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What’s the difference between a compressor and a limiter?
What do they have in common?
Discover how they are crucial for dynamics and loudness.
Compressors and limiters both have important roles in audio production. But although their functions are similar, their uses are actually very different.
Sure, they are both gain reduction tools, simply ‘turning the volume down’ when necessary. But the differences between the two are important and something you need to know for getting a proper handle on dynamics and loudness.
Limiter vs Compressor: What’s The Difference?
A limiter and compressor both work using the same principles. In fact, a limiter is a compressor but with a fast attack time and a high ratio (usually around 10:1 or more). Both have their place in audio but it is important to know which to use and where.
As always, one of the best ways to learn is to test and compare them, crank the settings to the extreme and listen to how they differ. If you are new to compression then check out our favourite free compression plug ins.
What Does A Compressor Do?
Simply put, a compressor stops the audio from getting too loud. To do this, it reduces the volume of incoming audio once the sound crosses a certain ‘threshold’ in decibels (dB). Quite often, the signal is then boosted with ‘makeup’ gain to create a louder result.
Compression itself has a myriad of uses in the mixing and mastering process and the result you get will vary between compression units and plug ins.
There are a number of controls available to us on compressors which change the character of the overall gain reduction. We won’t get too bogged down in compression techniques for your mixes (for this, check out our article on how to compress properly), but we will go into how a compressor works as a tool.
‘Threshold’, ‘ratio’, ‘attack’ and ‘release’ controls are the most crucial components on compressors. Your plugins may have other settings, but these are all we need for understanding what a compressor does.
Threshold and Ratio
A compressor operates by setting a threshold, or a certain point at which compression will kick in, measured in decibels (dB). Once the signal passes this threshold, the volume of the track is reduced by an amount in dB designated by the ratio setting.
For example a 2:1 ratio decides that a signal that is 2dB over the threshold becomes 1dB over, and a signal 4dB over becomes 2dB. A 4:1 ratio is twice as “strict” meaning a signal 4dB past the threshold will be reduced to 1dB and so on.
A higher ratio equals a greater amount of compression. Once you start entering a ratio of 10:1, this is typically considered as ‘limiting’. Brick wall limiting cranks the ratio even harder, along with an even faster attack time for that ‘choked’/’pumping’ sound.
Attack and Release
A compressor will also have ‘attack’ and ‘release’ controls, similar to an envelope on a synth. Attack determines the time to reach the compression values, while Release determines how quickly it reverts to an uncompressed state, respectively.
A fast attack will sharply squash any transients while a slower time offers a punchier, percussive quality that allows the transients to pass through unaffected.
A fast release adds more of a pumping sound whilst a slow release is more transparent.
A limiter is still a tool for reducing the gain of a signal but it tends to be much more ‘strict’. For this reason, a limiter typically doesn’t offer as much control over the sound as a compressor and so it becomes less of an artistic tool.
You usually won’t find an attack, release and ratio setting on a limiter. They become ‘under the hood’ controls that are fixed to certain settings. Ideally, the attack and release will be quick and transparent and the ratio will be 10:1 or higher.
The reason being that a limiter is built to completely stop an audio signal at a certain level. Where a compressor allows some signal to pass the threshold and then be turned down, a limiter will stop the audio completely after a certain volume.
Both are utilized to reduce gain but a limiter will be much more aggressive in doing so, due to the significantly higher ratio.
Often a limiter is as simple as having a ‘gain’ and a ‘ceiling’ dial, the ceiling being the point that the audio stops. This is typically just above where your loudest drum hits are – enough to trim out fleeting peaks without ruining overall dynamics.
Should I Compress Or Limit? Here’s When To Use Each
So in short, a compressor will gradually reduce the volume of an instrument once it passes the threshold, whereas a limiter will not allow any audio to pass beyond this ‘ceiling’. A compressor is a lot smoother, a limiter is a lot more aggressive.
As we’ve mentioned, a compressor tends to be more ‘artistic’. For example, a compressor can simply tame loud spikes in volume or rather musically add punch to percussive instruments. Compression can even create overdrive effects with fast enough attack and release times.
Each compression unit will have its own unique characteristics and some work better than others in different situations. It is not uncommon for a mix to feature several compressors on different audio tracks.
It is also not uncommon to use more than one compressor on a single instrument if the volume is particularly unruly.
A limiter, on the other hand, is less often used as a mixing tool and is more likely to be used in the mastering stage. Ultimately, there are no rules though.
The reason being that when it comes to mastering, a track needs to appear louder to compete with commercial standards. The gain can be increased incrementally to add volume to the track whilst the ceiling will stop the signal clipping or exceeding a crucial level. This is extremely important when adhering to streaming service’s loudness guidelines. Loudness penalties are real, and each streaming service has its own set of rules.
Quick Compression & Limiting Tips
Compression will remove dynamic range from your tracks. Generally this is a bad thing but when used tastefully it can really enhance a mix.
Sometimes, parts have too much dynamic range. Raw recordings typically fluctuate in volume in a way that is detrimental. Microphones are very sensitive and performers can get carried away moving around.
Sometimes you just want a sound to be big and bold. You’re not correcting a performance, just exaggerating what’s already there.
Using compression is about finding the sweet spot. Removing dynamic range can add punch and character to a mix however over-compressing can easily ruin it.
It’s also important to really consider attack and release. A quick attack will sharply tame a transient which can remove the life and punch from percussive sounds. On the other hand, if the attack is too slow the compressor will kick in too late and sound weird.
With limiting you need to think about your headroom. Simply turning up the gain may sound great at first as we tend to favor loud signals when making comparisons. However, you then run the risk of squashing your sound and draining it of musical dynamics if you are not careful.
Make sure the limiter is not working overtime. It should be kicking in occasionally to trim unwanted peaks but not constantly squashing the sound. Too much gain reduction can result in a pumping effect as your audio is constantly being pushed down in volume, sounding odd and unpleasant.