Psalms 147:7 - Coke's Commentary on the Holy Bible

Sing unto the Lord with thanksgiving— Hebrew, Answer to the Lord in praise. "Sing alternately;" which may fairly be supposed to be the sense intended by the prophet, as it was the ancient practice to sing alternately. The precentor beginning with the voice, it was usual for the instruments to follow to the same tune and key. See Fenwick, and particularly Bishop Lowth's 19th Prelection.