500series

500-series is a modular audio processing format used in recording and broadcast studios. It originated as a compact solution for mounting microphone preamps, equalizers, dynamics processors, and other analog processors in a single frame. The name derives from the approximate width of each module (about 1.5 inches) and the common 19-inch rack footprint; frames designed to hold these modules are often called lunchboxes.

In operation, individual modules slide into a frame that provides a shared backplane with power rails and a signal bus. The frame connects to a dedicated power supply, and power, ground, and audio signals are distributed to all installed modules. While there is no formal standards body, the industry has settled on a broadly used interface and electrical characteristics that allow intermixing modules from different manufacturers.

Typical modules include mic preamplifiers, equalizers, compressors, limiters, de-essers, and other character processors. The modular approach lets engineers tailor a signal chain by combining several units in a single frame; multiple frames can be used for larger studios or more extensive processing racks.

Advantages of 500-series include a compact, portable, and cost-efficient route to a substantial analog processing setup, with the ability to swap modules as needs change. Limitations include power budgeting within frames, potential noise and crosstalk between modules, and the requirement for compatible power supplies and frame hardware.

The 500-series ecosystem is broad, with products from many manufacturers and a strong presence in professional studios as well as serious project environments.