A computerized musical percussion instrument is disclosed.Markers carried by the musician are observed by an imager to produce a series of two dimensional images over the time of the performance.A processor receives the images and distinguishes between markers (e.g. left hand, right hand) by comparing the position and size of unidentified markers in the current image to the position and size of identified markers in preceding images.The processor analyzes each markers' movements and detects a drum hit when a marker undergoes a sharp reversal of its motion direction after reaching sufficient speed. The processor determines which drum the musician intends to hit by comparing the position and size of the marker at the instant of the hit to the position and size attributes of each drum. The processor outputs an audio signal for each hit, corresponding to the drum hit, with a volume determined by marker speed.