Punk rock and hip-hop. Disco and salsa. The loft jazz scene and the downtown composers known as Minimalists. In the mid-1970s, New York City was a laboratory where all the major styles of modern music were reinvented-all at once, from one block to the next, by musicians who knew, admired, and borrowed from one another. Crime was everywhere, the government was broke, and the city's infrastructure was collapsing. But rent was cheap, and the possibilities...