The presence control is a knob found on guitar amplifiers that is part of the power amp section of the amp. Unlike the EQ and gain controls, which are part of the preamp section of the amp, the presence control operates as a "high-frequency shelving boost". This means that it can increase high frequencies but not decrease them. The presence control directly adjusts frequencies above the treble control, but it also changes frequency roll-off when adjusted. This means that the presence control can change the effect of the treble knob to sound like a peaking, rather than a shelving, filter because it causes the treble frequencies to boost into a peak. Increasing the presence control decreases high-frequency-only feedback in the power amp, which makes the amp distort more easily for higher notes. It also decreases the amps ability to precisely control the actual speaker cone at high frequencies, which makes the amp sound wilder and raspier in a way that the treble control knob isnt capable of. The presence control is usually interactive with the other EQ controls, and the effect of the presence control depends on the tone youre after, your amp, its speakers, the guitar and effects you play, and so on.