Research Items

Abstract

ELECTRICAL REPRODUCTION OF SPEECH.—The production of sound pictures has made it necessary for research engineers to study very closely the fundamental principles of speech, hearing, and music. In the United States there is now a Society of Motion Picture Engineers, and some of the papers read before it are reproduced in the Bell Laboratories Record for November. Such problems as sound recording, wax recording, recording with the light valve, speed control, sound projector systems, and the fundamental principles of speech, hearing, and music are discussed in an able and interesting way. Studies on the wave forms of speech sounds have shown that the pitch of a man's voice is of the order of 128 cycles per second, whilst that of a woman is of the order of 256 cycles. In both cases overtones occur. Woman's speech is more difficult to interpret than man's. This may be partly due to the fact that it does not disturb the membrane of hearing in so many places. The more difficult consonant sounds in woman's speech are not only fainter, but also require a higher frequency range for interpretation. When by electrical methods frequencies below 100, 200, … 1000 cycles are progressively eliminated from speech, its character changes in a marked way. Timbre or ‘tone colour’ best describes the characteristic lost. For the correct interpretation of speech sounds, frequencies below 300 cycles do not appear to be necessary. When frequencies above 8000, 7000, … 3000 cycles are progressively eliminated, the character of the speech again changes markedly. The characteristic lost may be described as sibilance. It refers to the hissing or frictional character of speech. The impairment produced by eliminating higher frequencies is generally greater in the case of female voices. Timbre seems to be more important in music than in speech. In order to distinguish the tones of various instruments, the fundamental and the first three or four overtones are essential.