Equalization is a process in which the volumes of separate, narrow ranges of frequencies in a signal get adjusted, boosted or cut, so the resulting program sounds balanced, or equalized, with all the frequencies, from low to high, playing at their best volume for each instrument's timbre and tone, and the room's acoustics. You can think of multi-band EQ as tone control on steroids — instead of the high, mid, and low tone controls of a mixer's standard 3-band EQ, an outboard graphic equalizer can offer, for instance, 31 bands of control over the audio spectrum.
You need an outboard equalizer if you want finer, more detailed tone adjustments than just the treble, midrange, and bass control you get from your mixer. Here are common situations where you need an equalizer:
- Individual instrument tone – One reason to use an equalizer is to adjust the tone of an individual microphone or instrument channel to sound its best. We already mentioned how a bass control can clean up a vocal track. You can also add some oomph to a kick drum and sizzle to a high hat with some EQ adjustments on your mixer.
- Tone of a PA in a room – Another function of an equalizer is to match the sound to the space it's played in, compensating for room acoustic problems like the peaks and nulls created by reflections and absorptions. A high degree of tone control is necessary in order for a PA system to sound good in a difficult room or if it has to play in a different room every night.
- Onstage feedback control – Using an equalizer is crucial when running stage monitors. The fine control over separate frequencies lets you dial in vocal sound that cuts through the rumble and roar of a band on stage. You prevent acoustic feedback — that horrible ringing that occurs when a mic picks up its own sound from a speaker — by using an equalizer to turn down just the notes that start to ring.
A graphic equalizer is easier to use, with a control for each of its preset bands that graphically shows you at a glance what its frequency response is by its position on the front panel. Graphic equalizers generally come in 15-band or 31-band models and feature a vertical slider to control the level of each band. With a 15-band EQ you can fine-tune a PA or monitor system to sound tonally right and prevent most feedback issues. The finer resolution of a 31-band equalizer gives you twice ability to focus in on a problem and solve it without affecting the rest of the sound.