The iPad has become an incredibly powerful and useful tool for musicians with some amazing apps for simulating guitar amps and effects and to multitrack record with. The iTrack Dock is a professional iPad Audio Interface from Focusrite, I use a Focusrite Scarlett 2i4 interface for my mac and it is excellent. What Focusrite have done is to make a solid professional dock to place the iPad into that has digital conversion at up to 24-bit, 96kHz sampling – and what’s more, it powers and charges your iPad at the same time. The iTrack Dock has Focusrite mic preamps plus two line inputs and an instrument DI, independent stereo monitor and headphone outputs, and a USB port for class compliant MIDI instruments and controllers.

http://global.focusrite.com/ipad-audio-interfaces/itrack-dock