Ambient music is a genre of music that emphasizes tone and atmosphere over traditional musical structure or rhythm. A form of instrumental music, it may lack net composition, beat, or structured melody. It uses textural layers of sound which can reward both passive and active listening and encourage a sense of calm or contemplation. The genre is said to evoke an "atmospheric", "visual", or "unobtrusive" quality. Nature soundscapes may be included, and the sounds of acoustic instruments such as the piano, strings and flute may be emulated through a synthesizer.