We've seen before that iOS can be very powerful in terms of producing audio, but there's one big drawback, and it's that iPhones and iPads are still only designed to be used for one task at a time. If you want to do more than one task at a time (like combining beats with a synth, or processing and recording vocals), you're either out of luck, or you have to find an app that does both.
Until now, apparently. Audiobus is a brand new app for iOS that purports to have solved this problem, and will combine audio sources and actions