When you’re mixing, you want to have control of the dynamic range of your audio signal, so you typically load a compressor and start tweaking the controls. Attack and release times are paramount not only for the compression process but also to enhance the overall performance and perceived loudness. In this article, we’ll take our 7 years of industry experience to explain how attack and release work and how to dial in the perfect attack and release settings for any instrument!
What Is Attack & Release In Compression? (TL;DR)
These two settings control the reaction time of the compressor when the input level hits the threshold. The attack time is how long before the compressor kicks in, and the release time is how long before the signal goes back to its original position.
Different combinations of these settings can bring you to drastically different results, like controlling dynamics of sloppy performances, level uneven dynamics of a full mix in a mastering situation, or just taming unruly peaks.
Using a fast attack time is good to tame spiky transients and combined with a fast release time it’s great to increase the perceived loudness, but can cause unwanted ducking if the compressor isn’t too fast.
Using slower attack times along with slower release times can help round up dynamic performances, so they’re great to level up vocals or round up a bass performance. On the downside, these settings will murder your drums because the slower release time will take too much of the transients.
How Do Attack and Release Affect Compression?
These settings control the time and duration of gain reduction. When the input source reaches the threshold level, it makes your compressor react in a period of time, this period is set by the attack and release.
To know how a compressor’s attack and release settings can affect your audio, it’s important to understand the different parts of a waveform: attack, decay, sustain and release, A.K.A. ADSR envelope, and how this relates to the actual controls in the compressor.
- Attack – The attack is the time it takes to go from silence to the loudest part of the signal, it’s also known as transient. Sounds with fast attack times tend to be more percussive and snappy, whereas sounds with slow attack speeds sound like they fade in, like synths and pads.
- Decay – This is the time it takes a sound to go from its peak to the sustained volume. This is more noticeable in a bass guitar or a synth with a loud attack and low sustain volume (IMG)
- Sustain – It’s basically the resting point of a sound, for example, if you hold a note on a guitar, the pick scrape is the attack and the note is the sustain.
- Release – This is the time it takes a sound to go back to the silence after the sustain. In synthesis, it’s the time it takes for the note to fade out.
Now, the compressor attack setting will determine how much of the initial transient (or attack) it’s going to be attenuated by gain reduction, which means that you can either emphasize or flatten this part of the waveform depending on how long your attack is set, your release settings, and your ratio settings.
For instance, if you use a fast or short attack, it’ll cut down the transient, which can be good for overly dynamic input signals that need to be controlled but can also cause unwanted distortion, overcompression, aliasing, and pumping. It’s also a very bad thing to do to your drums, more often than not.
On the other hand, the release control in the compressor pretty much mimics the end of the waveform, so it settles the time to go from maximum gain reduction to none, similar to the “fade out” at the end of a waveform.
Using short-release speeds is great for treating percussive elements or limiting when mastering certain genres like metal or EDM because the compression affects the sustain of the waveform but preserves the attack and decay. Slower release times are often better for glue and macro dynamic control.
So, in practice, imagine you’re compressing some MIDI drums on a rap beat.
You can see that it isn’t particularly dynamic, but it sounds very thin and its transients need control because they’re all over the place.
We set up a ratio of 4:1, set our threshold, and now we need to determine the attack and release times.
If we use fast attack and slow release, we’re going against the signal because it’s mostly transient information and very short decay, sustain and release.
As a result, we are, of course, bringing a lot of details forward, but we’re pretty much killing the entire song.
You can see how the dynamics are dead and the drums sound dull and lifeless and boring.
On the other hand, using slow attack and fast release settings keeps your transient information as it is.
It also helps the drums sound fuller and even though we’re applying more than 7dB of gain reduction, the drums are still pretty dynamic.
Drums also sound bigger with these settings.
How Do I Set The Perfect Attack and Release Settings?
When I’m looking to set the perfect settings for any signal, the first thing I take into consideration is the performance, type of source, then genre, and finally what sound I’m looking for in the signal. If I’m not convinced with the results, or am uncertain of what the best times can be, I use a couple of formulas to quickly get in the right direction.
Whatever the case, these are a few quick and easy tips that work.
Regardless if you’re compressing drums, bass guitar, or mix bus, it’s important to be mindful of the performance in terms of how much space is there from one note to the other, the type of sound and its role in the mix because these settings have a huge impact on the overall emotion and excitement of the sound.
For instance, if we have this bluesy guitar peak, the first thing to notice is the accentuations of the performer to the open notes. He’s clearly trying to be smooth.
Then notice that there are a couple of fluctuations that we might want to fix, but we can’t touch its natural dynamics because of its rhythmic nature.
For this reason, we’ll use a fairly slow attack and a relatively short release and compress no more than 2-3dBs to preserve the dynamic range.
Right off the bat, we can notice how compression increased its perceived loudness and made it more open.
The guitar sounds more controlled, and less spikey during the palm mute. Additionally, the compression rounded it up and made the whole tone richer, fuller, and smoother.
Type of source
For example, you’d use a mild to slow attack and a relatively slow release time for a vocal performance to make it sound bigger, but if you try these same settings on a kick drum, it’d sound dull and lifeless.
Also, the frequency domain is important to consider because different frequencies require different response time settings. For instance, to compress bass frequencies is better to use slow attack times and high frequencies with fast attack speeds.
The reason why is that the higher frequencies tend to travel very fast, which means that if you use a slow attack your compressor might not even be able to catch them and if you combine them with a slow release you almost automatically overcompress and make it harsher.
This is pretty important but often overlooked. The genre often dictates how things are going to be processed. For instance, you’d not compress a soulful vocal in an R&B mix the same way you would do a rock vocal.
So, in this case, suppose we’re mastering and going to compress these songs:
Sample A needs better glue because it sounds all over the place and needs to feel more cohesive and move. EDM needs to be danceable, so we will use the compression in a way that exaggerates dynamics to create movement because the mix sounds a little flat.
Here we’re looking to bring things forward, we’re looking to increase the decay and sustain, which we’ll do with a mild attack time of 1s and a quick release of 50ms.
The ratio was set at 1.5:1 and we’re using a hard knee so the compressor only engages when needed.
Sample B has excessively tall peaks, which decreases its perceived loudness and will be a pain in the limiting stage. We need to keep it very organic and very delicate because jazz, blues, and similar genres are very much about the feeling of the performance, so you can’t go too crazy with compression because you need to preserve dynamics.
In this case, we’re compressing with a 4:1 ratio, which is far more aggressive than our prior example.
We’re using a very fast attack of 0.5ms and a rather quick release of 0.3s. Like before, the knee is set to a hard knee, so that it only engages when the drums hit to chop down the transient.
Lastly, our sample C is an R&B/Hip-Hop, and similarly to the EDM mix, we want to increase the movement but we also want it to be vibey. Hip-Hop is all about the flow, for a lack of a better word, so we need to preserve dynamics, but also bring forward the details of the beat and the vocals.
Here we need to tighten up the kick and snare and glue the mix together, as it feels pretty loose and things feel separated from each other.
We’ve set our compressor ratio setting to 3:1, a slow attack time of 3s, and a relatively fast release of 0.3s.
Sometimes you’d use compression not to control or shape the dynamic range of your track, but to create a specific effect. Maybe you want to make something more distorted or create a pumping effect to help the groove.
Attack and release can help you a great deal with this type of thing too, for example, if you want to distort something and make it louder in the process, you’d combine the fast attack and release with a high ratio setting and a hard knee.
If I’m creating a pump effect usually a fast attack and slow release with a sidechain-triggered compressor work really well, even more, if you use a low threshold setting and pretty aggressive ratio, although this would depend more on how your tracks sound and what you need to achieve.
Yep, we’re engineers, sometimes we use math, and it’s incredibly effective and adaptable, which accelerates your workflow a lot. I often use these two formulas to time my compressor attack and release:
Converting BPM to milliseconds
This one’s pretty straightforward and can help you accentuate the beat and rhythm of your mix making it more exciting for listeners. Basically, you only need to divide 60,000/BPM and it’ll give you the value of a quarter note in milliseconds.
Depending on how fast or slow you need your attack and release times to be, you need to know that the resulting time is the length of a quarter note, so you can divide the result by 8, 16, 32, and 64, or multiply times 2 or 4, to stay in tempo.
Converting frequencies to milliseconds
This is a great way to compress individual tracks and ensure a nice transparent compression It’s also very good to use in mastering situations when you’re regulating dynamics.
To use this formula effectively, we’re going to need a frequency analyzer and find the lowest harmonic. That frequency is the value we’ll use to calculate the perfect attack and release time.
Compressor Attack and Release Tips
When using dynamic expansion
One interesting thing to do is dynamic upward expansion to improve the shape of the spectrum more musically. Keeping up with the previous example, imagine that we’re shaping the tonality of our mix bus, so after the compression settings are dialed we add a multiband expander, in this case, FabFilter’s Pro MB.
We add our crossover bands and make sure to change the slope to 12dB/oct to have a more musical effect and prevent phase shifting, and then we need to set our compressor attack and release times for each frequency.
In this case, Fab Filter’s plugin uses a percentage, so I don’t really know how long the attack and release actually are.
We’re using a 27.4% attack and 79% release on the low band, 43.6% attack and 55.7% release on the low-mids, 25.5% attack and 43.8% release on the mid-range, and 20% attack and release on the top end.
To shape the spectrum, we used downward compression, except for the mid-range, for which we used upward expansion to add clarity and openness
You need to know that in ProMB, 0% is extremely fast and 100% extremely slow, so it’s as simple as spinning the knobs until you land in the right settings.
In this case, we have this drum loop and bass which are lacking low-end, and will fix it with the Weiss DS1-MK3 compressor.
Since I need to know how long to set the compressor and need to be very precise to only affect the frequencies of the bass without getting the kick drum going all over the place, I’ll look on an analyzer for the lowest frequency and use the formula to convert it to milliseconds.
Low frequencies work better with a slow attack, but in this case, we’ll go with 50ms to prevent the kick drum from getting too loud. This compressor lets me use two release times parallelly, so I’ll set the slow release to 200 and the fast release to 100ms balanced towards the slow one so that we can let go of the kick drum quicker with the fast release but keep the sustain of the lower notes at the bottom.
Simply watch how the low frequencies sound rounder and tighter. This process is particularly important for bass-driven genres because low frequencies tend to cancel each other out, so properly compressing the low end can help these elements to coexist together and ultimately be reproduced in any audio player.
Lastly, you can combine different settings to make something sound farther or closer in the stereo field. For example:
- Fast attack times and fast release make things sound closer because the compressor chops off the initial transient but doesn’t stay long enough to affect the sustain.
- Fast attack times and slow release make things sound farther because the compressor flattens the full waveform, so we perceive that the signal drops in volume.
- Slow/medium attack and fast release times usually lead to a transparent and more musical compression.
- Slow/medium attack and slow release times are good to enhance the sustain of an audio signal or sweeten up a performance.
A Brief Overview of Compression Settings
Here’s a quick overview of all the compressor settings:
- Attack & Release – attack time is how fast the compression occurs, dictated in milliseconds or seconds, and release time is how long it takes to relinquish the compression.
- Makeup Gain – after the compressor does its thing you can then increase the overall volume using the makeup gain
- Ratio – how much gain reduction is applied once the signal passes the threshold.
- Threshold – the volume the signal must pass before the compressor kicks in.
- Dry/Wet – also known as ‘Mix’, this option lets you blend the dry and wet signal (with compression and without compression) in order to achieve a more natural sounding output.
Javier is a mixing and mastering engineer who specializes in Rock and Hip Hop, and writes and produces his own music. He is additionally a TV, Film, and advertising audio editor who has been working freelance for 7 years. He loves sound design and is an avid expert in his field, having written hundreds of articles for other publications online about music production-related topics. To put it simply – Javier knows his stuff.