The API 550 from Waves is a plug-in developed in association with API that models two classic API equalization modules. The API 550A module is modeled on the legendary late ’60s hardware and provides reciprocal and repeatable equalization at fifteen points in five steps of boost, divided into three overlapping ranges. The high and low frequency ranges are individually selectable as either peaking or shelving, and a band-pass filter can be inserted independently of all other settings.The API 550B functions both as a problem solver and a sweetening device, and provides four overlapped EQ bands with seven switchable filter frequencies spanning up to five octaves per band. “Proportional Q” automatically widens the filter bandwidth at minimal settings and narrows it at higher settings. The EQ can undo previous processing, or even perform reverse tonal modifications.