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

Audio dynamics describes changes in the level of a recording or musical passage. Its dynamic range is the difference between its quietest and loudest parts. A wide range has a large level difference; a narrow range has a small one.

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?

Compare Audio Dynamics Online

Choose a processor in this online tool, then compare the sound before and after treatment.

Spoken example transcript: “Six small steps can shape a clear, steady message. Listen for the soft s sounds, then leave some space.”

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 reduces dynamic range by turning down signals that exceed its threshold. Makeup gain can then raise the overall output, making quieter details more audible relative to the peaks.

Compare the untreated loop with compression, then listen to the difference between its quieter and louder hits.

How does a Compressor work?

A Compressor responds to a predefined threshold, measured in dB. In downward compression, levels above that threshold are reduced according to the ratio, attack and release settings. Quieter passages are not raised by the threshold itself; that requires makeup gain or a different type of compressor.

For example, a drum loop may have occasional cymbal peaks that stand out. Set the threshold below those peaks and adjust the ratio and attack to control them. The useful threshold depends on the level of the recording; there is no single correct dB setting.

With an uneven vocal, compression can reduce the difference between loud and quiet words. Makeup gain may then bring the quieter words forward. It cannot recover words that were masked, clipped or not captured clearly; editing and volume automation may still be needed.

Vocal recordings often vary considerably in level, so compression is widely used to help them sit in a mix. Poor intelligibility can also come from background noise, microphone placement or the mix, so compression alone is not always the solution.

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: Describes how much an input level above the threshold is reduced. At 4:1, an input increase of 4 dB above the threshold produces an output increase of 1 dB above it.

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: Controls how gradually compression is introduced around the threshold. A hard knee changes the ratio abruptly at the threshold; a soft knee introduces it across a range of levels. Attack controls the response time.

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.

Compare the original peaks with the limited signal.

A Limiter uses strong gain reduction to control peaks. Its output ceiling sets the maximum permitted output level; its threshold or input gain determines how much limiting occurs. A brick-wall limiter is designed to stop peaks crossing the ceiling, but not every high-ratio compressor guarantees that behavior.

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.

Limiting can help prevent a digital output from exceeding its ceiling and clipping. Heavy limiting can still reduce punch and introduce distortion. A sample-peak ceiling also differs from a true-peak ceiling, which accounts for peaks reconstructed between samples.

A limiter can be fairly transparent when it only catches occasional peaks. Its ceiling alone does not determine the amount of processing: driving more signal into it causes more gain reduction, even when the ceiling stays unchanged.

Limiters are often used in mastering to increase average loudness while controlling peaks. How much this changes the sound depends on the source, settings and amount of gain reduction; excessive limiting can flatten dynamics.

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: Delays the audio briefly so the limiter can detect a peak before it reaches the output. This helps it reduce gain in time to respect the ceiling, at the cost of latency. It does not mean allowing more peaks through.

Release: Sets how quickly gain returns after a peak. A short release may cause distortion or pumping; a long release may keep later sounds turned down. Choose it by listening to the material.

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.

Listen to the hiss between the drum hits with the gate off and on.

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 increases dynamic range. A downward expander turns down signals below its threshold; an upward expander raises signals above it. Both increase the level difference between quieter and louder material.

Compare the quieter tails and background hiss with downward expansion off and on.

A downward expander is useful for reducing low-level noise between wanted sounds. A gate is a more extreme version of this approach. Upward expansion instead boosts louder material above the threshold.

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 can reduce low-level noise or increase the contrast between quiet and loud material. It cannot exactly undo compression or reconstruct dynamics that have been lost.

For this reason, mastering engineers may use expansion selectively when a mix needs more contrast. The result depends on the source, and too much expansion can make levels uneven.

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.

Compare the same spoken phrase with de-essing off and on. Listen to the s sounds.

Spoken example transcript: “Six small steps can shape a clear, steady message. Listen for the soft s sounds, then leave some space.”

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.