Precedent: ‘A touchless 3d tracking interface’ by steve hobley on makezine

(https://makezine.com/projects/a-touchless-3d-tracking-interface/) shows a simple way of using basic components to construct a capacitive sensing circuit, the application is a 3d interface which could be visualized in processing.

As shown in the video, the changing signal can be read by arduino when moving the hand towards the plates. The similar circuite can be used in touch-sound applications. Steve's circuite is shown below.

He also suggested that the 220k resistor can be changed to a 500k potentiometer to manual adjust sensitivity.