Exodus 19:16, 19

So it happened on the third day, when it was morning, that there were thunder and flashes of lightning, and a thick cloud was on the mountain, and a very loud blast was sounded on a ram’s horn, so that all the people who were in the camp trembled.

And it happened, as the blast of the ram’s horn grew louder and louder, Moses spoke and God answered him with [a voice of] thunder. [Deut 4:12]