New Defender's Study Bible Notes
15:19 Heman, Asaph, and Ethan. These three musicians are probably the same men whose names appear in the superscripts of some of the psalms—Heman (see Psalm 88), Asaph (Psalms 50, 78-83), and Ethan (Psalm 89).
15:21 harps on the Sheminith. It has been suggested that the “Sheminith” refers to the musical scales.