While the compressor is an unbelievably powerful music production tool, it's also one of the most misunderstood by entry-level engineers. Together with EQ, compression is one of the most essential factors when creating a good mix. The key word here is dynamics, since this tool basically hands you control over the dynamic range of a track. The dynamic range describes the volume difference between the quietest and loudest parts of an audio recording, and that applies to every single track that makes up the production. So, if you're working on a song with ten, twenty, or even more tracks, then all of those individual elements are probably battling it out for a space in the mix. It's here that a compressor can really help things out.
Using Audio Compressors & Limiters
A compressor can be used to reduce the dynamic range of audio. In practice, this means that the loudest parts of the audio are pushed down so that the difference between the louder and quieter parts is narrowed, resulting is less dramatic volume peaks. From there, you can turn up the volume of the compressed track, making the quieter parts louder while the loudest parts still sound quieter. Applying this to most, if not all of the tracks, results in a more cohesive total mix and a more polished product. When it comes to limiters, they're usually applied to what's referred to as the 'master' or 'stereo bus' which is the total mix of all the tracks. Limiters are also types of compressors set at a really high ratio, so the output level can be set so it doesn't rise above the 0dB level and doesn't get distorted. Limiting is an essential step of the mastering phase.
Threshold
The threshold (or damping level) of a compressor sets the part of the audio that you want to compress, basically by dictating the parts of the audio that need to be quieter.
Compression Ratio
With the ratio setting of a compressor, you dictate how much of the signal is treated with compression. So, the higher the ratio, the more compression is applied to the audio. The ratio is indicated in standard mathematical ratios, where a 1:1 ratio setting applies no compression; a 2:1 ratio setting applies compression whenever the audio reaches 2dB above the threshold and reduces it to 1dB over the threshold. This means that, if the audio were to rise above the threshold by 10dB, then the audio level is compressed and reduced to no more than 5dB over the threshold.
Attack
The attack sets the reaction speed of the compression. So, how fast the compressor responds when the incoming audio signal rises above the set threshold. The attack is measured in milliseconds.
Release
The release sets the time the compressor takes to return to 'normal' when the audio has fallen back below the threshold. The release is also measured in milliseconds.
Software or Hardware
In this department, you'll find an array of hardware compressors that are the physical pieces of equipment you see in most professional recording studios. But, if you're an entry-level engineer building a little studio at home, then it can be more practical to use software-plugins. These software-based compressors can help you learn how compression works and what it can do for your mixes. Some sound engineers and producers swear by hardware-based compression, and as you gain experience, you might feel the same. If you need a compressor for a live venue and you're just starting out, then it can be worth looking at a mixer that features a built-in compressor on every channel.
Frequently Asked Questions About Compressors & Gates
What does a compressor do?
An audio compressor reduces the difference between the quietest and loudest parts of a track. This way, the dynamic range (the volume differences) is reduced and there are fewer volume peaks.
What's the best audio compressor?
This is a question of taste. While some audio engineers prefer analogue, vintage compressors, others will swear by their plugins. It can also depend on the specific instrument you're working with and which compressor will best match it.
What is a noise gate?
A noise gate interrupts and mutes an audio signal as soon as it falls below a certain level. This is so that any unwanted, relatively quieter noises can be removed.
What's a de-esser?
We also have a range of de-essers included this section, which are compressors or limiters that only compress the frequency if there are harder vocal noises like 'S' detected, rounding them off and making them sound less harsh.
What's a limiter?
A limiter is a type of compressor that applies a really strict limit on the audio level, making sure that it can't peak above a specified volume.
