Speech Signal Power in the Switched Message Network

A methodology for evaluating the intelligible crosstalk performance of voice‐frequency customer loops is developed in this paper. Using this methodology, intelligible crosstalk probabilities are calculated for a representative sample of loops in the plant. The effect of gain on loop crosstalk performance is then evaluated for a particular example of gain application where length‐dependent gain ranging approximately from — 1 to 9 dB is added. Two possible locations of gain application are evaluated: the central office and the telephone set. Presently, no crosstalk performance objectives exist for loops. For planning purposes, however, an intelligible crosstalk probability of 0.1 percent has been used in the past as a limit for satisfactory performance. In comparison with this limit, the crosstalk performance of the present loop plant (loops without gain) is satisfactory. For the particular example of gain application considered in this paper, gain applied at the central office has only a small effect on loop crosstalk performance. However, gain applied at the telephone set degrades loop crosstalk performance significantly, increasing the crosstalk probability above the 0.1 percent level on about 15 percent of the sample loops evaluated.

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A Model for the Subjective Effects of Listener Echo on Telephone Connections

Cavanaugh¹,

Hatch²,

Neigh³

1980

Bell System Technical Journal

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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.

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Speech Signal Power in the Switched Message Network

Cited by 12 publications

References 5 publications

Phase Shift Keying (Psk) Modulation, Demodulation, and Performance

Phase Shift Keying (Psk) Modulation, Demodulation, and Performance

Intelligible Crosstalk Performance of Voice-Frequency Customer Loops

A Model for the Subjective Effects of Listener Echo on Telephone Connections

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