Exodus 19:19

הולך וחזק מאד WAXED LOUDER AND LOUDER — The manner of an ordinary person is that the longer he continues to blow a trumpet the sound he produces becomes weaker and fainter; but in this instance it went on getting stronger. And why was it thus (i. e. not so loud) at first? To make their ears receptive to as much as they were able to hear (Mekhilta). משה ידבר MOSES SPAKE — When Moses was speaking and proclaiming the Commandments to Israel — for they heard from the Almighty’s mouth only the Commandments אנכי and לא יהיה לך, whilst the others were promulgated by Moses — then the Holy One, blessed be He, assisted him by giving him strength so that his voice might be powerful and so become audible (Mekhilta). יעננו בקול signifies He answered him in respect to (ב) the voice, just as (1 Kings 18:24) “He that answereth באש” — “in respect to the fire” — i. e. by causing fire to descend. (So here: God answered Moses’ petition that his voice might become audible to the vast concourse of people).

וַֽיְהִי֙ ק֣וֹל הַשֹּׁפָ֔ר הוֹלֵ֖ךְ וְחָזֵ֣ק מְאֹ֑ד מֹשֶׁ֣ה יְדַבֵּ֔ר וְהָאֱלֹהִ֖ים יַעֲנֶ֥נּוּ בְקֽוֹל׃

And then the voice of the shofar sounded louder and louder; Moshe speaks, and God answers him by a voice.