IEEE 661-1978 pdf free.IEEE Standard Method for Determining Objective Loudness Ratings of Telephone Connections.
The methods that are used to measure the transmission performance of telephone connections may be divided into twoclasses: objective methods and subjective methods. This standard considers an objective method that can be used formeasuring telephone connections in a manner that reflects the subjective attribute of loudness with an accuracysuitable for most telephone transmission engineering problems. The performance measure is expressed in terms of adefined reference and is referred to as an objective loudness rating.
The objective method utilizes a sound source to activate the telephone transmitter, and an acoustic coupler andassociated microphone (artificial ear) as an acoustic termination for the telephone receiver. The sound source consistsof a source of electric energy, a special type of loudspeaker unit(artificial mouth), and such supplementary electric andacoustic components as may be required so that the ensemble provides a controlled sound field.
The artificial mouth and artificial ear provide a simpler means of measuring characteristics of telephone connectionsthan is possible with the human mouth and ear. The practical design of artificial mouths and artificial ears is such thatthey only approximate their respective human counterparts.Thus telephone connection characteristics measured usingthese devices will only approximate and not duplicate those characteristics measured with human mouths and ears.However, experience has shown that characteristics determined using these devices are highly useful in telephonetransmission engineering.
Subjective methods for rating the transmission performance of telephone connections involve human talkers andlisteners. Commonly used subjective test methods include those based on loudness assessment, articulation, andjudgment. [1-4].’ The particular method employed in any given situation depends on the transmission parameter(s) tobe evaluated and on the performance measure criterion of interest, for example, articulation or loudness.
Subjective methods have the particular advantage that ratings obtained are direct measures of performance.A majordisadvantage of subjective methods is that they often require large groups of human subjects for long time periods inorder that the results have significance. Objective methods,on the other hand, involve somewhat simpler and bettercontrolled measurements, and a large number of measurements can be made in a relatively short period of time.Moreover, measurements can be obtained that reflect subjective evaluation with suitable accuracy.
This standard is concerned with a specific objective method of determining the loudness ratings of telephoneconnections. The method is based on objective measurements and computations performed in such a manner that thenumerical results obtained reflect the subjective attribute of loudness.IEEE 661 pdf download.