A System of Effective Transmission Data for Rating Telephone Circuits

in service. Laboratory talking tests, such as articulation tests, indicate the ability of the circuit to transmit speech sounds under the conditions of the tests. In service, however, a wide and complex range of conditions is encountered and in the case of a new kind of instrument or circuit the service conditions may be modified in an unpredictable way due to the users' reactions. The complexity and a priori uncertainty of these conditions point to the advantage of ratings obtained during actual service. The real criterion for rating a circuit is its transmission performance when in actual use as a link in the extremely complicated and variable communication channel between the brain of one telephone user and the brain of another telephone user. The paper by Mr. Martin fully developed this idea and described a quantitative method for providing ratings on this basis of the transmission performance of a circuit, which method includes the effects of such circuit characteristics as volume loss, noise, distortion and sidetone. This method uses as a measure of circuit performance the number of repetitions requested by normal telephone users per unit time while using the circuits in actual service, on the basis that this number is a direct quantitative measure of the success with which telephone users carry on conversations. The previous paper also discussed other methods of rating the transmission performance of telephone circuits such as articulation 1 1 2