In this case, the "old southern sound" is the term Bill Monroe used to describe his music. Even though his music is now considered innovative and created a music genre, I believe he felt that it was based on the old sounds that echoed through the Appalachians, the same sounds he grew up with and shaped his musical identity.

The old southern sounds were the ones that he was trying to capture, the old ballad, an old minstrel song or blues song that fertilized the hills of his youth. Monroe probably though of himself as a preserver not an innovator. I don't think he was really aware of his destiny but he was stubborn and stuck to his music. And for that he should be admired.

-Richie