1) The hidden musical gem of the Three Rivers Arts Festival might be L.P. a crystal-voiced, singer-songwriter from L.A. Her sound features a power pop/rock band with great guitars, drums and vocals. One of her songs is interestingly titled, “Suburban Sprawl & Alcohol.” L.P. has written and co-written songs for Pittsburgh native Christina Aguilera, Rihanna and the Backstreet Boys. Show starts at 8:10…