Tiberius and Caius Gracchus

Wherefore, to guard against such digressions, he employed an intelligent servant, Licinius, who stood behind him when he was speaking, with a sounding instrument for giving the tones of the voice their pitch. Whenever this servant noticed that the voice of Caius was getting harsh and broken with anger, he would give out a soft key-note, on hearing which Caius would at once remit the vehemence of his passion and of his speech, grow gentle, and show himself easy to recall.