EQ (Equalization)
A process for boosting or cutting specific frequency ranges to shape a sound or fit it into a mix.
EQ — short for equalization — is the tool every mixing engineer reaches for first. Every sound is a stack of frequencies, from the deep sub-bass below 60 Hz to the brilliant air above 10 kHz. EQ lets you turn those frequencies up or down independently, so a muddy bass guitar can lose its 250 Hz buildup, a dull vocal can find clarity around 3 kHz, and a harsh cymbal can stop drilling into your ears at 6 kHz.
There are three common EQ types. A parametric EQ gives you a fully adjustable band — pick the frequency, the gain (boost or cut), and the Q (how narrow or wide the band is). A graphic EQ gives you a fixed set of bands you can only move up or down. A shelf EQ pushes everything above (or below) a threshold up or down together, useful for adding "air" at the top of a vocal or "weight" below a kick drum.
Mixing engineers often work subtractively before additively: cut what doesn't belong before boosting what does. A muddy snare usually doesn't need more crack at 5 kHz; it needs less mud at 250 Hz. Train your ears to identify problem frequencies before reaching for a boost, and your mixes get cleaner fast.