Tests have been conducted at Bell Laboratories within the last 10 years to obtain subjective evaluations of the effects of loss, noise, and talker echo on telephone transmission quality. We use these subjective test results to formulate graphical and analytical models of subjective opinion that can be used in network planning studies to evaluate transmission performance of the network and to study the effects of network changes on performance. These models are based on the concept of a generalized transmission‐rating scale. Separate opinion curves for each test take into account differences caused by factors such as subject group, type of test, and range of conditions. We also describe the methods of data analysis used in the formulation of the transmission‐rating scale and opinion models, provide a comparison of the test results with the models, and discuss the models in sufficient detail to permit their application in transmission planning studies.

No abstract

Any appreciable listener echo on telephone lines is perceived as undesirable, and considerable effort is expended to hold echo to acceptable levels. To provide a basis for appropriately controlling listener echo, a series of four subjective tests was conducted at Bell Laboratories to obtain subjective evaluations of the effects of listener echo on telephone transmission quality. The subjective tests included conditions in which the listener echo‐path loss was flat or frequency‐shaped by selective filtering. The test results showed that subjective opinions for conditions with the same singing margin (minimum value of echo‐path loss) were highly dependent on the frequency shaping. A weighted echo‐path loss (wepl) is defined to provide a weighting on the frequency‐shaped test conditions so that subjectively equivalent test conditions have approximately the same levels of wepl. The results of these subjective tests are used to formulate a model of subjective opinion for use in network planning studies. The resulting listener echo opinion model is incorporated into an existing transmission rating model which encompasses loss, noise, and talker echo. Objectives are proposed for listener echo based on wepl.

No abstract

The operation and maintenance of the TH and TD-2 radio relay systems require communication facilities along the route which can be used for the transmission of voice, protection switching and alarm signals. Special narrow-band microwave facilities, referred to as the auxiliary radio channels, which have been developed as an integral part of the TH system to supply this need, are described in this paper.