2 Chronicles 5:12

Also the Levites which were the singers, all of them of Asaph, of Heman, of Jeduthun, with their sons and their brethren, being arrayed in white linen, having cymbals and psalteries and harps, stood at the east end of the altar, and with them an hundred and twenty priests sounding with trumpets:)

The Levites which were the singers. On great and solemn occasions, such as this, a full choir was required, and their station was taken with scrupulous regard to their official parts: the family of Heman occupied the central place, the family of Asaph stood on his right, and that of Jeduthun on his left; the place allotted to the vocal department being a space between the court of Israel and the altar in the east end of the priests' court.

With them an hundred and twenty priests sounding with trumpets. The trumpet was always used by the priests, and in the divine service it was specially employed in calling the people together during the holy solemnities, and in drawing attention to new and successive parts of the ritual. The number of trumpets used in the divine service could not be less than two (Numbers 10:2), and their greatest number never exceeded the precedent set at the dedication of the temple. The station where the priests were sounding with trumpets was apart from that of the other musicians; for while the Levite singers occupied an orchestra east of the altar, the priests stood at the marble table on the southwest of the altar. There both of them stood with their faces to the altar. The manner of blowing the trumpets was, first, by a long plain blast, then by one with breakings and quaverings, and then by a long plain blast again (Brown's 'Jewish Antiquities').