Upon an instrument of ten strings,.... An harp of ten strings, as the Targum. The harp invented by Terpander had only seven strings c; according to Pliny d; Simonides added the eighth, and Timotheus the ninth; but this of David was of ten strings:
and upon the psaltery; of which Psalms 33:2, "upon the harp with a solemn sound"; or "upon higgaon with the harp"; which "higgaon", Aben Ezra says, was either the tune of a song, or an instrument of music; all these instruments of music were typical of the spiritual joy and melody which the saints have in their hearts when they praise the Lord; hence mention is made of harps in particular in this spiritual sense, under the Gospel dispensation, Revelation 5:8.
c Suidas in voce τερπανδρος. Plin. Nat. Hist. l. 7. c. 56. d Ibid.