Numbers 10:2-8

2“Make two trumpets of hammered silver to be used for calling the congregation and for having the camps set out. 3When both are sounded, the whole congregation is to assemble before you at the entrance to the Tent of Meeting. 4But if only one is sounded, then the leaders, the heads of the clans of Israel, are to gather before you.

5When you sound short blasts, the camps that lie on the east side are to set out. 6When you sound the short blasts a second time, the camps that lie on the south side are to set out. The blasts are to signal them to set out. 7To convene the assembly, you are to sound long blasts, not short ones. 8The sons of Aaron, the priests, are to sound the trumpets. This shall be a permanent statute for you and the generations to come.