External Input / Envelope Follower (Vintage Edition)

Module A-119 (External Input / Envelope Follower) is designed to allow external audio signals to be integrated into the System A-100. It comprises a pre-amp, envelope follower, and comparator.
The pre-amp has two inputs: an unbalanced input for line level signals, with a gain factor of from 0 to 20, and a balanced input with a gain factor of from 0 to 500, for insertion of low level signals, for instance from a microphone or electric guitar.
The Envelope Follower reads the signal level of the input, and puts out a proportional voltage as an envelope at its own output.
The comparator generates a gate signal whenever the input goes above an adjustable trigger threshold.
Three LEDs help you keep track of overload, the envelope, and the gate signal.

http://www.doepfer.de/a119.htm