The Dark Side of the Moon, released in 1973, was Pink Floyd's eighth studio album and grew into one of the best-selling albums of all time. The record is conceived as a continuous whole around themes of time, money, conflict, mortality and mental strain. Well-known tracks include "Time", "Money", "Us and Them", "Breathe" and "The Great Gig in the Sky", sung by Clare Torry. The band combined blues rock with synthesizers, tape effects and spoken fragments into a cohesive listening experience. Sound engineer Alan Parsons contributed to the record's celebrated sound. The album stayed in the charts for years and is regarded as a milestone in rock history.