1、 STD-ITU-T RECMN P-370-ENGL L99b m 48b2591 Ob24L1 b2T INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU P.370 (08/96) SERIES P: TELEPHONE TRANSMISSION QUALITY Subscribers lines and sets Coupling Hearing Aids to Telephone sets ITU-T Recommendation P.370 (Prev
2、iously “CCITT Recommendation”) STD-ITU-T RECMN P-370-ENGL 379b 48b2571 Ob24302 5bb ITU-T P-SERIES RECOMMENDATIONS TELEPHONE TRANSMISSION QUALITY Vocabulary and effects of transmission parameters on customer opinion of transmission quality P. 10-P.29 Subscribers lines and sets Transmission standards
3、Objective measuring apparatus Objective measuring apparatus Objective electro-acoustical measurements Measurements related to speech loudness Methods for objective and subjective assessment of quality Methods for objective and subjective assessment of quality l P.30-P.39 P .40-P.49 P.500-P.599 P.50-
4、P.59 P.60-P.69 P.70-P.79 P.800-P.999 P.80-P.99 For further details, please refer to ITU-T List of Recommendations. - STD-ITU-T RECMN P-370-ENGL L77b 48b257L Ob24103 4T2 FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (IT
5、U). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the
6、 topics for study by the IT-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). IT-T Recommendation P.370, was prepared b
7、y IT-T Study Group 12 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 30th of August 1996. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1
8、997 Ail 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 microfilm, without permission in writing from the IT. Recommendation P.370 (08/96) 1 . STD-ITU-T RECMN P.370-ENGL L77b 48b257L Ob24104
9、337 CONTENTS 1 Scope 2 Normative references . 3 Definitions and abbreviations . 3.1 Definitions 3.2 Abbreviations Magnetic field strength around the earcap of telephone handsets which provide for coupling to hearing aids . 4.1 Introduction 4.2 Magnetic field strength measurements and recommended val
10、ues Calibration of acoustic receive level . Magnetic field strength level . Linearity of the magnetic field strength Measurement of frequency characteristics 4 4.2.1 4.2.2 4.2.3 4.2.4 4.3 Probe coil 4.3.1 Dimensions . 4.3.2 Calibration of the probe coil . 4.3.3 Distortion Characteristics of telephon
11、e sets that provide additional amplification for the benefit of hearing impaired users . 5.1 Introduction 5.2 Sending characteristics . 5.2.1 Sensitivity . 5.2.2 Frequency response . 5.3 Receiving characteristics 5 5.3.1 Sensitivity . 5.3.2 Frequency response . 5.3.3 Restoring normal receive amplifi
12、cation 5.4 Sidetone Electrical coupling of telephone sets to hearing aids . 6.1 Introduction 6.2 Electrical characteristics . Point of connection in the telephone set . Electrical characteristics at interconnection point . 6 6.2.1 6.2.2 6.3 Interconnection with the telephone set . 6.3.1 Connector ty
13、pe 6.3.2 Connector position Page 1 1 2 2 2 2 2 3 3 4 4 4 5 5 5 5 6 6 6 6 6 7 7 7 7 7 8 8 8 8 8 9 9 9 6.4 Safety issues 9 A.1 Measurement procedures 10 A.2 Magnetic field requirements 10 A.3 Physical properties 10 Annex A - Measurement of an acousto-magnetic adapter generating a magnetic field 10 . A
14、ppendix I - Examples of frequency characteristics of hearing aids coupled to telephones Appendix II - Bibliography . 10 15 11 Recommendation P.370 (08/96) STD-ITU-T RECMN P.37U-ENGL 177b 48b2571 Ob24105 275 m SUMMARY This Recommendation has been updated from Recommendation P.37, Coupling Hearing Aid
15、s to Telephone sets. Clause 4 covers inductive coupling and is technically similar to the original Recommendation P.37. Clause 4 however now includes the relevant figures that were previously referred out to other Recommendations. It presents recommended levels and frequency characteristics for the
16、inductive field at the telephone earphone relative to a sound level presented at the same earphone. Clause 5 covers additional amplification that may be provided for the benefit of hearing impaired users, and only editorial changes have been made to the text originally contained in Recommendation P.
17、37. Limits for the additional amplification and range of volume control are given. Frequency response is also covered. Clause 6 introduces the possibility of electrical coupling of a telephone set to a hearing aid. It is compatible with IEC Publication 11 8 Part 6, which covers the characteristics o
18、f hearing aid electrical input circuits. The electrical output level relative to the sound level in the same telephones earphone is given in this Recommendation, together with frequency response, source impedance and maximum output level. Technically this Recommendation is compatible with similar do
19、cuments recently drafted within ETSI covering the same subjects . . Recommendation P.370 (08/96) 111 FOREWORD It is recognized that there is a sizeable proportion of telephone users that have difficuly in conversing over a telephone connection due to hearing loss. To alleviate these difficulties spe
20、cial means have been provided in many national systems to enable hearing impaired users to couple their hearing aids inductively to the telephone receiver, and a number of nationaYintemationa1 specifications define Characteristics for this form of coupling. Clause 4 addresses the requirements for su
21、ccessful inductive coupling of hearing aids to telephone sets. Furthermore, it is also recognized that many hearing impaired users are able to have satisfactory telephone conversations while coupling their hearing aids acoustically to the telephone receiver, or even using the telephone handset witho
22、ut a hearing aid. This latter situation is possible due to the fact that under good conditions a telephone connection can be louder than a face-to-face conversation over a one-metre air path by up to 30 dB. Provision of additional amplification in the mouth-to-ear path can greatly increase the propo
23、rtion of telephone conversations involving hearing impaired users that are rated “good”. Clause 5 addresses this form of coupling. Certain national standards also exist to enable direct electrical connection of hearing aids to telephone apparatus. This form of coupling is addressed in clause 6, and
24、has been written to be compatible with the IEC Publication 118-6, 1984, covering the characteristics of electrical input circuits for hearing aids. NOTES 1 2 Care should be taken when designing hearing aids to include sufficient immunity to radio frequency interference to avoid disturbances arising
25、from the detection of radio signals emitted by cordless and mobile telephones. Tests have shown that telephone earphones having low acoustic impedance, which exhibit less low frequency loss due to leakage effects, couple acoustically very well into hearing aids by presenting a much flatter overall f
26、requency characteristic to the ear of the user than conventional earphones having high acoustic impedance. iv Recommendation P.370 (08196) STD-ITU-T RECMN P-370-ENGL 199b m 48b2571 Ob24107 OL18 m Recommendation P.370 COUPLING HEARING AIDS TO TELEPHONE SETS (Geneva, 1996) 1 Scope Clause 4 applies to
27、telephone handsets having supra-aural earphones that can be connected to the Public Switched Telephone Network (PSTN) or the Integrated Services Digital Network (ISDN) which are intended for direct application to the ear (e.g. traditional handsets, operators headsets) and which provide a magnetic fi
28、eld for coupling to hearing aids. It specifies the level, linearity and frequency dependence of the magnetic field strength produced by the handset and characteristics for the calibrated probe coil. Clause 5 specifies the electro-acoustic performance Characteristics of telephony terminals which are
29、intended for direct application to the ear (e.g. traditional handsets, operators headsets) and which provide, at the earphone, additional amplification in the receiving direction compared with the Receiving Loudness Rating (RLR) specified in the requirements of the national system. Clause 6 specifie
30、s the electrical characteristics for the electrical coupling of the telephony function, implemented telecommunication terminal equipment, to hearing aids. It specifies the level and f-equency response relative to the acoustic output at the earphone, also the noise and maximum level. Annex A specifie
31、s the measuring method for an acousto-magnetic adapter that converts the acoustic output of an associated telephone receiver to a magnetic field, in accordance with 4.2.1 and 4.2.2, that can be received by the magnetic pick-up coil in a hearing aid. 2 Normative references The following Recommendatio
32、ns, and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommendation are there
33、fore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. IEC Publication 118-6: 1984, Hearing aids - Part 6: Characteristics of electrical i
34、nput circuits for hearing aids. IT-T Recommendation P.10 (1993), Vocabulavy of terms on telephone transmission quality and telephone sets. IEC Publication 118-4: 1981, Hearing aids - Part 4: Magnetic field strength in audio-frequency induction loops for hearing aidpurposes. IEC Publication 1 18- 1 :
35、 1995, Hearing aids - Part 1: Hearing aids with induction pick-up coil input. IT-T Recommendation P.340 (1996), Transmission characteristics of hands-ee telephones. ITU-T Recommendation G.121 (1993), Loudness Ratings (La) of national systems. IEC Publication 130-8: 1976, Connectors forj-equencies be
36、low 3 A4Hz -Part 8: Concentric connectors for audio circuits in radio receivers. IEC Publication 268-11: 1987, Sound system equipment - Part il: Application of connectors for the interconnection of sound system equipment. ITU-T Recommendation P.57 (1993), Artificial ears. CCITT Recommendation P.48 (
37、1988), Specification for an intermediate reference system. - - - - - - - - - - I) Previously Recommendation P.37 Recommendation P.370 (08/96) 1 3 Definitions and abbreviations 3.1 Definitions The relevant definitions given in Recommendation P.10 apply along with the following: 3.1.1 given in 4.2.2.
38、The units are amperes per metre (Alm). level of magnetic field strength: the maximum level of the magnetic field strength and its measurement are 3.1.2 plane of measurement: A plane parallel to the earcap at a distance of 10 mm. 3.1.3 surface of the acousto-magnetic adapter opposite the earcap conne
39、ction. The adapter plane: It is defined as the plane formed by the contacting points of a flat surface against the 3.2 Abbreviations For the purposes of this Recommendation, the following abbreviations are used. AGC Automatic Gain Control DRP Dm Reference Point ERP Ear Reference Point HATS Head and
40、Torso Simulator IEC International Electrotechnical Commission IRS Intermediate Reference System ISDN Integrated Services Digital Network LSTR Listener Sidetone Rating OLR Overall Loudness Rating Pe PSTN Public Switched Telephone Network RLR Receiving Loudness Rating SLR Sending Loudness Rating STMR
41、Sidetone Masking Rating TCL Terminal Coupling Loss Sound pressure level at the ERP 4 Magnetic field strength around the earcap of telephone handsets which provide for coupling to hearing aids 4.1 Introduction Magnetic induction systems incorporated in telephone handsets generate an alternating magne
42、tic field with spatial characteristics which make the field detectable by hearing aids equipped with induction pick-up coils. Reception of an audio-frequency signal via an induction pick-up coil can often allow an acceptable signal-to-noise ratio to be achieved in cases where the acoustical receptio
43、n would otherwise be degraded by background noise. The magnetic field strength which enables induction pick-up coils in hearing aids to function effectively must be high enough to produce an acceptable signal-to-noise ratio but not so high as to cause overloading of the hearing aid. 2 Recommendation
44、 P.370 (08/96) The value of the magnetic field strength recommended in this Recommendation has been chosen so that these requirements are met as far as possible. (See Bibliography 11 for a discussion on end-to-end levels that can be expected for hearing aid users coupled inductively to a telephone s
45、et. This can be compared with the preferred listening levels for users having normal hearing 2). Information on the measurement of an acoustic-magnetic adapter generating a magnetic field is found in Annex A. 4.2 Magnetic field strength measurements and recommended values 4.2.1 Calibration of acoust
46、ic receive level Using the measurement configuration shown in Figure 1 for analogue telephones, Figure 2 for digital telephones, the drive level of the oscillator shall be adjusted to produce a sound pressure level of -14 a firm contact to the earcap so that the acousto-magnetic adapter and the tele
47、phone handset can be used as an integral unit; forming a good and well-defined acoustic coupling to the earcap (see Note); the surface of the acousto-magnetic adapter defining the adapter plane should be flat or should have a shape easily defining the adapter plane; the adapter plane should be appro
48、ximately parallel to the earcap plane; the magnetic field produced by the adapter should be orientated so that the magnetic coupling to the hearing aid is only to a small extent dependent on the position of the hearing aid. NOTE - The inner diameter of an acoustic seal is recommended to be equal to
49、the edge diameter of the IEC 3 18 artificial 0 ear (see Recommendation P.57). Appendix I Examples of frequency characteristics of hearing aids coupled to telephones (This appendix does not form an integral part of this Recommendation) Figures 1.1 to 1.9 have been taken from i and illustrate the signals arriving at the Drum Reference Point (DRP) of a Head And Torso Simulator (HATS). Figure 1.2 refers to the IRS (see Recommendation P.48) sending and receiving ends joined directly together and having an OLR by definition of O dB. All other fi
