Indicial Response of Telephone Receivers

T HE use of indicial response analysis as an outgrowth of the Heaviside operational calculus 1 has been extended to a number of different fields. The indicial admittance as defined by J. R. Carson 2 in his analysis of the submarine cable and other transmission problems has been an effective tool in the study of transients. More recently, a similar type of measurement has been used as an indication of performance of amplifiers 3 , television equip-* ment 4 , and audio frequency transformers 5 . In the field of telephone receivers 6 an analysis by means of impressed square waves has been found useful as a measure of transient response. In the transmission of speech, so much emphasis has been placed upon steadystate frequency response as an indication of performance, that it seems in order to consider the possible advantages of a transient method of analysis, as obtained by measuring the indicial response. Only recently has the technique of such measurement been made feasible by the improvement at low frequencies of amplifiers and related apparatus. T H E INDICIAL RESPONSE