The API 550b is a continuation of the EQ that played a major role in the history of music recording.
The API 550b provides exactly the right number of controls. Its four EQ bands are overlapped significantly to aid in dual roles as problem solver and sweetening device with each band offering seven switchable filter frequencies that span four-to-five octaves. These frequencies, purposely selected to be musical rather than numeric, were selected by an experienced "who's who" list of the industry's most proficient engineers.
• Four bands of our famous sounding equalization
• Each band offers seven API selected frequency centers
• Reciprocal and repeatable filtering
• 12 dB of boost/cut per band
• EQ band 1 and 4 offer shelf/peak switching
• "Proportional Q" narrows filter Q at extremes
• Traditional API fully discrete circuit design
• High headroom +30 dB clip level
• Re-issue of 1967 API 550 EQ with an extra band