The list IO of 4ms is an interface module for feeding in and feeding out audio signals with optical level control. The upper half is dedicated to the preamplifier (PreAmp), which prepares external signals for the modular level and can also energize them powerfully. The lower section leads the signal out of the modular system (line output) and transforms it into a line level, alternatively two headphones can be connected to the two sockets.
The preamplifier and line output are both stereo, each with a volume knob and a convenient LED chain for visual indication of the set level. On the back there is a socket bar for Daisychain operation, in order to be able to operate a Listen4 or Listen4 Quarter in a group.