16 analog I/O on DB25 connectors, 16 AES digital I/O (DB25 breakout), MIDI I/O, wordclock I/O. Comes stock with an empty card slot, which can be fitted with one of these 16-channel cards: LT-FW (FireWire 400), LT-USB (USB 2), LT-HD (Pro Tools HD), LT-ADAT (Optical), LT-MADI. Also available as a "VT" (variable trim) version which has adjustable I/O levels via internal mini trim pots on the main circuit board.