Audio compressor settings chart
The audio compressor is probably one of the hardest processors to understand and set up. Having an audio compressor settings chart will help if you are a beginner.
When I first started using a compressor, I couldn’t even hear what it was doing to the signal. I’d been used to using things like chorus and reverb! One of the reasons they aren’t straightforward to set is that in explanations, mathematical jargon usually gets quoted.
While an audio compressor settings chart is a good place to start you will get better results if you learn how to set an audio compressor yourself.
This is because almost all sounds, levels and recordings are unique. If you follow a settings chart for drums, the drum sounds you use may be nothing like the ones that were used to come up with those settings.
The good news is that even if you don’t understand how compressor settings alter the sound, the audio compressor settings chart will almost always make your recorded track sound better.
This article refers to both hardware devices and plug-ins. The terms and controls are the same. This is very much an introduction and you should refer to my other guides for tips for using compression on vocals and glue compressors for compressing the whole mix.
Tip
It can be difficult to remain objective when mixing. If I’m not sure about the compression I do a few different mixes and write down the settings. Something like mix A vocals 4.1, mix B vocals 2.1 and listen back the next day. You’ll hear things you won’t believe you missed!
Audio compressor settings chart or cheat sheet
These are the settings I usually start with.
| Track | Ratio | Attack | Release |
|---|---|---|---|
| Vocals | 2.1 – 4.1 | 1ms | .5s |
| Backing Vocals | 2.1 – 6.1 | 1ms | .5s |
| Electric Guitar | 4.1 – 8.1 | 2ms | .3s |
| Acoustic guitar | 2.1 – 4.1 | 5ms | .3s |
| Piano | 2.1 – 6.1 | 1ms | .3s |
| Bass | 4.1 – 10.1 | .1ms | .3s |
| Drums | 4.1 – 8.1 | 10ms | .1s |
| Whole Mix | 2.1 | .2ms | .5s |
Tip
Remember these are just general starting settings. Once you understand the compressor more, don’t be afraid to experiment and do what sounds best for your mixes and music.
What does a compressor do
Basically, it squashes the audio signal into a smaller signal by reducing the peaks.
When you record a signal, you set the fader so the signal doesn’t drive the system into the “red”. By squashing the peaks you can have the faders higher before the “red clipping” occurs so effectively you have a higher overall average level. You are reducing the range from the quietest sound to the largest sound.
Setting a compressor can be something of a balancing act. No compression will mean the signal levels of parts can vary too much. Some parts will be too loud and some will be too quiet to hear.
A compressor will make a mix sound much better if used correctly. It can also be overused and too much compression can lead to a dull lifeless undynamic and, for want of a better descriptive word “over-compressed” sound.
The compressor settings
Obviously, not all compressors will have exactly the same settings.
There would have to be a lot of different guides to cover all of the different compressors and plug-ins so what I’m going to do is just go through the standard most used and important ones. You can learn about the other more obscure ones later once you have a basic grasp of what you are doing and more importantly, why.
The threshold setting
You’ve got to start somewhere, so let’s get going with the threshold setting as it’s one of the easier controls to understand.
Start with the threshold control turned all the way up to its maximum setting. No compression will be taking place with this turned up because the threshold setting controls the level that which compression happens.
All of the levels of the signal will be below the threshold setting, hence no compression. As you lower the threshold, you will get to a point when the peaks of the signal are above the threshold and so will get compressed. The lower you set the threshold the more of the signal is above the level, so more of the signal will get compressed.
If you set the threshold so it’s about half of the level of the signal, the top half that exceeds the threshold gets compressed but not the ones below, which remain at the same level.
Ratio settings
The ratio controls how much compression takes place.
It’s common to see compression ratios start at 2.1 and go up to 10.1 as these are the most usable ranges, as you can see from the Audio compressor settings chart.
Sometimes the ratio control is switched like in some of the older hardware “real” compressors. In this case, the plug-ins usually have the same switched control, such as the SSL glue compressors. These had ratios of 2,4 and 10. You may find that your compressor has a fully variable range.
These can go from 1.1, which is no compression to an infinity setting. The infinity setting is quite interesting as it means that if set, the output won’t get any higher. It limits the output to the value of the threshold and you may sometimes see “limiters” mentioned as dynamic processors.
If your compressor has an infinite ratio you can use it as a limiter. A lower ratio will give you less compression. If you set the ratio to 2.1 it means that in practice, once the signal exceeds the threshold by 2dB the actual compressed output will be 1dB over the threshold.
If you set the ratio to 4.1, it will take a signal of 4dB to produce a 1dB output above the threshold.
Attack time
The attack time is the time the compressor takes to work or compress the signal.
It usually has markings in milliseconds and the quickest time is usually around .1ms. This is pretty quick! The attack time on the SSL bus compressor goes from .1mS to 30mS. At its minimum setting, the compressor will start compressing almost immediately but as you increase the time, any fast percussive attacks will go through uncompressed.
When you compress the audio range of a signal you are effectively squashing it so you can have it louder before it clips or drives the system into the red. You do this at the cost of reducing the range between the loudest and the softest sounds.
This can be an advantage when the range is too much. When the loud sounds are too loud and the quietest sound is inaudible. Compression makes sounds that are too loud quieter, and the quiet sounds, louder. This reduces the dynamic range and on some sounds, it can reduce the impact.
This can be evident on drum tracks, so by increasing the attack time, the impacts that the drums make get through unaffected. As I mentioned in the section, “What does a compressor do”, it’s a balancing act of trying to compress without overdoing it!
Decay time
In the way that the attack sets the time before the compressor starts to work or compress, the decay time sets the time that the compressor takes to go back to the uncompressed start.
If you set it too slow you will be compressing the signal when you don’t necessarily need it to. If you set it too fast you will hear the compressor effect. By that I mean you’ll hear it working”. That’s the changes in volume or pumping effect.
The attack and decay are controls that are best tweaked together to get the compression you want but without the side effects. That is if you don’t want to hear the side effects.
The pumping sound is sometimes used as a dynamic effect in itself. Especially in dance music. As it can be rhythmically used on certain parts. Sometimes there is a setting on decay that when it’s fully turned to the maximum it becomes auto. This attempts to set the correct decay of the signal.
Sometimes this works very well depending on the track and it’s worth giving it a go and a listen.
Makeup
This is probably the easiest control to understand.
It’s basically volume control for the device. If you apply a lot of compression to a signal it will appear to be a lot quieter. The makeup control “makes up” for the loss of volume. You can set the signal to be the same as it was before it was compressed.
Wet/dry control
This is one of the rarer compressor controls so don’t worry if yours doesn’t have it.
Without a wet/dry control, the output will just be 100% wet, meaning the whole of the signal is compressed which is usually what you want from dynamic processing. If you have a wet/dry control on a reverb unit, the “dry” sound is just the original signal and the “wet“ is the reverberation signal.
You set the wet/dry control to balance what you hear. It’s the same with the wet/dry control on a compressor. Normally you’d want it at 100% wet, so all of the signal gets processed.
If you’ve ever heard of the term “parallel compression”, this control enables you to achieve it without any other routing. Without a wet/dry control, you’d normally have to route the unprocessed signal through another channel and use this channel and the compressed one to achieve a wet/dry mix.
The audio meter
The audio meter of a compressor is a very useful addition.
If there isn’t a switch on it it will usually show you the amount of compression that is happening to your signal. You’ll see the compression shown on the meter when you lower the threshold or increase the ratio. If you’re putting something percussive like a drum track through it you see less compression occurring if you increase the attack time control.
This is because it’s letting the initial attack of the drums through uncompressed before the compressor kicks in. If the meter switches, it usually switches between signal input, compression amount and signal output.
Some compressors such as the compressor built into Ableton Live show the meter with a scrolling time, right to left. This is particularly useful as you can “see” what’s happening. It’s especially useful for setting attack and release times in addition to the signal and the compression happening.
Knee
Another setting you may come across is the knee setting.
When the ratio is set high and the signal exceeds the threshold, there will be a “bend” as the signal no longer increases linearly. This point can be a very definite point and this would be a hard knee. If this point becomes less defined or rounded it becomes a soft knee. You get the idea if you look at the pictures of this term.
A soft knee sounds more “natural”. However, in my experience, you need to be very experienced in using compressors to notice much of a difference. I’d worry more about the other controls first.
Compressor sounds
It’s worth noting that there were various ways of electronically achieving the compression effect with hardware electronics. Sometimes optical electronics were employed.
Without getting too technical, it basically involved the level of the signal causing a bulb to light. The higher the signal the brighter the bulb. This was placed next to a light-dependent resistor which was in the signal amplification circuit. VCAs were also used along with some other inventive techniques.
The upshot of all of this was that devices sounded different. As with lots of vintage audio equipment, these sounds and colourations became part of the “sound” that people wanted on their recordings and records. So much so, that some of this hardware has become classic” and lots of plug-ins set to emulate these classic sounds.
If you get the chance, once you have mastered compressor settings, you should experiment with different types of compressors and try to familiarise yourself with their strengths and weaknesses. Some types of compressors are better with drums and percussion and some are known for their use on vocals.
Final Thoughts
As you can see, although you can copy settings from the audio compressor settings chart, to give yourself a head start, once you’ve used these a few times, you’ll want to experiment and find out exactly what these controls do, and why you set them specifically for certain sounds.
Compression and EQ are two of the most important things to master when it comes to recording and mixing.
Unfortunately, they are two of the most difficult techniques to fully master. However, if you start with the audio compressor setting chart, they will definitely help to make things sound better.