Philadelphia Voices is the eighth in a series of “crowd-sourced symphonies” – symphonic scores incorporating sounds recorded on the streets and submitted by residents – Machover has done for various cities from Detroit to Toronto to Perth. David Patrick Stearns met with the composer, both in Philadelphia and at his high-tech Boston-area studio, to talk about how Machover put together the piece, which will combine the sounds of the Philadelphia Orchestra and several choirs with such found sounds as Mummers at the New Year’s Day parade, birds at the Philadelphia Zoo, and (yes) sizzling cheesesteaks on the grill at Pat’s King of Steaks in South Philly.