A GRAPHIC equaliser or EQ pedal is a pretty simple effect. Just like the bass, middle and treble controls on your amp, it offers you control over the overall shape of your sound.
Rather than giving you one control for each frequency range of your tone, though, a graphic EQ splits your sound into finer ‘bands’ for more specific fine tuning. Six- or 10-band EQs are most common in guitar pedals, enabling you to hone in on a particular area of your guitar’s frequency range.
It may look a bit daunting, but a graphic EQ works exactly the same as the one on your hi-fi. The bands to the left cover bass/low mid, and the bands to the right cover the treble frequencies. If we need to explain the middle ones, you should probably take up the drums...
Each of the sliders either boosts or cuts its respective frequency, and in most cases the middle of each slider’s range is your ‘flat’ or unaffected point.
A solid EQ pedal can be used for a number of tricks: you can scoop your mids for a thrash sound; create a ‘telephone’ effect by cutting the bass and treble and boosting the midrange; or even use it as a flat volume boost by pushing all of the frequency bands equally. It’s also handy for either killing or introducing feedback onstage, or levelling out any unwanted tonal variations when you’re switching guitars.