Numbers 10:3-8

³When both trumpets are blown, all the Israelites are to gather before you at the entrance to the Tent of Meeting.

⁴But if only one is blown, then only the tribal leaders are to gather before you.

⁵When you blow the trumpet loudly, which is the alarm signal to move out, the camps on the east side are to march out first.

⁶When you blow the trumpet loudly the second time, the camps on the south side are to march out. That's their signal to start moving.

⁷To summon the people, blow the trumpets normally, not the loud alarm signal.

⁸Aaron's descendants are to blow the trumpets. This regulation is for all time and for all future generations.