John Gill Commentary Numbers 10:5

"And when ye blow an alarm, the camps that lie on the east side shall take their journey." — Numbers 10:5 (ASV)

When you blow an alarm
Making a broken, uneven, and quavering sound, which is called a "tara-tan-tara":

then the camps that lie on the east parts shall go forward ;
the camps of Judah, Issachar, and Zebulun, which lay to the east of the tabernacle, at the front of it; see (Numbers 1:3Numbers 1:5Numbers 1:7) ; this was to be the token for their march, which was first of all; (Numbers 10:14) .