Compression controls the dynamic, or the relationship between loud and quiet parts of sound. Learn about how compression can help your musical expression!

This interview originally appeared in She Shreds Magazine Issue #14, released February 2018.

A few years ago, I kept running into a frustrating situation. My band would be heavily rocking with distortion pedals engaged. But when it came time for a clean part of the song, I’d disengage my distortion and my clean tone would become lost within the swell of the rest of the band. I knew I needed to find a better way to control my dynamics. That was when the MXR Custom Comp compression pedal pulled my distant riffs back to the surface. My clean tone became bigger and bolder, earning a proper seat at the table amid the loud amps and drums. My quiet notes were loud and my distorted notes weren’t too loud.

This is what compression does: it shapes the dynamic—the relationship between the loud and quiet parts—of a sound. Compressors can exist as guitar pedals, studio equipment, or mixing tools in recording software.

As a live sound engineer, too, compression is one of my most trusted companions. A vocalist with a wide dynamic range could be softly whisper-singing during the verse, but come the chorus they might belt or scream into the microphone. If I simply turn the vocals up so the audience can hear the quiet parts, this could get me in deep trouble when the loud chorus arrives. Instead of anxiously keeping my hand on the volume fader and adjusting throughout (a.k.a. “riding the fader”), I can use a compressor to do the dirty work of controlling that dynamic range for me.

Here are some other scenarios where you might want to utilize a compressor on bass, guitar, or vocals. (I’ll explain some of the terminology after.)

One of the simplest compressor pedals out there, the MXR Dyna Comp, has just two knobs: output and sensitivity. The sensitivity knob represents the amount of compression being applied. The more you increase sensitivity, the more your loud and quiet sounds will be squeezed together; think wrapping an ankle sprain with a bandage. The output knob allows you to raise the final volume of the compressed signal in order to win that overall loudness back. The two controls work together to give you a well-rounded, tighter, more consistent signal.

Here’s a breakdown of the most common parameters you’ll see on a compressor pedal:

Input (a.k.a. Level)

The volume level of your signal BEFORE compression

Output (a.k.a. Level)

The volume level of your signal AFTER compression

Threshold

The level of your signal at which compression kicks in

  • lower threshold = more of your signal gets compressed
  • higher threshold = less of your signal gets compressed

Ratio

The intensity of compression in response to threshold, often containing these settings:

  • 1:1 = no compression
  • 2:1 = gentle
  • 3:1 = moderate
  • 7:1 and above = strong / brickwall limiter
  • lower ratio = subtler compression
  • higher ratio = more noticeable

Sensitivity

A combination of ratio and threshold

Attack

The amount of time it takes for compression to begin after the signal reaches the threshold

  • faster attack = smooths and rounds out the beginning of the sound
  • slower attack = preserves the sharpness/cut of the beginning of the sound

Release (a.k.a. Sustain)

The amount of time it takes for the compressor to disengage/let go

  • faster release = better for single-note playing
  • slower release = better for chords and long sustained notes

If you’re going for a natural sound, beware of over-compression. Turning the sensitivity and ratio all the way up, or the threshold all the way down, can squash the dynamics like a pancake. Major radio stations actually thrive off of over-compression, which is why every song you hear on the radio is always the same perceived volume level. (It’s also why every word spoken by a DJ is so obnoxiously loud.) 

To really learn how compression works, pair up with a friend and have one person tweak each knob while the other plays. Listen and take note of what happens. When it sounds good to you, you’re done. In fact, you should be very compressed with yourself!