Open Music App Collaboration (or OMAC) is a set of features that music apps should implement so that they can be linked together via MIDI and run at the same time, in sync with each other. So far only a handful of apps support this, but the number is growing steadily. These features include:
Please see the Compatible Apps page.
While it is exciting to finally be able to run several apps together and control them from a single app, there are limitations on how many apps can be run at the same time. The iPad is not a desktop; CPU power is still fairly limited compared to what can be accomplished on real computers. This fact is often overlooked because the iPad and iPhone typically only run one or two applications at once. In real world scenarios you may only be able to get between 3 and 5 applications running together depending on which apps you are using. Each app consumes a different amount of processing power. You’ll know when you’ve hit the limit, because audio output will start breaking up. Simply close other apps if this happens. As of Genome 1.0.3, there is now the option of changing the audio latency in Genome. Use a lower latency if you want to have better timing when recording MIDI from other apps or a higher latency if you want to run more apps together.
Future iPad/iPhone hardware should be able to handle more apps running together at the same time. At the time of writing this, the iPad 3 is rumored to feature a quad core processor. This would be a great development for running multiple music apps.