The ATUC-50CU rack-mountable control unit can power and control up to 50 ATUC-50DU discussion units. Up to three control units may be cascade-connected via Cat5e (or better) cable. This cascade-connection thus enables the use of up to 150 discussion units in one system. The ATUC-50CU features four balanced outputs and one unbalanced output, plus left/right AUX RCA inputs, two mic/line inputs, and two interpretation return inputs to provide simultaneous interpretation feeds in addition to the floor language feed. The ATUC-50CU is equipped with an audio recorder that can record MP3 or WAV files of 2 GB or less onto a connected USB mass storage device (2 TB max. storage capacity). When the 2 GB limit is reached, a new file can be created to continue recording. Up to four channels are available for recording WAV files; up to two channels are available for recording MP3s.