iPad Demo -> http://www.youtube.com/watch?v=uD9W1Cv0Ies
Intuitive synthesizer using four multitouch points on the screen and the accelerometer to give a large amount of control over a sine wave output.
Controls
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Orange - Volume and Pitch (radius controls pitch range).
Pink - Ramp speed and note length,
Blue - Delay Length and Pitch - hold down to activate delay.
Green - Delay Filter and Feedback - only active when blue dot is held.
Accelerometer controls pitch and wave shape.