1、ITU-T RECMN*P-38 93 .I LI862572 0584023 TOO INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU TELEPHONE TRANSMISSION QUALITY SUBSCRIBERS LINES AND SETS P.38 (03/93) TRANSMISSION CHARACTERISTICS OF OPERATOR TELEPHONE SYSTEMS (OTS) ITU-T Recommendation P.38 (P
2、reviously “CCITT Recommendation”) ITU-T RECNN+P.38 93 4862593 0584034 947 I FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issui
3、ng Recomrriendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on
4、these topics. ITU-T Recommendation P.38 was revised by the ITU-T Study Group XII (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 199
5、3. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in
6、 the text to references containing the acronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication administration and a recogni
7、zed operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1994 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfi
8、lm, without permission in writing from the ITU. ITU-T RECMN4P.38 93 m 4862591 0584015 883 m Recommendation P.38 TRANSMISSION CHARACTERISTICS OF OPERATOR TELEPHONE SYSTEMS (OTS) (Melbourne, 1988; amended at Helsinki, 1993) The measurement methods adopted for measuring on operator telephone systems (O
9、TS) which comprise a headset, feeding circuit and subscribers line (the same principles can be applied to any system that uses a headset), conform to the methods described in Recommendation P.64 with the following exceptions: 1 Sending sensitivities of OTS In principle, the OTS is similar to the Loc
10、al Telephone System (LTS) of Recommendation P.64 with the exception that in a headset the earphone and microphone may not have a fixed relationship as has a conventional telephone handset. Those headsets which are not adjustable in distance from the receiver to the microphone should be positioned pe
11、r Annex AP.76. For those which are adjustable, a modal position of the input port of the mouthpiece must be specified by the manufacturer in 3-dimensional coordinates relative to the lip, horizontal and vertical reference planes of the mouth as defined in Recommendation P.5 1. This modal position is
12、 defined by the manufacturer to be representative of the position of normal usage. NOTE - The term “corner of the mouth” used by some manufacturers in defining the normal use position is assumed to be 21 mm from the centre 9 mm behind the lip plane. The sound field of the artificial mouth is not def
13、ined behind the lip plane and therefore measurement points behind the lip plane are not recommended. The sending sensitivity is then determined as per clauses 2,4 and 6P.64 The sending loudness rating (SLR) is computed as described in Recommendation P.79. 2 Receiving sensitivities of OTS 2.1 For hea
14、dsets using supra-aural earphones, the Type 1 (see Recommendation P.57) artificial ear is used. The receiving sensitivity is determined as per clauses 3,5 and 7P.64. The receiving loudness rating (RLR) is computed as described in Recommendation P.79 using the LE values of Table 4P.79. 2.2 For headse
15、ts using insert type receivers, the Type 2 (see Recommendation P.57) ear simulator is used. The receiving sensitivity is determined as per clauses 3, 5 and 7P.64. 2.3 used. For headsets using intra-concha receivers, Type 3.1 (see Recommendation P.57) Concha bottom simulator is For headsets using low
16、 impedance supra-aural and supra-cocha receivers, Type 3.2 (see Recommendation P.57) Simplified pinna simulator is used. For headsets using supra-concha or supra-aural receivers which, due to their peculiar shape, do not fit the circular rims of Types 3.1 or 3.2 simulators, Type 3.3 Pinna simulator
17、see Recommendation P.57) is used. 2.4 The receiving sensitivity suitable for use in the calculation of loudness requires: a) a transfer function (SDE) for the eardrum to the ear reference point (ERP) and is given in Table laP.57; and b) the L(11 values of Table 1 appropriate for insert type receive
18、rs. Recommendation P.38 (03/93) 1 The sensitivity is defined as SJE = SJd SOE - LE(I) where SJE is the sensitivity from the junction to the real ear. SJd is the sensitivity from the junction to the type 2 (see Recommendation P.57) ear simulator (eardrum). LE(I) is the ear coupling loss of insert typ
19、e receivers (Table 1). SOE is the transfer function from the eardrum to the ERP (Table laP.57). The receiving loudness rating (RLR) is computed as described in Recommendation P.79 using SJE from the above formula. NOTES 1 2 The LE values of Table 4P.79 have been replaced by the values of Table 1. Fu
20、rther information on the measurement of OTS can be found in 3.4 of Handbook on Telephonometry. Frequency (Hz) 200 250 315 400 500 630 800 1 O00 1250 1600 2000 2500 3150 4000 TABLE 1P.38 Values of LE(I) for insert type receivers LECI) (dB) 23.0 19.0 18.0 17.4 12.8 9.0 6.8 3.2 1.5 1.4 0.4 -1.5 3.0 0.0 2 Recommendation P.38 (03/93)
