Charles H. Spurgeon on Psalms 81:3

"In the new moon, "etc. The feast of the new moon was always proclaimed by sound of trumpet. For want of astronomical knowledge, the poor Jews were put to sad shifts to know the real time of the new moon. They generally sent persons to the top of some hill or mountain about the time which, according to their supputations, the new moon should appear. The first who saw it was to give immediate notice to the Sanhedrim; they closely examined the reporter as to his credibility, and whether his information agreed with their calculations. If all was found satisfactory, the president proclaimed the new moon by shouting out, wdqm mikkodesh! "It is consecrated." This word was repeated twice aloud by the people; and was then proclaimed everywhere by blowing of horns, or what is called the sound of trumpets. Among the Hindus some feasts are announced by the sound of the conch, or sacred shell. Adam Clarke.