Equalization, is the process of adjusting the strength of certain frequencies within asignal. The most well known use of equalization is in sound recording and reproduction but there are many other applications in electronics and telecommunications.

In the Pedal Board, an equalizer help shape your tone, such as this type of stomp boxes:

MXR KFK-1 Kerry King Ten Band Equalizer

[MXRKFK-1] The MXR KFK-1 Kerry King Ten Band Equalizer was designed in conjunction with the legendary Slayer guitarist. This beastly, tattoo-covered pedal has all the functions of the M-108 times 2 with its dual outputs. The KFK-1 will help you shape thrash-approved, scooped-mid rhythm tones plus create raging sustain and feedback. It'll help you wring more thunderous low-end out of your rig than you ever thought possible.

Boss GE-7 7-band EQ Guitar Stompbox Pedal

One of the handiest effects pedals we've seen. The GE-7 has seven bands ranging from 100Hz to 6.4kHz, ideal for guitar sounds, with boost/cut of +/- 15dB per band. This lets you completely control your sound and eliminate unwanted feedback, particularly when connected after a distortion effect.Exceptionally quiet EQ with silent FET switching.
The Boss GE-7 Equalizer Pedal provides 7 bands of EQ in the optimum range for guitar. It provides 15dB of either cut or boost in each selected range.

Behringer Yellow Graphic Equalizer Stomp Box EQ700

Behringer EQ700-GRAPHIC-EQ
Stomp Box, EQ

Shape your sound effortlessly and eliminate feedback with 7 EQ bands. Tackle frequencies ranging from 100 Hz to 6.4 kHz with a powerful 15 dB boost/cut per band.

MXR M-108 10-Band EqualizerMXR's M-108 lets tone-tweakers go nuts shaping their sound. This 10-band graphic EQ offers precise control over 10 guitar-centric frequencies - including individual sliders for input gain and output volume - and it also works well with bass, keyboards, or any other electric or electronic instrument. The M-108 lets you take a single-coil into humbucker territory and vice-versa with ease, not to mention conjuring anything from scooped midrange metal tones to hot lead tones. Best of all, you can continually re-invent your guitar sound with the M-108.

MXR M-109 6-band EQ Pedal

Make the MXR M-109 6-Band Equalizer your guitar pedalboard's secret weapon! You can use this compact EQ pedal to fine-tune your tone, shape wicked footswitchable lead tones, or even boost (or cut) your volume! Want to tame the artificial-sounding "quack" from your acoustic pickup, or take care of pesky feedback frequencies? Dial in natural tone on the M-109 6-Band Equalizer! This versatile pedal features six paragraphic slider controls, each with plus or minus 18dB of volume control. Get more out of your rig with the M-109 6-band Equalizer!

Boss EQ-20 EQ 10-Band Programmable EQ Pedal

The EQ-20 Advanced EQ gives guitarists, bassists, and other live performers 10 bands of programmable EQ with stellar sound quality. Physical sliders make instant EQ tweaks easy, and a straightforward Write function permits instant storage of EQ settings into nine memory locations.