Early in your career, you may see compression as this magical tool that all your favorite mixers use. In reality, though, compressors are more likely to make your mix sound worse if you don’t know how to use them properly.
Let’s assume you’ve got a solid grip on the basics: attack, release, ratio, threshold. But knowing how a chainsaw works doesn’t mean you’re ready to start lumberjacking.
Below, we've highlighted some of the most common mistakes beginners make when using compression and demonstrate how to avoid them. For each of our audio samples, we've used plugin emulations of classic compressors.
You’re Not Using the Right Tool for the Job
There are several different types of compressors, each with their own unique sound. Make sure you’re using the right one for the job.
Optical compressors tend to be very slow, smooth, and musical. The input signal is used to light up a bulb inside the unit, which triggers the compression. The louder the signal, the greater the light that hits a photocell, and the more compression is applied. The Teletronix LA-2A is the most popular optical tube compressor.
Vari-Mu compressors vary the gain of their tubes to limit the signal. They feature fixed attack/release times and have a variable ratio, applying more compression as the input signal increases. Best used for mastering, they are very good at adding glue to a mix, or fixing instruments that sound particularly thin. Famous examples include the Fairchild 670 and the Manley Variable-Mu.
FET compressors were designed to be faster and punchier than the tube models of yesteryear. They're known for their fast attack and release times, colorful tone, and ample harmonic distortion. Great for adding excitement and energy to tracks. The most famous FET compressor is the 1176.
VCA compressors have some of the fastest attack and release times. They also tend to be the most neutral compressor design. However, models like the DBX 160 and the SSL 4000 channel strip units are known for their signature punch.
Think about which type of compressor is best for the job. If you’re looking to discreetly tame transients, a VCA will do well. If you’re looking to add vintage warmth and sustain, try an optical compressor. And if you’re trying to crush something in parallel, a FET model should do the trick.
For Instance, if you want to punch up your kick drum, try using a VCA compressor like the DBX160. Listen to how the Fairchild Vari-Mu compressor adds sustain but reduces punch.
You’re Not A/B-ing Properly
Your brain is dumb. It will believe whatever your other senses tell it. If you smell charcoal, you will assume someone is grilling. If you eat something and it tastes like chicken, you will assume it’s chicken. And if you hear two signals back-to-back and one of them is louder, you will assume the louder one is better.
In order to tell if you actually made the track sound better or worse by compressing it, you need to compare it to the original—at the same level.
You can adjust the makeup gain to compensate for any volume loss. And if you use other plugins on the track, make sure each of them is properly level matched as well. Otherwise, you’ll be comparing apples to oranges.
Remember, mixing is largely psychoacoustics, and you’re just as susceptible as the listener.
You’re Compressing Too Much
Compression is tempting. Seductive, even. A little sounds good, so a lot must sound great, right? The more you turn the dial, the more exciting the track becomes. Until… it doesn’t. Eventually, it sucks all of the life out of your track. At a certain point the compression becomes audible and causes a pumping effect.
So, how do you avoid over-compression? Well, the obvious answer is to compress less, but that might not be the style you’re going for. Here are a few pointers for making your compression less audible.
Use lower ratios, like 4:1, 2:1, or even 1.5:1. They’re more subtle.
Don’t compress too hard. Try to stick to 3dB-6dB of compression.
Use more compressors that do less compressing. Instead of knocking off 6dB with one compressor, try reducing the signal by 3dB on two different compressors. This is called serial compression.
Use parallel compression. Sometimes smashing something to smithereens sounds good! But you’ll lose the clarity unless you do it in parallel and blend the signals together.
Use bus compression. Bus compression helps glue multiple tracks together. And it also adds another layer of serial compression.
Your Attack Time Is Too Fast
A lot of beginners assume fast attack times will make a track sound more exciting. It makes sense. Fast things are generally more exciting than slow things. Plus, fast release times help add punch, so it’s an understandable mistake.
But the truth is, slower attack times allow the full punch of a transient to come through before the signal is compressed. If your attack time is too slow it can completely miss the transient all together. Start with the slowest attack time and slowly increase it until you start to lose punch.
On the other hand, if you set your compressor too fast you can actually shave off the beginning of a transient. While that can make things sound tight controlled, it doesn’t add any punch or energy.
Your Compressor Isn’t Breathing
Audible compression is usually a bad thing. You want your compressor to “breathe" with the song to make it feel more natural and musical.
For instance, say you’re compressing a snare. Start by setting the release time as fast as possible. As the snare is hit, the compressor needle jumps up to show 3dB of compression. Since the release time is so fast, the needle immediately drops back down to 0. The goal is to make the compressor react in time to the music, just like the rest of the instruments.
Slowly decrease the release time until the needle just barely reaches zero before the next snare hit. If you set it correctly, the compressor needle should be jumping up and down in time with the music, and the compressor will be “breathing."
You’re Not Listening
So many of us are guilty of this one. We’ve all added a compressor to an empty channel strip without even listening to the track. You “know" the kick needs compression. You “know" an 1176 will sound good on that vocal. You “know" the attack and release times should be this or that. Or, even worse, you’re relying on presets alone.
Remember, plugins do not equal progress.
There are no one-size-fits-all solutions in mixing. Every move should be reactive to the situation. It’s not enough just to listen, you need to analyze what you’re hearing. What do you like about this track? What do you dislike?
As always, remember to use your ears, and trust your gut.
Audio samples of the song “Executive" provided courtesy of Bleed American. Their new album It Probably Isn’t is out January 5, 2018.