Audiobus not compatible with Garageband on 4th gen iPod Touch?
The latest version of GarageBand, version 1.4, released March 20, 2013, incorporates support for Audiobus. I looked up the specifications of this version in the App Store under the "Whar's New" heading. I'll paste in the description.
• Play and record music apps supported by Audiobus directly into GarageBand*
• Turn off grid snapping to get finer control over region and note editing
• Fixes an issue that resulted in feedback while connecting 3rd-party audio accessories into the headphone/microphone jack
* Requires iPhone 4S, iPod touch (5th generation), iPad 2 or later. Audiobus requires a separate purchase.
It seems that the problem is that the version 1.4 update of GarageBand Audiobus support applies to iPhone models 4S and later, iPod Touch models 5th generation and later, and iPad models 2nd generation and later (which includes the iPad Mini). So Audiobus should work on your iPhone 5, but not on your 4th generation iPod Touch. This appears to be a function of the requirements of the app that is running Audiobus, but basically all the devices that are listed use dual core processors. The dual core processors of the iPhone 5 and the 4th generation iPad are delivering about 2.5 times the performance of the 5th generation iPod Touch, which is the device at the bottom end of the Audiobus compatible devices. From Audiobus forum posts, a user with a 4th generation iPod Touch said it was possible to run some Audiobus compatible apps, especially by breaking down the steps, but that some synths and apps were just more CPU intensive, and that it didn't take much to produce stuttering, skipping notes, distortion, and hang the app, requiring a device reboot. Best performance came from the 4th generation iPad, followed by the iPhone 5, and then the 3rd generation iPad.