Discussion on “effect of iron in distorting alternating-current wave-form”, at Pittsburg Branch, October 9, 1906

S. P. Grace: The sounds of the human voice are not by any means pure tones. In a single sound will be found what we may call the fundamental tone or that of the lowest frequency and, in addition, the harmonics produced by the partial vibration of the vocal chords and the resonating air of the throat and mouth. In telephone transmission the frequencies which are important have a wide range. The lowest are those of the low voice, probably none below 100 periods per second, and ranging upward to 1500 periods per second.