IEEE 269-1983

The purpose of this standard is to describe a practical method for measuring the transmission characteristics of a telephone set by means of objective measurements on a test connection. The test results thus obtained may be used as a means of evaluating or specifying the transmission performance of a telephone set on a standardized basis. The basic accuracy and reproducibility of measurements made in accordance with this standard will depend primarily upon the accuracy of the test equipment used, the care with which the measurements are conducted, and the inherent stability of the telephone set or transducers under test, or both. Where a given set of measurements is repeated in the same laboratory and by the same operator, a relatively high degree of reproducibility should normally be obtained. However, when comparing measurements made by different laboratories, allowances should be made for the influencing factors mentioned above.

Revision Standard - Superseded. The methods that are used to measure telephone-set transmission performance may be divided into two classes: objective methods and subjective methods. The objective methods, which are those discussed in this standard, utilize a sound source resembling the human mouth to drive the transmitter, and an acoustic coupler resembling the human ear as a termination for the receiver. The sound source comprises a source of electrical energy and a moving-coil loudspeaker unit having supplementary electrical and acoustical components which produce a sound field simulating that of a typical human voice. This special loudspeaker is referred to as an artificial mouth. The acoustic coupler comprises a microphone and a terminating air volume having supplementary acoustic components which produce a load on the receiver simulating that of a typical human ear. This coupler is referred to as an artificial ear. The artificial mouth and ear are useful in comparing the performance of telephone sets at frequencies in the significant portion of the speech range.