Here is a musicologist who is also a student of the Scriptures. Thus he is able to follow and produce musical notes embedded in psalms and prayers found in the Bible.
This, he says, is the prayer, Shema Israel (“Hear, O Israel: the Lord Our God Is One”), played on the harp according to the same notes David would have used.
This is what Saul heard, when David played to calm the king’s spirit.