A Voice and Ear for Telephone Measurements

HE performance of telephone transmitters and receivers is dependent not only upon their physical characteristics but also upon the reactions of the users to these instruments. Observations of the results obtained by subscribers under known conditions of practical telephone use take both these factors into consideration. Tests of this kind, however, are not suited to the needs of laboratory development and study of instruments where data regarding their physical characteristics are required. In such instances data, to be of greatest value, should be taken under conditions which include those factors of actual service having an important bearing on the performance of the instruments. Among the most important of such factors are the voice and ear. For making many of the laboratory tests, therefore, it has been necessary to employ actual human voices and ears in order to insure that all of their physical characteristics have been included in the test. This procedure, however, due to uncontrollable variations in individuals, requires a large expenditure of time and effort to insure the precision desired. Furthermore, certain instrument tests, such as response-frequency characteristics, are either impossible or difficult to make with the real voice or ear. These disadvantages, inherent in the use of the human voice and ear, have been recognized for a long time. Numerous attempts have been made to employ voice and ear substitutes for instrument testing, and in cases where uniformity of instruments rather than their design has been of primary importance, as in shop acceptance tests, such substitutes have been of great value.