Single band parametic equalizer

The BOSS SP-1 Spectrum was an effect that boosted a select band of frequencies, so that instruments with a tendency to be “muddy”—such as electric bass—could be brought out in the mix. But the SP-1 also proved to be very popular among keyboard players, who paired it up with electric pianos such as the Fender® Rhodes.

http://www.bossus.com/go/boss_classics/sp1.html