1、 I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n ITU-T G.100.1 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2015) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS International telephone connections and circuits Transmission planning and the E-model
2、 The use of the decibel and of relative levels in speechband telecommunications Recommendation ITU-T G.100.1 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 Transmission planning and the E-model G
3、.100G.109 General Recommendations on the transmission quality for an entire international telephone connection G.110G.119 General characteristics of national systems forming part of international connections G.120G.129 General characteristics of the 4-wire chain formed by the international circuits
4、and national extension circuits G.130G.139 General characteristics of the 4-wire chain of international circuits; international transit G.140G.149 General characteristics of international telephone circuits and national extension circuits G.150G.159 Apparatus associated with long-distance telephone
5、circuits G.160G.169 Transmission plan aspects of special circuits and connections using the international telephone connection network G.170G.179 Protection and restoration of transmission systems G.180G.189 Software tools for transmission systems G.190G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANA
6、LOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COO
7、RDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND
8、 USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.100.1 (06/2
9、015) i Recommendation ITU-T G.100.1 The use of the decibel and of relative levels in speechband telecommunications Summary Recommendation ITU-T G.100.1 provides the definition for different logarithmic power level measurement units in current use in telecommunication systems. This Recommendation als
10、o provides the relationship amongst those units and usage examples. The text herein is a merger of information that has been previously dispersed over several publications and supersedes the contents of: Recommendation ITU-T B.12, Annex A of Recommendation ITU-T G.100, Annex A of Recommendation ITU-
11、T G.101, Annex B of Recommendation ITU-T Q.551, and clause 3.8 of Recommendation ITU-T G.101. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.100.1 2001-11-29 12 11.1002/1000/5596 2.0 ITU-T G.100.1 2015-06-29 12 11.1002/1000/12504 _ * To access the Recommendation, type the
12、 URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T G.100.1 (06/2015) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency i
13、n the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication 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 s
14、tandardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (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 i
15、s covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which 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
16、 indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is a
17、chieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language 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. INTELLECT
18、UAL PROPERTY RIGHTSITU draws attention to the possibility that the practice or implementation of this Recommendation 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
19、 asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cauti
20、oned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2015 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of I
21、TU. Rec. ITU-T G.100.1 (06/2015) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation . 2 4 Abbreviations and acronyms 2 5 Conventions 2 6 Fundamentals about dB 2 6.1 Loss and gain 3 6.2 The letter “p“ in “dBmp
22、“ and “dBm0p“ . 5 6.3 Correction factors . 5 6.4 Signal-to-noise ratio . 7 6.5 Sound pressure level . 7 7 The use of a reference signal 7 8 Relationships between the units “dBm“,“dBr“ and “dBm0“ 9 8.1 General . 9 8.2 The unit “dB“ 10 8.3 The unit “dBm“ . 10 8.4 The unit “dBr“ 11 8.5 The unit “dBm0“
23、. 12 8.6 The relationship between dBm, dBr and dBm0 . 13 8.7 The unit “dBov“ 13 8.8 Relationship between overload (dBov) and maximum levels (dBm0) 14 9 The concept of “relative levels“ 15 9.1 General principles . 15 9.2 Circuits and connections . 16 9.3 The speech signal and the dynamic range of the
24、 voice channel . 17 9.4 Relative level designations for a digital path . 20 9.5 Relative levels in equipment design, specification and testing 21 9.6 Relative levels in transmission planning and maintenance 24 Appendix I The neper . 27 I.1 Introduction 27 I.2 Definition of the neper 27 I.3 Use of th
25、e decibel and of the neper 27 Bibliography. 28 Rec. ITU-T G.100.1 (06/2015) 1 Recommendation ITU-T G.100.1 The use of the decibel and of relative levels in speechband telecommunications 1 Scope In transmission engineering, most often it would be rather impractical to characterize the magnitude of si
26、gnals directly by a numerical value in volts or watts. Instead, a logarithmic measure is used, expressed in “dB“, to characterize the signal magnitude in relation to some chosen reference value. Designations commonly used are “power level difference“, “voltage level difference“, etc., all expressed
27、in “dB“. A level difference from a standard situation is described simply as “level“. Loss and gain are also measured in “dB“. The term “relative levels“ has been a very useful term in transmission planning for the last 40 years and is expected to be so in the future. However, the public switched te
28、lephone networks have changed considerably in these years. Especially with the introduction of digital exchanges which causes some uncertainty concerning the application of relative levels and necessitates some changes in the traditional way of applying relative levels. In this Recommendation, relat
29、ive levels and associated terms are explained and examples are shown to clarify these concepts. Guidance on the use of decibels in the field of sound transmission and radio frequencies can be found in ITU-R V.574-4. Notations for expressing the reference of a level can be found in Part 5 of IEC 6002
30、7-3. 2 References The following ITU-T Recommendations 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 re
31、vision; users of this Recommendation are therefore 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. The reference to a document within th
32、is Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.111 Recommendation ITU-T G.111 (1993), Loudness ratings (LRs) in an international connection. ITU-T G.121 Recommendation ITU-T G.121 (1993), Loudness ratings (LRs) of national systems. ITU-T G.223
33、Recommendation ITU-T G.223 (1988), Assumptions for the calculation of noise on hypothetical reference circuits for telephony. ITU-T G.711 Recommendation ITU-T G.711 (1988), Pulse code modulation (PCM) of voice frequencies. ITU-T G.712 Recommendation ITU-T G.712 (2001), Transmission performance chara
34、cteristics of pulse code modulation channels. ITU-T G.722 Recommendation ITU-T G.722 (2012), 7 kHz audio-coding within 64 kbit/s. ITU-T O.41 Recommendation ITU-T O.41 (1994), Psophometer for use on telephone-type circuits. ITU-T P.56 Recommendation ITU-T P.56 (2011), Objective measurement of active
35、speech level. 2 Rec. ITU-T G.100.1 (06/2015) ITU-T P.79 Recommendation ITU-T P.79 (2007), Calculation of loudness ratings for telephone sets. ITU-R V.574-4 Recommendation ITU-R V.574-4 (2000), Use of the decibel and the neper in telecommunications. IEC 60027-3 IEC 60027-3:2002, Letter symbols to be
36、used in electrical technology Part 3: Logarithmic and related quantities, and their units. IEC 60651 IEC 60651:1979, Sound level meters. 3 Definitions 3.1 Terms defined elsewhere None. 3.2 Terms defined in this Recommendation None. 4 Abbreviations and acronyms This Recommendation uses the following
37、abbreviations and acronyms: CLR Circuit Loudness Rating DRS Digital Reference Sequence FDM Frequency Division Multiplexing LR Loudness Rating MNRU Modulated Noise Reference Unit PBX Private Branch exchange PCM Pulse Code Modulation RLR Receive Loudness Rating RMS Root Mean Square SPL Sound Pressure
38、Level SLR Send Loudness Rating TRP Transmission Reference Point 5 Conventions None. 6 Fundamentals about dB The bel (symbol B) expresses the ratio of two powers by the decimal logarithm of this ratio. This unit is not often used, having been replaced by the decibel (symbol dB), which is one-tenth of
39、 a bel. The decibel may be used to express the ratio of two field quantities, such as voltage, current, sound pressure, electric field, charge velocity or density, the square of which in linear systems is proportional to power. To obtain the same numerical value as a power ratio, the logarithm of th
40、e field quantity ratio is multiplied by the factor 20, assuming that the impedances are equal. Rec. ITU-T G.100.1 (06/2015) 3 The relationship between a current or voltage ratio and that of the corresponding power ratio is impedance dependent. Use of the decibel when the impedances are not equal is
41、not appropriate unless adequate information is given concerning the impedances involved. The “dB“ is a very practical unit which can be used in many different applications. Comparing two signal powers P1 mVA and P2 mVA, P1 is said to be at an L dB higher (power) level than P2, where dB lo g 10 L21PP
42、 (6-1) Comparing two voltages, V1 volts and V2 volts, V1 is said to be at an L dB higher (voltage) level than V2, where dB lo g 20 L21VV (6-2) Note that “power“ depends on the square of “voltage“, hence the coefficient 10 in equation (6-1) and the coefficient 20 in equation (6-2). Equation (6-2) is
43、also used for quantities other than volts, for instance, currents, acoustic pressure, etc. Note that the term (V1/V2) must be a dimensionless quantity. This is automatically fulfilled when V1 and V2 represent two amplitudes of the same kind. Otherwise, V1 and V2 must each be referred to specific ref
44、erence values of the proper dimension. (For instance, the send sensitivity of a telephone set is described as the relationship between the input pressure in Pascal and the output voltage in volts, expressed as “dB rel. 1V/Pa“.) 6.1 Loss and gain The unit dB is also used to characterize loss or gain
45、(of power or voltage) in a system. Figure 1 shows how a voltage loss may be defined and calculated. The voltage loss is equal to the voltage level difference between port a) and port b). Figure 1 Example of voltage loss from port a) to port b) A special case is the return loss Ar which gives a measu
46、re of the mismatch between two impedances Z1 and Z2. (Ar can be described as the voltage loss between the incident and the reflected signal at the point of mismatch.) The expression for Ar is: dB lo g2021 21 ZZZZA r (6-3) For passive, reciprocal two-ports (like analogue, passive filters) it has been
47、 found practical to base the loss concept on the power level difference between the so-called apparent powers at the input and the output of the two-port. (It can be shown that for such types of circuits this definition of loss results in the same loss for both directions of transmission.) Figure 2
48、depicts the configuration. 4 Rec. ITU-T G.100.1 (06/2015) Figure 2 Example for apparent power loss calculation Note that the signal generator in Figure 2 produces a single-frequency tone. The reference apparent power P1 from the generator is defined to be obtained when the load is equal to the gener
49、ator impedance Z1. With the designation P2 for the output apparent power we get: 121ZEP222ZVP (6-4) Thus, the (apparent power) loss is: dB l o g20dB l o g102121 VEZZPPA (6-5) However, in telephone networks the transmission chain consists of cascaded units which contain amplifiers and 4-wire loops which are non-reciprocal and therefore the loss concept in equation (6-5) needs some modification in order to remain practical. As long as the impedan
