Active vs Passive Circuitry

Passive

• How the Circuitry Inside the EQ Actually Causing the Changes in the Frequency Spectrum

• e.g. Pultec EQP-1A

• Only Uses Transistors, Capacitors and Inductors to Affect the Frequency Spectrum

• Passive EQ Affects the Entire Frequency Spectrum, e.g. Even when you Just Dial in the 60Hz Button in the Pultec it Affects the Entire Frequency Spectrum

• in a Passive EQ there is No Boosting at Anything, i.e. if you Boost at the 60Hz Frequency it Effectively is Cutting Every Other Frequency than the 60Hz (i.e. Makes a Bump at 60Hz Mark)

• the Boost if Effectively Happening in the Amp After the EQ Section

Active 

• Filters out Target Frequency and Causes Phase Shifts Using Opt Amp, Tubes, Transistors

• e.g. Large Format Consoles, SSL / Neve / API

• those Phase Shifts Occur Around the Target Frequency when you Either Boost or Cut it

• so in a Active EQ you Change the Target Frequency and a Little Bit Around it while the Rest of the Frequency Spectrum Outside that Range is Unaffected