We're used to disappointing people when it comes to talking about Android and music making but, in this case, there is some good news.
Although there are more dedicated Ableton Live controller apps available for iOS (the likes of touchAble, LiveControl 2 and Conductr), one of them, namely the LK - Live Controller, does work with Android as well.
The app itself is free, but you can customise its features via in-app purchasing of different modules. These enable you to launch clips, play on MPC-style pads, work with virtual knobs and faders, tweak an X/Y pad and more.
A touch of class
Another option is Hexler's TouchOSC, a modular OSC and MIDI controller app that works over Wi-Fi. This actually enables you to control any OSC/MIDI-compatible software - there's a bit of setting up involved and a learning curve to deal with but, if you're serious about turning your Android device into a controller, it's well worth the £3.99 admission fee.
Finally - and this is certainly a more obscure suggestion - we've also heard about a system from Hollyhook called midiHook, which actually enables you to translate data generated by your Android device's sensors (accelerometer, gravity and linear acceleration for example) into MIDI data. It's not strictly a controller app, but you might have some fun tinkering with it, and the beta release is free.
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