This app its so good that I've downloaded in my android mobile it is useful and the sound is produced by stricking the bars with mallets. The mallets are held with the palm facing downward. The low notes require a stronger attack to set the larger bars vibrating. The chromatic orchestra marimba consists of two parallel rows of bars. It can also change to xylophone can be used in a variety of musical genres. And vibraphone that has tuned metal bars and is simular in shape to a xylophone.