I tried garageband with the hdmi adapter and only the video is transmitted to my tv. Audio is still coming from the ipad. Can someone else test this for me?
Found the answer on Apple's support page:
"When mirroring via HDMI with the Apple Digital AV Adapter, apps cannot simultaneously record and transmit audio. Since both iMovie and GarageBand feature audio recording capabilities, audio transmission over HDMI is disabled. Audio can continue to be monitored through the stereo headphone jack or iPad built-in speaker."