and noises, while Compressors with a very long release can make a track feel muffled by excessively flattening its dynamic range.

Ratio: Sets the amount of attenuation applied to the signal. In mathematical terms, it’s the number of output-signal dB applied to each 1dB of the input signal. In simpler terms, it refers to how much of an impact the Compressor will have on the signal dynamics.

Makeup gain: A feature of some Compressors that automatically “makes up” for reductions in volume. This means that if the overall volume of an audio passage is reduced by the Compressor, the makeup gain will automatically make it as loud as before while keeping the changes in dynamics. It’s great for understanding how Compressors affect the expressive dynamic range of audio, not its perceived volume.

Knee: Used to adjust the Compressor response to the signal (i.e., input level) according to the threshold. A hard knee is fast and ideal to control high-peak transients (such as drums), while a soft knee is slower and best-suited for dealing with smoother instruments such as pads, acoustic guitars, pianos, etc.

What is a Limiter?

A Limiter is an audio effect that’s very similar to a Compressor, except it uses a very high compression ratio. In music production, a Limiter is generally used to increase the level of a signal without causing its peaks (i.e., its loudest points in time) to go over a predefined threshold.

The Limiter’s threshold is also known as the ceiling and defines the maximum level (in dB) that the Limiter will allow the signal to output. This is why Limiters are often described as brick-wall Compressors: since their ratio is set very high, they will stop any frequencies from going over a predefined threshold.

What are Limiters used for?

While Compressors are used to gently adjust the dynamic range of an audio passage, Limiters are much more assertive in the way they influence audio dynamics. For this reason, Limiters are often deemed to be a mastering effect and tend to be applied to the master channel.

The main purpose of limiting is to prevent a full track from clipping (i.e., going over the maximum allowed level of 0dB), ensuring none of its peaks gives way to unwanted distortion and sound artifacts. While this affects the audio dynamics, Limiters don’t have the same flattening effect associated with Compressors.

If used properly, a Limiter should be very transparent. The Limiter’s threshold is normally set very high (anywhere between -0.5dB and 0dB), which means that the Limiter will only act whenever the track it is processing goes over this value.

If applied to a track with decent headroom and few violent peaks, a Limiter will be effectively bypassed (i.e., turned off), at least for the most part.

Limiting is essential to mastering audio because it’s the best tool for increasing the loudness of an audio passage without also increasing its peak level. A Compressor can be used for the same effect, but will normally have a more significant impact on the overall dynamic feel of the audio, causing its sound to change more dramatically.

What are the main features of a Limiter?

The threshold/ceiling—which controls the maximum output level allowed—is by far the most important feature of a Limiter, but there are others:

Lookahead: Determines how quickly the Limiter will respond to loud peaks. A very short lookahead will be very effective in dealing with clipping, but can potentially make a track sound lifeless. A long lookahead may allow some tiny peaks to come through, but it’s good for preserving transients—which is ideal for “punchy” songs.

Release: Sets the amount of time it will take for a Limiter to stop acting once the signal drops below the threshold. The shorter the release, the more transparent the Limiter will sound. However, please make sure the release time isn’t too short to avoid clipping.

Gain: Makes the input level sound louder. The key to understanding how gain works in a Limiter is to keep in mind it is always added before the signal’s processed by the Limiter. This means that any gain boosting or attenuation will be limited by the threshold. This is why you can add lots of gain to a sound passage without causing it to clip, which is effectively what Limiters were made for.

What is a Gate?

In music production, a Gate is an audio effect that only allows an audio signal to come through once it goes over a predefined threshold. If you set the threshold of a Gate to -5dB, for example, all the instances of an audio passage that are playing under -5dB will be extremely quiet or muted.

To understand what a Gate does, you just have to think of its name. Like a real-life gate, a Gate is used to only allow the sounds that are over a certain threshold to pass through. Once the Gate is open, the audio passage it is processing will be audible. Once the Gate is closed, it will either be very quiet or not play at all.

What is a Gate used for in music production?

Gates have many functions in music production, from generating creative effects to shaping the sustain of short snippets of sound. However, they are mainly used to quickly clean up recorded tracks by getting automatically rid of very quiet audio that shouldn’t be there.

In general, Gates are required whenever there are drum and vocal recordings’ involved. In the first case, a Gate can help to separate drum transients from one another, making the snare-drum more distinguishable from the kick-drum (for instance).

This way, audio engineers can more easily edit drum tracks by getting rid of the unwanted sounds that are being played in between the transients.

In vocal tracks, Gates are used for achieving a similar goal. Since vocals are most commonly recorded by humans, they’re naturally filled with unwanted sounds, from little noises and clicks that happen during silent moments to annoying sounds generated by a singer’s breath and saliva.

Gate is a very useful audio effect for automatically cleaning up recorded audio passages, ensuring they will only play during the moments they’re supposed to play.

To use a Gate to good effect, you need to find the appropriate threshold. Imagine you’re trying to edit a drum loop in which the quietest noticeable sound is peaking at -10dB. In this case, you should set the threshold to around -10dB, ensuring the Gate only “opens” when a noticeable sound’s played.

In this case, all the little unwanted sounds that are being reproduced at less than -10dB will be attenuated because the Gate will be “closed.”

What are the main features of a Gate?

The threshold of a Gate is essential because it determines the level of dB a sound signal must reach for the Gate to be open. But there are other important features to keep in mind when working with Gates:

Floor: Sets the attenuation applied to the signal once the Gate’s closed. At -inf dB, no sound whatsoever will be reproduced. At -40dB, the “closing” of the Gate will not mute the processed audio track but will attenuate it considerably. At 0dB, there will be no attenuation—which would be the same as turning off the Gate.

Return: Sets the difference (in dB) between the signal that opens the Gate (the threshold) and the moment it closes. While often ignored, return settings are essential for a good-sounding Gate. If your threshold is set at -12dB and your return is set at 3dB, this means that the Gate will begin to attenuate the signal (according to the floor level) once it goes under -15dB.

Attack and Release: Sets how quickly the Gate will act and stop acting (respectively) according to the threshold. If you’re using the proper threshold, floor, and return settings in your Gate, you shouldn’t be too concerned about these. However, attack and release can help to make a Gate sound smoother and more natural.

Flip: A special feature you don’t find in all Gates, but that can be very useful. In a nutshell, it causes the threshold to act in the opposite direction, meaning that the Gate will open only when the sound signal goes under the predefined threshold level. It can be used creatively to make use of tiny noises and crackles in a recording.

What is an Expander?

In music production, an Expander is an audio effect meant to increase the dynamic range of an audio passage. It can be seen as the opposite of a Compressor, since it’s used to make loud peaks sound even louder, increasing the level of volume fluctuation in a signal.

This means that every time an audio snippet goes over the predefined threshold value, the Expander will make the sound louder instead of quieter.

While Compressors are used to flatten audio tracks that contain an excessive amount of volume fluctuation, Expanders do the opposite. 

Expanders are often included in Compressors as an additional feature, and their controls (including threshold, knee, attack/release, or ratio) work similarly to the controls of a Compressor, albeit the other way around.

What is an Expander used for?

An Expander is mostly used as an audio-repair tool. Sometimes, musicians will compress sounds so harshly that they end up losing all their dynamic range. That’s when Expanders come in handy since they can reverse this effect and restore some of the lost dynamics of an audio passage.

For this reason, Expanders make for a must-have tool for mastering engineers, who are frequently forced to work with poorly mixed tracks that feature an excessive amount of compression.

An Expander can give life back to an audio passage that was extremely “squashed” by a Compressor. An overly-compressed track can sound unnatural and lifeless.

What is a De-Esser?

A De-Esser is an audio effect specifically designed to get rid of high-pitched sibilant sounds unwillingly produced by singers. A De-Esser manages to do so by acting as a Compressor that only attenuates the volume of a predefined set of very high frequencies, usually between 7 kHz and 17 to 19 kHz.

What is a De-Esser used for?

A De-Esser is used to clean up vocal recordings by attenuating the “S” sounds produced by singers. Not all syllables are made the same, and s-sounding words can be very harsh on the ear. A De-Esser manages to attenuate these specific syllables by acting as a super-high-frequency Compressor.

Imagine you’re working with a singer who recorded a glorious take but was unable to contain his or her excitement when singing the word ‘success.’ Luckily, these ear-cutting, annoying “S” sounds can be tamed with the help of a De-Esser.

De-Essers tend to include some presets that are excellent at tracking these frequencies and lowering their volume, hence making for cleaner vocal recordings and less sharp “S’s.”

While De-Essers are seldom used for different purposes, they can also be effective to clean up harsh-sounding cymbal recordings and smooth some soft-synth patches that may contain an excessive amount of high end.

What are the main features of a De-Esser?

Like most audio-dynamics effects, De-Essers are also controlled by a threshold. The threshold sets the level above which the De-Esser will attenuate the sound. When it comes to De-Essers, the threshold’s set at a very low level (usually -30dB and below).

These are the other key features to keep track of when working with a De-Esser:

Frequency range/filter slider: Known by many names, this feature determines the frequency range impacted by the De-Esser’s attenuation. If it’s set between 7 kHz and 17 kHz, for instance, the De-Esser will only impact the frequencies between these two values. When setting the frequency range of a De-Esser, keep in mind it can impact the brightness of a track without causing significant “S” reduction if too high (I would advise against setting it above 19 kHz).

Range: Determines the scale of dB reduction applied by the De-Esser. This control is mainly used to prevent the effect from taking too much volume away from the recording.

Lookahead: Sets the amount of time the De-Esser will have to anticipate sibilant sounds and attenuate them. If you feel like your De-Esser isn’t properly capturing all the “S’s” in a vocal recording, setting a higher lookahead time is a good way to make sure it deals with unwanted “S” syllables more effectively.

Summary

Dynamics, when it comes to music production, is what allows listeners to be able to make sense of different volumes.

Imagine you’re streaming a song that has poor dynamic control, with a chorus that is ostentatiously louder than the verses. This will make it uncomfortable for anyone listening on speakers or headphones to have to adapt the volume of their speakers or headphones to each section.

To avoid issues like these, audio engineers are tasked with ensuring that all commercially released audio has a comfortable dynamic range, not going from very quiet to very loud too often. Compressors, Limiters, Gates, Expanders are just some of the tools used for dynamics by audio engineers to make their tracks sound more professional.

Understanding the concept of audio dynamics is important for any aspiring audio professional because it will give them a leg up on their competition and make their work sound more professional and richer with every use.

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