IEEE 661-1997 pdf download IEEE Standard Method for Determining Objective L oudness Ratings of Telephone Connections
2. Scope and Purpose
2.1 The purpose of this standard is to describea practical and reproducible method of determining the loudness ratings of telephone connections. Loudness rating may be measureddirectly using appropriate test instruments andfacilitiesas specified in this standard,or maybe computed using the amplitude-frequencycharacteristic of the connection measured inaccordance with IEEE Std 269-1971[5].2.2 Loudness ratings determined using thisstandard may not exactly duplicate subjectiveloudness evaluations. Moreover,measured ratings and computed ratings determined using thisstandard may not agree, particularly if the connection incorporates nonlinear elements. However, differences are expected to be acceptablysmall for engineering purposes. For exampledifferences for connections utilizing linearmicrophones are expected to be small,result.ing only from instrument and measurementerror, while for connections employing nonlinear microphones,for example,carbon microphones, the differences may be larger.
NOTE: For the purposes of this standard, a linear micro-phone is one that exhibits a one-to-one relation betweeninput pressure and output yoltage over its norral operating ran议劈ge.
23 The procedures given in this standard maybe used for determining the loudness rating ofpartial and complete telephone connectionsFor complete telephone connections,comprising overall and sidetone transmission paths, theprocedures involve measurement of acousticinput and output pressures.
For partial telephone connections comprisingtransmitting, receiving, or connection paths the procedures involve measurement of acoustic pressures and electric voltages.
2.4 Transmission planning of switched tele.phone networks is generally accomplished byworking with parts of connections, for example.customer loops (telephone sets,line facilities.and feeding bridges) or trunks, to ensure thatwhen these parts are switched together, the re-sulting overall connections perform satisfactorily. When planning is based on loudness,thesum of the loudness losses determined for partsof a connection should closely approximate theloudness loss of the overall connection. Forsuch purposes the recommended analysis bandwidth is 300-3300 Hz,which approximates thebandwidth of the more band-limiting components typically found in modern telephone networks. There may be cases in which a widerbandwidth would be desirable (see Appendix A)and the methods of this standard will accom-modate such wider bandwidths.
2.5 The method of this standard is based onspecification of (1) characteristics of a suitableartificial mouth，(2) a standard artificial earand (3) appropriate auxiliary measuring instru.ments and facilities. The method is intendedfor rating connections involving telephone setsequipped with handsets. The applicability ofthe method for the measurement of telephonesets incorporating special devices such as noiseexclusion transmitters,distant-talking transmitters,ear insert receivers, or noise-exclusion receivers (receivers equipped with circumauralearpads) has not been reviewed.However,theloudness theory on which this standard is basedis sufficiently general that advances in the artmay permit measurement of many such specialdevices using the methods specified in thisstandard.
IEEE 661-1997 pdf download
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