Zapco analog processors are legendary for both sound quality and reliability. Zapco processing started in 1978 with the famous PEQ, 9 band, dual channel control, preamp EQ. With balanced inputs, high voltage outputs, and military grade internal components, the PEQ was the first true Sound Quality EQ for the car. The PEQ was followed a few years later by the Zapco PX. The PX was the first parametric EQ for the car. With high voltage inputs and outputs, an 18dB electronic crossover, 4 parametric E...Q bands, and a noise free remote power supply, the PX became the competition EQ for the 1980s. (Zapco.com)