We knew you could make great music on the iPhone. With instrument apps such as Smule's Ocarina and Leaf Trombone. Still, while they're cool and surprisingly rich mobile instruments, they're not all that practical for creating, sampling, and recording musical compositions on the fly.
DopplerPad [iTunes Link] is a turntable-like instrument iPhone app built by one of the two creators of FourTrack [iTunes Link]. Unlike some other apps, this one doesn't feature just one instrument - it has 37. It doesn't just play notes; it lets you sample them, no matter where you are. And most of all, you can record and combine the beats to create your own electronic remix.
Want to make a techno beat?
DopplerPad takes some getting used to, but once you get the hang of its interface, there's actually a lot you can do. It uses touch-based responses in order to create an instrumental piece. The 37 instruments we mentioned earlier are almost all techno or electronic-based beats: FM Bass, Cymbals, and even "Space Oddity" are available. You can fine tune the tone of the instruments as well.
Once you're ready, the key to it is picking a beat count, a tempo, and recording your music. You're only allowed up to 16 beats, which is a little disappointing but more than enough to get the job done (and considering you can record more pieces, you can just combine them all later).
Each time you touch the screen while recording, DopplerPad remembers it and plays it back the next time around. This allows you to add instrument after instrument. The DopplarPad video above gives you a good idea, although we want to note that it will take a lot of work before you can make music like they do on the video.