A passive equalizer with powerful sound-shaping capabilities, the RS56 Universal Tone Control was originally introduced in the early 1950s and used in Abbey Road Studios to prepare recordings for the record-lathe, as part of the process we now know as “mastering.” Later, Abbey Road’s pop engineers began using the RS56 for studio recordings because of its abilities to dramatically manipulate sound – unlike the basic treble and bass EQs found on the mixing consoles of the time. This earned it the nickname “The Curve Bender.”