What ten bands actually change
A graphic equalizer splits the spectrum into fixed bands and gives you one fader for each. This one uses ten, centered at 31, 62, 125, 250 and 500 Hz and at 1, 2, 4, 8 and 16 kHz. Each slider drives FFmpeg's equalizer filter as a peaking band one octave wide, so moving the 1 kHz slider affects roughly 700 Hz to 1.4 kHz with the most change at the center and a smooth fade on either side. Neighbouring bands overlap, which is why lifting two adjacent sliders by 3 dB gives a bigger lift between them than either slider suggests.
Every band can be moved by 12 dB in either direction. In practice, most corrections are far smaller. A 3 dB change is clearly audible, 6 dB is a strong statement, and 10 dB or more is a special effect, like a telephone voice made by cutting the lows and highs and leaving the middle.