The 442 I/O (MH031, 4x4) is the audio interface used in the original Pro Tools system (sometimes called Pro Tools II). It can also be used with an Audio Card (SA4) in a PTIII system to provide 4 additional inputs/outputs. (Requires a TDM single piggyback. Doesn't add DSP or voices.)Analog Input/Output: Active Balanced XLR (pin 2 hot); +4dB level.Analog I/O Impedance: Differential 200kohms, single ended 100kohms (input); 22ohms per leg (output).Digital I/O: 16-bit, Active transformerless inputs (AES balanced, S/PDIF unbalanced), transformer coupled outputs (both).AES pinout: Pin 1 gnd, pins 2 & 3 balanced signal (not polarized); impedance 110ohms.External Sync: 256x sample rate (Super Clock) in/out, about 3 Vpp, BNC connectors.NuBus Card Connector: 50-pin, SCSI2-type female.Sample Rates: 44.1k or 48k.Analog-to-Digital Converters: 1 Bit, Delta-Sigma, 64x Oversampling, 16-bit output.Digital-to-Analog Converters: 18-bit, 8x Oversampling.Operating Level: +4 dBu nominal (factory calibrated at 14dB or 18dB headroom).Maximum Levels: +26dBu (input), +24 dbu (output).Frequency Response: 20Hz - 20kHz +/-1db.Signal-to-Noise Ratio: > 93 dB A/D, > 108 dB D/A (A Weighted).THD + N: .005% A/D, .003% D/A.Power requirements: 100, 120, 220, 240 VAC, 10-60Hz, 16 watts, auto-switching. The power supply is a Skynet model SNP 3034Dimensions: 1U external rack mount device; 19" x 8.5" x 1.75".