1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 0 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%0(/.%G0G042!.3-)33)/.G0G015!,)49-%!352%-%.43G0G02%,!4%$G0G04/G0G030%#(,/5$.%33$%4%2-).!4)/.G0G0/ FUNDAMENTAL PRINCIPLES(Geneva, 1976; amended at Geneva, 1980Malaga-Torremolinos, 1984, Melbourne, 1988)Pref
2、aceThis Recommendation is one of a set of closely related Recommendations concerned with determination ofloudness ratings. The present one deals with the fundamental principles and the others, as follows, deal with certainadditional matters1).Recommendation P.48 Specification for an intermediate ref
3、erence systemRecommendation P.78 Subjective testing method for determination of loudness ratings in accordance with Recommendation P.76Recommendation P.64 Determination of sensitivity/frequency characteristics of local telephone systems to permit calculation of their loudness ratingsRecommendation P
4、.79 Calculation of loudness ratingsRecommendation P.65 Objective instrumentation for the determination of loudness ratings1 IntroductionA speech path is, broadly, a transmission path that exists between a talkers mouth and the ear of a listener or, inthe case of sidetone, between the mouth and ear o
5、f a talker. In typical face-to-face conversation, the speech istransmitted by means of the air path connecting the mouth and ear. Depending on environmental conditions,transmission may be:a) more or less direct, as in the case of two persons conversing in an open, unobstructed location, such as agol
6、f course;b) largely indirect, as in the case of two persons conversing in a small, hard surfaced room where a largeproportion of the energy reaching the ear may be due to reflections from the walls, ceilings and floor; orc) something between the two extremes of a) and b).In the case of telephony, th
7、e air path is replaced by a system comprising:a) an air path from the mouth to the telephone microphone;b) an air path between the telephone earphone and the ear; andc) a telephone connection consisting of the microphone, earphone and interconnecting circuitry together witha similar system for the r
8、everse direction of transmission. The two situations - face-to-face and using thetelephone - differ appreciably in detail but, for speech transmission purposes, they are alike insofar as theirfunction is to provide a means of both-way speech communication.Telephone engineering is concerned with prov
9、iding telephone connections which, while not identical to theface-to-face situation, are comparable in effectiveness for providing a means of exchanging information by speech;such telephone connections should also optimize customer satisfaction within technical and economic constraints.Various tools
10、 are used by transmission engineers in planning, design and assessment of the performance oftelephone networks. Reference equivalent, based on the criterion of loudness of speech emitted by the talker andperceived by the listener, has been one of the most important of these tools; it provides a meas
11、ure of the transmissionloss, from mouth to ear, of a speech path._1)The present Recommendation together with Recommendations P.48, P.78 and P.79 provide complete definitions of overall,sending, receiving and junction loudness ratings, and Administrations are invited to use them to further their stud
12、ies of Question19/XII 1.2 Volume V - Rec. P.76The reference equivalent method is defined in Recommendations P.42 and P.72 Red Book and its fundamentalprinciples are briefly explained in 2. The method for determining loudness ratings of local telephone circuits is basedupon rather similar fundamental
13、 principles but comprises modifications which render it much more flexible and shouldgreatly simplify transmission planning.A desire to depart from use of reference equivalents as defined by Recommendation P.72 Red Book arises fromthe following reasons:1) reference equivalents cannot be added algebr
14、aically; discrepancies of at least 3 dB are found;2) replication accuracy of reference equivalents is not good; changes in crew can cause changes of as much as5 dB;3) increments of real (distortionless) transmission loss are not reflected by equal increments of referenceequivalent; 10 dB increase in
15、 loss results in an increase in reference equivalent of only about 8 dB.Use of loudness ratings defined in accordance with the principles given below should largely obviate thesedifficulties.In addition to these advantages, the same values of loudness ratings should be obtained whether thedeterminat
16、ion is by subjective tests, by calculation based on sensitivity/frequency characteristics or by objectiveinstrumentation. The fundamental principles of the method are described below and these differ from those applicableto reference equivalents by the least possible extent to achieve the desirable
17、flexibility.The loudness rating (which has the dimensions and sign of “loss”) is, in principle, like the reference equivalent,defined by the amount of loss inserted in a reference system to secure equality of perceived loudness to that obtainedover the speech path being measured. Practical telephone
18、 connections are composed of several parts connectedtogether. To enable the transmission engineer to deal with these parts in different combinations, loudness ratings mustbe defined in a suitable manner so that “overall”, “sending”, “receiving” and “junction” ratings can be used.“Sidetone” loudness
19、ratings can also be determined in an analogous manner. Sidetone reference equivalent isdefined in Recommendation P.73 Red Book and sidetone loudness ratings are defined in 3 below.2 Definitions of loudness ratings for principal speech paths2.1 General 2 deals with principal speech paths, namely from
20、 a talker at one end of a connection to a listener at the other.Sidetone paths are treated in 3 below.In general, loudness ratings are not expressed directly in terms of actual perceived loudness but are expressedin terms of the amounts of transmission loss, independent of frequency, that must be in
21、troduced into an intermediatereference speech path and the unknown speech path to secure the same loudness of received speech as that defined by afixed setting of NOSFER. This implies that some interface exists or could, by some arrangement, be found in theunknown speech path into which the transmis
22、sion loss can be introduced. In practice the unknown speech path iscomposed of a sending local telephone circuit coupled to a receiving local telephone circuit through a chain of circuitsinterconnecting the two local systems2). Figure 1/P.76 shows this subdivision of one principal speech path of ate
23、lephone connection. The interfaces JS and JR separate the three parts of the connection to which loudness ratings areassigned, namely: sending loudness rating, from the mouth reference point to JS; receiving loudness rating from JR tothe ear reference point; and junction loudness rating from JS to J
24、R. The overall loudness rating is assigned to thewhole speech path from mouth reference point to ear reference point._2)See Annex B for explanation of certain terms.Volume V - Rec. P.76 3Note that in practical telephone connections:a) the transmission loss of the junction may be frequency dependent;
25、b) the image impedances of the “junction” may not be constant with frequency and may not be resistive;c) the impendances of the local telephone systems presented to the junction at JS and JR may not be constantwith frequency and may not be resistive;d) impedance mismatches may be present at JS or JR
26、 or both.Overall loudness ratings (OLRs), sending loudness ratings (SLRs), receiving loudness ratings (RLRs) andjunction loudness ratings (JLRs) are defined so that the following equality is achieved with sufficient accuracy forpractical telephone connections.OLR = SLR + RLR + JLR2.2 Definitions of
27、overall, sending, receiving and junction loudness ratingsFigure 2/P.76 shows the principles used to define the overall, sending, receiving ad junction loudness ratings.2.2.1 Overall loudness ratingPath 1 in Figure 2/P.76 shows the complete unknown speech path subdivided into local telephone systems
28、andjunction. In this example the junction comprises a chain of circuits represented by trunk junctions (JS-NS and NR-JR)and trunk circuits (NS-IS, IS-IR and IR-NR). A suitable arrangement for inserting transmission loss independent offrequency must be provided at some point such as in IS-IR.4 Volume
29、 V - Rec. P.76Path 2 shows the complete intermediate reference system (IRS) with its adjustable, non-reactive, 600 ohmsjunction between JS and JR.The level of received speech sounds to which the additional loss x1in Path 1 and the junction attenuator settingx2of Path 2 are both adjusted is defined b
30、y using the fundamental reference system NOSFER with its attenuator set at25 dB. When these adjustements have been made, the overall loudness rating (OLR) of the complete unknownconnection is given by (x2 x1) dB.2.2.2 Sending loudness ratingPath 3 in Figure 2/P.76 shows the IRS with its sending part
31、 replaced by the local telephone system of theunknown. The junction is adjusted to produce, via Path 3, the same loudness of received speech sounds as theNOSFER with its attenuator set at 25 dB. If x3is the required setting in Path 3, the sending loudness rating (SLR) isgiven by(x2 x3) dB.Volume V -
32、 Rec. P.76 52.2.3 Receiving loudness ratingPath 4 in Figure 2/P.76 shows the IRS with its receiving part replaced by the local telephone system of theunknown.The junction is adjusted to produce via Path 4 the same loudness of received speech sounds as the NOSFERwith its attenuator set at 25 dB. If x
33、4is the required setting in Path 4, the receiving loudness rating (RLR) is given by(x2- x4) dB.2.2.4 Junction loudness ratingPath 5 in Figure 2/P.76 shows the IRS with its junction replaced by the unknown chain of circuits as located inPath 1 of Figure 2/P.76 between JS and JR. The arrangement for i
34、ntroducing transmission loss, independent offrequency, must be provided as was required in Path 1. The additional loss is adjusted to produce, via Path 5, the sameloudness of received speech as the NOSFER with its attenuator set at 25 dB. If x5is the required additional loss inPath 5, the junction l
35、oudness rating is given by (x2 x5) dB.2.3 Conditions under which loudness ratings are determined2.3.1 GeneralThe loudness of received speech sounds depends upon certain factors that are not well defined under practicalconditions of use, but must be defined as precisely as possible to obtain accurate
36、ly reproducible loudness ratings.Clearly, as shown in Figure 1/P.76, the loudness rating is largely governed by the characteristics of the mouth-to-earpath. This path can be made precise by defining a mouth reference point at which the sound pressure pMof speechemitted by the talker is measured or r
37、eferred, and an ear reference point at which to measure or to which to refer thesound pressure pEof speech reproduced by the earphone. These points can be chosen in a fairly arbitrary manner andthis becomes important when loudness ratings are to be determined objectively; suitable definitions for su
38、ch purposesare given in Recommendation P.64 which deals with measurement of sending and receiving sensitivity/frequencycharacteristics.It is essential, however, to define vocal level, speaking distance, microphone position and listening conditionswhich govern the fit of the earphone to the ear. Thes
39、e are indicated in Figure 1/P.76. The essential features that definethe conditions under which loudness ratings are determined are indicated in Table 1/P.76.Some remarks on the items listed in Table 1/P.76 are given below.2.3.2 Intermediate reference systemThe intermediate reference system is define
40、d in Recommendation P.48. It has been chosen with the followingin mind:a) It shall correspond approximately, as far as the shapes of sending and receiving frequency characteristicsare concerned, with those of national sending and receiving systems in use at present and likely to be usedin the near f
41、uture. For this reason the frequency bandwidths for sending and receiving parts are confined tothe nominal range 300-3400 Hz3).b) The absolute sensitivity has been chosen to reduce as much as possible changes in values from referenceequivalents to loudness ratings.c) In external form its handsets ar
42、e similar to conventional handsets used in actual telephone connections._3)The IRS is specified for the range 100-5000 Hz (see Recommendation P.48). The nominal range 300-3400 Hz specified isintended to be consistent with the nominal 4 kHz spacing of FDM systems, and should not be interpreted as res
43、trictingimprovements in transmission quality which might be obtained by extending the transmitted frequency bandwidth.6 Volume V - Rec. P.76TABLE 1/P.76Conditions under which loudness ratings are determinedNo. Item specified Specification1 Intermediate reference system Recommendation P.482 Vocal lev
44、el of speaker As Recommendation P.72(Red Book)3 Level of received speech sounds at which loudness is judged constant NOSFER set at 25 dB4 Handset position relative to talkers mouth See Annex A5 Direction of speech Head erect6 Handset arrangement for listening See 2.3.77 Conditioning of carbon microp
45、hones Recommendation P.752.3.3 Vocal level of speakerThe vocal level at which speech is emitted from the speakers mouth conforms to that in use for determiningreference equivalents and is defined in Recommendation P.72 Red Book. This approximates the level actually used bycustomers under good transm
46、ission conditions. It is defined in terms of the speech level at the output of the NOSFERsending system.2.3.4 Listening levelThe level of received speech sounds at which loudness is judged constant is defined by the vocal level (see 2.3.3 above) and the setting (25 dB) of NOSFER against which all th
47、e speech paths shown in Figure 2/P.76 areadjusted. This corresponds to a fairly comfortable listening level of the same order as that commonly experienced bytelephone users.2.3.5 Handset positionThe position of the telephone handset relative to the talkers mouth is defined in Annex A to thisRecommen
48、dation. It is intended to approximate fairly well the position used by customers under real telephoneconnections. The definition covers not only the distance between lips and mouthpiece but also the attitude of themicrophone relative to the horizontal axis through the centre of the lips. It is defin
49、ed in such a way that the lips-to-mouthpiece distance becomes greater as the length of a handset is increased.2.3.6 Direction of speechThe speaker shall hold his head erect and it will be assumed that speech is emitted horizontally from his mouth.2.3.7 Handset arrangement for listeningThe listener shall hold the handset in his hand with the earphone placed comfortably against his ear.2.3.8 Conditioning of carbon microphonesTelephone handsets with carbon microphones usually require to be conditioned. This shall be done inaccordanc
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