What is compression, when to compress, and why to compress
First, an analogy: Let’s imagine a city skyline with buildings varying in different heights. Everyone can enjoy the view up until some oil baron decides he wants to build a massive hotel closer to the beach, taller than any of the buildings. So tall in fact, that if he built it any higher, it would clip the atmosphere and crash to the ground. Everyone’s view is now obstructed. What a bitch. However, this architectural marvel inspires the city to build their own buildings taller, so they can also share in an extended view of the skyline.
There’s one problem. Due to the strict union of the city’s construction company, if they add to the height of one building, they have to add to the height of every single building on the skyline. So there’s only one option, they must lower (or compress) the hotel first. They cut the hotel by 1000 floors. Now that there is more headroom for the hotel, they can safely add another 1000 floors to all the buildings without any worry that the hotel will clip.
Make sense? This example described the process of compressing the loudest peaks in your track and then using the compressor’s make up gain to raise the whole track back to unity gain (0db).
Why would you want to do this? Let’s say you have your track mixed and it’s sounding good, but it’s lacking the volume you were hoping for. You look at your waveform and see that the drums in your track are punchy and crisp, but since they’re hitting unity gain, it’s preventing the rest of your track from being raised (if you did raise it, your drums would pass 0db and your track would clip). By compressing the drums, you’re now rewarded with some headroom to bring everything up a little more. Every bit counts!
Another great use for compression is if you’re working with a vocalist who sometimes gets a little too close to the microphone at times. He or she sounds great through 90% of the song, but parts of the chorus are a little too loud. A compressor (you can also think of it as an auto-volume knob) will turn down these loud bits depending on the settings.
A compressor typically has these settings:
Threshold – This sets the ceiling of when the compressor will kick in. The higher the threshold, the less the signal will be affected and vice versa.
Ratio – Once the signal passes the threshold, the ratio determines how much it’s turned down by. So for example, with a ratio of 3:1, for every 3db that pass the threshold, only 1db will be allowed to pass. Lower ratios will offer more subtle results whereas higher ratios will be very noticeable.
Attack and Release – These controls determine how fast the compressor reacts once it crosses the threshold. These controls typically use milliseconds to set the amount of time it takes for the compressor to take action once it passes the threshold (with attack) and how long it holds onto the compressed signal (release).
Makeup Gain – Once the compressor reduces the signal, you’re able to raise the output to a more optimum level (think back to the building example).
Compression is one of those things that is easy to learn, but can take a lifetime to master. With its many and subtle uses, it can help you carve out the perfect waveform allowing for maximum headroom and dancefloor pleasure. If you have anything to add or any questions and comments, feel free to post!