If you've ever seen the BookEndz docks for MacBooks, or Metric Halo's Mobile IO, you'll understand the IO Dock concept. It's a wedge-shaped stand, holding the iPad in landscape format, made from black plastic, with four LRFs (little rubber feet) on the bottom to keep it from sliding around. A dock connector lurks within, so when the iPad is pushed into place it's charged (the IO Dock requires mains power). But more meaningfully, it can talk to the IO Dock's physical inputs and outputs—and there are a fair few of those: 5-pin MIDI in and out, USB MIDI, master volume control, 1/4" headphone output with separate volume control, left/right master outputs on balanced 1/4" jacks, left/right combination inputs giving balanced 1/4" or XLR connections, with independent volume controls, footswitch input and composite video out. Alongside these connections are switches for power on/off, guitar or mic/line level input, direct monitoring and mic phantom power on/off. Needless to say, that's an impressive list for something that hooks up to an iPad.
The IO Dock works with iPad 1 or 2, and ships with a removable adaptor for the slimmer iPad 2; lift the latch in the centre to slide the adaptor out. When it's 'loaded,' the iPad is gripped securely, with the IO Dock's surround covering three edges of the device. The iPad's top edge is exposed, but there was no suggestion that it'd fall out, even at extreme angles. Despite the tight grip, there was no marking or scratching of the iPad. (There's no way an iPad with a case will fit in the IO Dock.)
I connected the IO Dock's main outputs to my powered monitors, and ran a few music apps, including the luscious Animoog. As a straightforward audio output, I wouldn't say it subjectively sounded better or worse than taking a cable straight out of the iPad's headphone jack, but I did enjoy the convenience of using 1/4" jacks to make the connections, as well as using that physical master volume knob on the side of the IO. The Dock's headphone output jack also has its own level control.
I then plugged a Fender Telecaster into one of the input jacks, switching the level selector to Guitar and adjusting the gain control then ran it into GarageBand's guitar amps. There was easily enough volume, and was noise-free unless pushed to ridiculous extremes. I also tried a '76 Jazz Bass—no problems hearing that either. Incidentally, Amplitube, another popular guitar app, doesn't work with the IO Dock because it looks for a signal coming in through the device's headphone jack.
Anything I say about sound quality will be subjective; the IO Dock inputs are fine, and certainly good enough for the intended use. I haven't tried the Apogee Jack guitar accessory, for example, but knowing Apogee gear, I can guess that'll be a device that pushes iOS sound quality to the max. However, it has one thing to do, and costs more than half as much as the entire IO Dock, which can handle a lot of other functions. If you really only need a specialized guitar input, buy the Jack instead.
After guitar-time I dug into the old-school box and pulled out a pair of MIDI cables, which I used to connect an M-Audio Venom synth to the IO Dock. I used the Venom's keyboard to trigger notes on a few apps, including GarageBand, Xenon and iSequence, and then sent MIDI out to trigger the Venom's sounds and change control parameters, from the MIDI Touch app. The IO's USB MIDI port sends and receives MIDI notes, controllers and sync data, between the docked iPad and music software running on a computer (though it doesn't carry audio, or sync or charge the iPad). The Dock appears as a class-compliant USB MIDI device in your favourite DAW software. I tried it with Ableton Live, and it was a total no-brainer to send notes from a MIDI clip into apps on the iPad.
All of the other iOS music interface hardware available involves single-function devices, offering guitar or bass in, microphone in, or MIDI in/out connections. The IO Dock is unique in combining all of these connections—so far (funny how often you need to say "so far" in iOS product reviews).
It's not strictly a pro audio piece, but it's debatable how much effort and expense should even go into something that'll be obsolete in a year or two. It is, however, an incredibly useful device that will make all the difference to an iPad music setup, and the price is very fair; it's a much better way to live than having a bunch of separate interfaces and cables knocking around and hanging out of your device's headphone jack.
The ability to get that much in and out of the iPad dock connector is a tribute to Apple's forward thinking. I believe in the iPad and its successors as the future of electronic music production, and the IO Dock makes it all a bit easier to achieve. The IO Dock will be great as the basis of an iOS home/mobile studio, and as a live performance solution for anybody who needs "proper" audio and MIDI connections.
Ease of use: 4/5