Parashas Behar · Aliyah 1 · Passuk 25:09
Chabad.org — English translation + Rashi
Torah Temimah cites Rosh Hashanah 34a.
English: “And you shall sound a shofar.” It is said here “and you shall sound a shofar” and it is said there “and Moshe commanded and they caused a voice to pass through the camp”: just as there [it is] with a voice, so here with a voice.
Gezeira shavah (Bavli Rosh Hashanah).
The shofar blast of Yovel must be an audible voice/sound, derived by Gezeira shavah from the “passing of a voice” in the camp.