Matthew Poole and continuators on Psalms 81:3

3 Blow up the trumpet in the new moon , in the time appointed, on our solemn Feast-day ▪

Which was a sacred and festival time, as appears from Numb. 10. 10. and 28. 11, 14. 2 Kings 4. 23. Isa. 66. 23 But this may be understood either 1. Generally of every New Moon. Or rather, 2. Specially of that New Moon, as the word may be rendred, which begun the seventh month; as may be gathered both from the following words, and by comparing this place with Levit. 23. 24. and Numb. 29. 1. Where this very day is called a day of blowing of Trumpets.

Or, for the day, or time of our solemn festivity; whereby may be understood either 1. the day of the New Moon, on which the Trumpets were blown for the celebration of that solemn time. Or 2. The seventh Month, which that New Moon did introduce or begin, and in which, besides other Solemnities, they kept the Feast of Tabernacles, which the Hebrew Doctours call the Feast by way of eminency, and Iosephus affirms to have been the most sacred and the chief of all the Jewish Feasts.