Steelpan is musical instruments called a steel drum. It was developed in island nation Trinidad & Tobago in Caribbean Sea.
Musical instruments named Mini Steelpan only of 11 music scales that was able to be performed easily were put in iPhone/iPod Touch.
To do the tremolo, long touch some note or two different notes.
Photo by 民族楽器コイズミ in Japan.
http://www.koizumigakki.com/