I'm using my M-Audio Oxygen 61 with no problems via the camera connector. On apps that feature MIDI Learn, like Sunrizer, I have my faders and knobs controlling different aspects of the synth. I have not been able to do MIDI Learn on Garageband for iOS, but my hope is that in future updates they could include:
Time Flex and Groove Matching
More control over effects suite (reverb, delay, compressor, eq, etc.)
If Apple feels that this will bloat the price of their app, I suggest retooling the now defunct Logic Express into an iOS app and make that app the powerhouse it can be on the iPad. Hopefully not too much time passes for Apple to do that since Wave Machine Labs is deploying Auria soon (http://auriaapp.com/).
For those of us not doing music for a living, we can be pretty happy with a DAW that can rival the entry level desktop/laptop DAWs like Reaper, Cakewalk's Music Creator, Pro Tools LE, etc.
I've got a first gen iPad and I'm trying to control Streetly's Mellotronics with an M-Audio Keyrig 49.
First I learned you can't use any usb adaptor other than Apple's camera connection kit - ok.
I've now got power (after a message saying the controller required too much power), but, it's still not talking to Streetly. Do I need host software like garageband in order to source the Midi information, or can I not just go straight to an app from my controller as I'd hoped? And if so, which is simplest and lowest power drain...
... cause I don't need much, just lofi-ish stuff. I've got the 'Tron, now I just need a Theremin... (what I wouldn''t do for Steinberg's Hypersonic!).
The problem is simple, but painful; Mellotronics M3000 app does not have MIDI support.
Try your setup with other apps like Sunrizer, Casini, Garageband (those that can handle MIDI). If you need a list of apps that support Core MIDI, visit http://www.iosmusician.com/p/list-of-app-lists.html.
Sorry, but until Mellotronics upgrades its app to Core MIDI compliant you'll have to use the on-screen keyboard.