A Mackie trade name for equalizer circuitry employed in their Onyx mixer series. The name refers to Cal Perkins, a veteran Mackie engineer who had previously done work for Marantz, JBL, and Fender. Perkins started with the Wien Bridge circuit topology – a design inspired by the hallowed “British” consoles of the ’60s and ’70s. This design essentially trades boost/cut capability for a wider, highly musical Q filter. He then specified capacitor and resistor values that would give Onyx mixers an extra 6dB of control (+15 dB) without excessively narrowing the Q filters. Perkins also employed combining filters for minimum phase shift. The result is very musical EQ that provides a wide-ranging yet natural sounding boost or cut.