1、 International Telecommunication Union ITU-T P.360TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2006) SERIES P: TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Subscribers lines and sets Efficiency of devices for preventing the occurrence of excessive acoustic pres
2、sure by telephone receivers and assessment of daily noise exposure of telephone users ITU-T Recommendation P.360 ITU-T P-SERIES RECOMMENDATIONS TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Vocabulary and effects of transmission parameters on customer opinion of transm
3、ission quality Series P.10 Subscribers lines and sets Series P.30 P.300 Transmission standards Series P.40 Objective measuring apparatus Series P.50 P.500 Objective electro-acoustical measurements Series P.60 Measurements related to speech loudness Series P.70 Methods for objective and subjective as
4、sessment of quality Series P.80 P.800Audiovisual quality in multimedia services Series P.900 Transmission performance and QoS aspects of IP end-points Series P.1000 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. P.360 (07/2006) i ITU-T Recommendation P.360 Efficie
5、ncy of devices for preventing the occurrence of excessive acoustic pressure by telephone receivers and assessment of daily noise exposure of telephone users Summary It is known that an excessive acoustic pressure level may produce auditory damage to the users. To prevent the occurrence of excessive
6、acoustic pressure generated by the earphones of handset or headset, the telephony terminal equipment needs to implement devices to limit the acoustic pressure level. This Recommendation proposes limits to the acoustic pressure generated by the handset and headset earphones and some guidance on how t
7、o measure it. It also provides guidance on how to assess acoustic sound exposure of telephone users. It also includes some guidance to avoid speech degradation due to the use of devices implemented in the terminal to prevent the occurrence of excessive acoustic pressure. Source ITU-T Recommendation
8、P.360 was approved on 14 July 2006 by ITU-T Study Group 12 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. P.360 (07/2006) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommuni
9、cation Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembl
10、y (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which
11、fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this
12、 Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language
13、 such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Reco
14、mmendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of ap
15、proval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TS
16、B patent database. ITU 2006 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. P.360 (07/2006) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions and abbreviations. 1 4 Efficiency of protection a
17、gain excessive acoustic pressure 2 4.1 Efficiency of protection against short duration impulses. 2 4.2 Efficiency of protection against longer duration disturbances. 3 4.3 Assessment of 8-hour Daily Noise Exposure of telephone users. 3 5 Effect on normal speech signals . 6 Appendix I Alternative dai
18、ly noise exposure measurement . 7 I.1 Introduction 7 I.2 Description of the method 8 I.3 Headsets characterization . 9 I.4 Test set-up validation . 10 ITU-T Rec. P.360 (07/2006) 1 ITU-T Recommendation P.360 Efficiency of devices for preventing the occurrence of excessive acoustic pressure by telepho
19、ne receivers and assessment of daily noise exposure of telephone users 1 Scope The use of devices for preventing the occurrence of excessive acoustic pressure by telephone receivers is recommended in ITU-T Rec. K.7. Methods for checking the efficiency of such devices in response to short duration im
20、pulses, longer duration disturbances, such as tones, and Daily Noise Exposure are given in this Recommendation. A method is also given for checking that such devices do not have adverse effects on normal speech signals. 2 References The following ITU-T Recommendations and other references contain pr
21、ovisions 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; users of this Recommendation are therefore encouraged to investigate the poss
22、ibility 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. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recomm
23、endation. ITU-T Recommendation K.7 (1988), Protection against acoustic shock. ITU-T Recommendation O.6 (1988), 1020 Hz reference test frequency. ITU-T Recommendation P.57 (2005), Artificial ears. ITU-T Recommendation P.58 (1996), Head and torso simulator for telephonometry. ITU-T Recommendation P.38
24、0 (2003), Electro-acoustics measurements on headsets. IEC Publication 60711:1981, Occluded-ear simulator for the measurement of earphones coupled to the ear by ear inserts. IEC Publication 60950-1:2005, Information technology equipment Safety Part 1: General requirements. IEC Publication 61672-1:200
25、2, Electroacoustics Sound level meters Part 1: Specifications. IEC Publication 61672-2:2003, Electroacoustics Sound level meters Part 2: Pattern evaluation tests. 3 Definitions and abbreviations This Recommendation defines the following terms: 3.1 artificial ear: A device for the calibration of earp
26、hones incorporating an acoustic coupler and a calibration microphone for the measurement of the sound pressure and having an overall acoustic impedance similar to that of the average human ear over a given frequency band. 3.2 ear reference point (ERP): A virtual point for geometric reference located
27、 at the entrance to the listeners ear, traditionally used for calculating telephonometric loudness ratings. 3.3 ear-drum reference point (DRP): A point located at the end of the ear canal, corresponding to the ear-drum position. Relevant abbreviations in ITU-T Rec. P.10/G.100 apply. 2 ITU-T Rec. P.3
28、60 (07/2006) 4 Efficiency of protection again excessive acoustic pressure The testing methods provided in this Recommendation only cover the application of in-band signals, but the same sound pressure limits apply if ringing signals appear with the telephone set in off-hook conditions. On the basis
29、of the finding of scientific studies, several authors or organizations have proposed ear-damage risk criteria based on variations in acoustic pressure, under impulse conditions for which, parenthetically, there is no single definition. Likewise, ear-damage risk criteria have also been proposed for l
30、onger duration acoustic disturbances, such as tones. However, these criteria cannot be directly transposed to the test conditions and measurements described below. Nor could the results be cross-checked without introducing certain hypotheses that are not specified in this Recommendation, the purpose
31、 of which is merely to describe a method simple both in its application and in the analysis of the results obtained. The criteria recommended are based on experience gained in several countries about the telephone receiver quality necessary to ensure the safety of users and operators. Administration
32、s may wish to adopt lower limiting levels to reduce user annoyance caused by acoustic disturbances, but the limiting levels should not be so low as to have adverse effects on normal speech levels. ITU-T Recs P.57 and P.58 define several types of artificial ears. The use of the appropriate type of ar
33、tificial ear is determined by the size or the type of the earpiece of the handset or of the headset. 4.1 Efficiency of protection against short duration impulses In order to check whether a telephone set affords satisfactory protection against the risk of acoustic shocks due to short duration impuls
34、es, it is recommended that its characteristics be examined as follows: a) The entire telephone set, including the protective device, is placed in normal operating conditions and powered. b) Telephone sets with adjustable receive levels shall be adjusted to the maximum setting. c) The earpiece of the
35、 handset or headset earphone is applied to an artificial ear conforming to ITU-T Recs P.64 and P.380 respectively. d) The artificial ear is electrically connected to a measuring meter via a filter that carries out the DRP to Diffuse Field transfer function if Type 2 or 3 artificial ear is used. If T
36、ype 1 artificial ear is used, the filter should carry out the transfer functions from ERP to DRP and from DRP to Diffuse Field. The transfer functions between ERP to DRP and DRP to Diffuse Field are given by ITU-T Rec. P.58. The measuring meter can be any frequency analyser, sound pressure level met
37、er or simply a Noise Dose Meter that is capable of performing peak measurements. The measuring meter should be correctly calibrated and having the necessary circuits for the measurements. e) Electrical impulses are applied to the telephone set by a suitable assembly. For analogue two-wire terminals,
38、 the impulses are superimposed on the d.c. supply without the latter short-circuiting them. The 10/700-s surge generator specified in clause 6.2 of IEC 61000-4-5 shall be used. The open circuit voltage shall be 1000 volts, and the short-circuit current shall be 25 amps. For analogue four-wire system
39、s, the impulses are applied across the terminals of the receive circuit. f) The telephone set is also checked for self-generated acoustic impulses such as those produced by operation of the hook switch or by pulse dialling. g) For both cases e) and f) above, the peak acoustic pressure level observed
40、 (maximum instantaneous value) should be below the applicable national or regional safety regulations, e.g., U.S. Code of Federal Regulations, 29CFR1910.95 “Occupational noise exposure“ and the Directive 2003/10/EC of the European Parliament on the minimum health and safety requirements. ITU-T Rec.
41、P.360 (07/2006) 3 NOTE 1 It could be useful to repeat some tests more than one time, to ensure that the protection system is not damaged. NOTE 2 It is not necessary to test cordless phones for these short duration impulses. It is because in the longer duration disturbances test in 4.2 below, the tes
42、t signal through the cordless link is already at the maximum excursion. The required maximum sound pressure level for the longer duration disturbances is much lower than the requirement for this short duration impulses test. If a cordless phone can pass the test in 4.2, it implicitly passes this tes
43、t. 4.2 Efficiency of protection against longer duration disturbances In order to check whether a telephone set affords satisfactory protection against the risk of acoustic hazards due to longer duration disturbances, such as tones, it is recommended that its characteristics be examined as follows: a
44、) The entire telephone set, including the protective device, is placed in normal operating conditions as regards current supply and its position for the exchange of a call. b) Telephone sets with adjustable receive levels shall be adjusted to the maximum setting. c) The earpiece of the handset or he
45、adset earphone is coupled to an artificial ear in conformance with ITU-T Recs P.64 and P.380 respectively. d) The artificial ear is electrically connected to a measuring meter via a filter that carries out the DRP to ERP transfer function if Type 2 or 3 artificial ear is used. If Type 1 artificial e
46、ar is used, no correction filter shall be used. The measuring meter can be any frequency analyser, sound pressure level meter or simply a Noise Dose Meter that is capable of performing A-weighted sound pressure level measurements. The measuring meter should be correctly calibrated and be equipped wi
47、th the necessary circuits for carrying out the measurement. The transfer function between the measuring reference point to ERP is given by ITU-T Rec. P.57. The transfer function can also be taken in account by post processing if a filter is not used. NOTE 1 The maximum limits for these longer durati
48、on disturbances have been defined at ERP for many years. They have provided satisfactory protection against acoustic injury. The limits are then preserved as they have been historically proven. e) For analogue terminals, a swept sine wave signal across the band is applied to the telephone set. Its a
49、mplitude is increased until it reaches +15 dBV across the sets terminals or until the steady-state acoustic output from the telephone receiver reaches its limiting value, whichever occurs first. For digital terminals, a digitally encoded signal, e.g., square wave, representing the maximum energy deliverable by the network transmission system and/or by the coding system is used. f) The telephone set should also be checked for self-generated acoustic disturbances, such as tone dialling signals fed back to the receiver. g) For both cases e) and f) abo
