Abbey Road RS56 Passive EQ.

The RS56 was the first parametric EQ, built at Abbey Road in the early 1950s for the vinyl cutting rooms and adopted by the recording engineers once they realised it outperformed the tone controls on their consoles. It is a passive design, which is where the smooth, unforced quality comes from. Three bands each offer four frequencies and six filter types, and it works as readily on drums, loops and synths as it does across a mix bus.