A first transmitter transmits a first propagating signal to a receiver through a first region of a touch input medium corresponding. A second transmitter transmits a second propagating signal to the receiver through a second region where the second region is a subset of the first region. At least the first propagating signal and the second propagating signal are analyzed to identify, based on a determination that the first signal path was disturbed by a touch input while the second signal path was not disturbed by the touch input, the touch input on a part of the first region that is not part of the second region.