Today's Morning Edition music is from Mother Father Sister Brother featuring vocals by The Three Degrees with the song "The Sound of Philadelphia." It was number one on the pop charts 40 years ago today. Mother Father Sister Brother was a group of thirty studio musicians based at Philadelphia's Sigma Sound Studios. The mostly-instrumental recording became the theme song for the television program "Soul Train." It is considered by many to be the first disco song to make it to the top of the charts.