X Air XR18 and X Air X18 Both mixers have USB ports (type B) so they can be connected to a computer using a USB cable for multi-channel audio and MIDI recording. Up to 18 audio channels can be simultaneously recorded, and 18 channels are available for playback. The mixer application allows assignment of channels for recording and playback. 16 channels of MIDI I/O can also be transmitted on the same USB connection.X Air XR12 and X Air XR16 Both mixers have USB ports (type A) so they can accept USB flash drives for file storage, stereo recordings and playback. Neither the XR12 nor the XR16 can provide multi-track recordings.