Compression, as you may imagine, comes in many different flavors. Below we take a quick look at the different types of compression methods you'll work with as a music producer.
1. Downward Compression
This is the type of compression that most people refer to when they say compression in a studio setting.
Downward compression reduces the level of signals which go over a certain set threshold. This means the dynamic range is reduced by bringing the peaks above the threshold down.
2. Upward Compression
Upward compression, as you may have guessed by now, does the exact opposite of downward compression.
This type of audio compression increases the level of sounds which fall below a certain set threshold.
3. Parallel Compression
Parallel compression is a type of parallel processing which allows you to both preserve transients and dynamics while at the same time getting more of the consistency or punch which comes from hard compression.
This means the original signal is split into two or duplicated and each channel is then processed independently. In most cases the main signal is left un-compressed while the duplicate channel is compressed heavily. The wanted result in the mix is then achieved when you blend the two channels together.
4. Side-chain Compression
A compressor with a side-chain input allows you to trigger or control the compressor's reaction via an external signal which in most cases will be an audio signal from another channel.
This means you can use your kick sound to duck your bass or synth, for example. This results in a slight decrease in level on your bass or synth each time the kick hits, which makes the kick cut through better. It can also be useful in avoiding frequency clashes as you remove potential problem frequencies by lowering the level.
If you've not heard side-chaining in action, you've not listened to dance music. It's everywhere! At the more extreme settings it sounds like the synth or bass pumps in relation to the kick. Believe me, you know it even if you don't know you know it. ;-)
This type of audio compression isn't just limited to dance music. Used subtly it's useful in many different mixing and music production scenarios.
5. Multiband Compression
Multiband compression is frequency-specific audio compression. This type of audio compression, as the name suggests, splits the incoming signal into different frequency ranges or bands. This means you get independent control for each band. So, you can compress each band with different compression settings or only compress certain bands while leaving others unaffected.
A typical use, for example, would be where you want to even out the mid-range of an instrument with compression but don't want to compress the lows. Multi-band compression can substitute for EQ as it's a way to control levels of specific frequencies in your spectrum.
6. Mid-Side Compression
Mid-side compression works by splitting your stereo signal into a mid and a side signal. You can then compress or not compress the mid and the side signals separately before you combine the two signals back into a full stereo image.
This is useful in many instances. Say you have a stereo drum track and you want to compress the kick while leaving the overheads alone. Slap on a mid-side compressor, set it to mid, set your compression, set it back to stereo and done.
How about leaving the kick alone and adjusting the dynamics of the overheads instead? Same process as above but work on the side channel instead of the mid channel.
A Limiter is a compressor with a very high ratio setting. So, once you set your compressor's ratio to 10:1 or above you're in the land of limiting.
Brickwall limiting is when you set your ratio very high and have a very fast attack time too. Can anyone say Loudness Wars? ;-)
Limiters are useful in any scenario where you want an absolute ceiling where no signals may pass. This is why you'll often find a Limiter at the very end of a mastering chain. Limiters are however useful in other instances, like when you want to squash the life and dynamics out of a EDM bass on a parallel channel for example.
A leveling amplifier is similar to a compressor or limiter in that you use it to reduce the dynamic range of an incoming audio signal. The main difference is that the ratio, attack and release are set in a leveling amplifier. The other difference is that it automatically adjusts the gain to make-up for level lost to dynamic range reduction.
Worth a mention since traditional de-essers use compression to reduce specific frequencies over a certain level from an audio signal. The most common use is therefore to remove sibilants like sharp s-sounds from vocals.
The compressor in this case reacts only to a narrow band of frequencies, usually in the 5-12kHz range dependent on the vocalist. These frequencies are used as a trigger to duck the entire signal when they cross the threshold. Smooth!
Now that we've taken a look at the main types of compressors available, the main audio compression controls and the different types of compression you'll use, it's time to take a look at some compression techniques and practices you can implement to step up your compression game to pro level...