A Laboratory System for Measuring Loudness Loss of Telephone Connections

A basic Bell System objective--to provide our customers with the best possible telephone message transmission consistent with the 2663 2664 T H E BELL SYSTEM TECHNICAL J O U R N A L , OCTOBER 1971 state of the art and the economic climate--has remained essentially unchanged since the early days of telephony. However, continuing review of the telephone system in terms of this objective has resulted in steady improvement in transmission performance of the system over the years. Such improvement has been made possible by growth in our technical skills; it has been made necessary by evolving customer needs for improved transmission. Indeed, it has been postulated that as our customers use the telephone, they become accustomed to current performance and come to expect further improvement. 1,2 What do we mean by telephone message transmission performance? In the broadest sense, this refers to the effect of the system on speech signals when these signals are transmitted over telephone connections. Customers conversing over telephone connections want to hear reasonably faithful, undistorted reproductions of each others' voices with a minimum of effort. Connections for which these conditions pertain can be thought of as providing satisfactory transmission performance. Connections exhibiting severe distortion would thus provide something less than satisfactory performance; customers might be able to converse but only with extreme difficulty. Speech transmission capabilities of the telephone network are often considered in terms of individual transmission parameters, the combination of which determines overall transmission performance.