An impressive group of fiddlers from around the country is gathering this week to teach at Boston’s Berklee College of Music for the Mark O’Connor Summer String Program. They represent a wide array of styles, including bluegrass, jazz, Irish, classical, Scottish, blues, hip hop, Texas swing, and more. Best of all, the stellar faculty are performing in a showcase concert Friday night at the Berklee Performance Center. Whether you are a fan of string music or an aspiring musician, this show promises to be full of virtuosity, authenticity, authenticity, and heart.