M-Audio MIDISPORT 4x4 Anniversary Edition | 4-in/4-out MIDI Interface (64x64 Discrete Channels I/O via USB) 4-in/4-out MIDI interface (64 discrete MIDI input channels, 64 discrete MIDI output channels) Connection and power via USB, requires no external power supply Class-compliant operation under Windows XP, Windows Vista and Mac OS X, no additional drivers required MIDI activity indicator for each port Compact and lightweight for mobile or desktop use