C. F. Keil and Franz Delitzsch on 2 Chronicles 29:26-27

2Ch 29:26-27 דויד כּלי are the musical instruments the use of which David introduced into the public worship; see 1Ch 23:5. - The first clause, 2Ch 29:27, “And Hezekiah commanded to offer the burnt-offering upon the altar,” is repeated from 2Ch 29:21 to form a connection for what follows: “At the time when the sacrificial act began, the song of Jahve commenced,” i.e., the praising of Jahve by song and instrumental music (יהוה שׁיר = ליהוה שׁיר,   1Ch 25:7), and (the blowing) of trumpets, “and that under the leading (ידי על) of the instruments of David.” This is to be understood as denoting that the blowing of the trumpets regulated itself by the playing of the stringed instruments-suited itself to the song and the music of the stringed instruments.