laptop plays ultrasonic tone · phone blocks it · shadow depth → audible drone · shadow void visualizer · no phone app · runs locally
sound travels in straight lines. your phone doesn't.
move it between the speaker and microphone. the shadow it casts in sound is the instrument.
laptop plays a 18.5khz ultrasonic tone · mic measures received amplitude · shadow = baseline − received · shadow depth drives drone pitch + volume · no phone software required