In general, most graphic EQs have between 7 and 31 bands. Professional sound-reinforcement graphic EQs generally have 31 bands, and the center frequency of each band is spaced 1/3 of an octave away from the center frequency of the adjacent bands, so that three bands cover a combined bandwidth of one octave. 2/3-octave designs (15 bands or fewer) are also common on affordable compact mixers, guitar and bass amplifiers, and other applications were less precision is required. In traditional graphic EQ designs, the center frequency of each band is fixed. For more information on Graphic EQs, please review this article.