1、 Recommendation ITU-R BS.1771-1(01/2012)Requirements for loudness and true-peak indicating metersBS SeriesBroadcasting service (sound)ii Rec. ITU-R BS.1771-1 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency s
2、pectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunicat
3、ion Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent sta
4、tements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Recommendations (Also
5、 available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related sate
6、llite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management SNG Satellite news gathering TF Time sign
7、als and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2012 ITU 2012 All rights reserved. No part of this publication may be reproduced, by any
8、means whatsoever, without written permission of ITU. Rec. ITU-R BS.1771-1 1 RECOMMENDATION ITU-R BS.1771-1*Requirements for loudness and true-peak indicating meters (Question ITU-R 2/6) (2006-2012) Scope This Recommendation specifies some requirements for audio metering devices that implement the lo
9、udness and true-peak algorithms specified in other ITU-R Recommendations. The ITU Radiocommunication Assembly, considering a) that neither the VU meter nor a conventional peak programme meter gives an accurate indication of subjective loudness; b) that neither the VU meter nor a conventional peak pr
10、ogramme meter gives an accurate indication of the true-peak level of a digital signal; c) that listeners may desire the subjective loudness of audio programmes to be similar for different sources and different programme types; d) that the true-peak level of a digital signal may be larger than the ma
11、ximum sample value; e) that Recommendation ITU-R BS.1770 Algorithms to measure audio programme loudness and true-peak audio level, specifies the measurement of programme loudness and of true-peak levels; f) that the state of digital signal processing makes it practical to implement these algorithms
12、in a cost-effective metering device; g) that broadcasters have requirements that should be satisfied by meters used to indicate programme loudness and true-peak level, recommends 1 that audio meters employed to measure programme loudness, and/or to indicate true-peak level to assist in the avoidance
13、 of overload of digital audio signals, should meet the requirements specified in Annex 1 and Annex 2; 2 that Note 1 be considered as part of the Recommendation NOTE 1 Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.
14、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 such as “must” and the negative equivalents are used to express requirements. The use of such words shall in no
15、 way be construed to imply partial or total compliance with this Recommendation. *Radiocommunication Study Group 6 made editorial amendments to this Recommendation in October 2010 in accordance with Resolution ITU-R 1. 2 Rec. ITU-R BS.1771-1 Annex 1 Requirements for loudness and true-peak indicating
16、 meters Introduction The purpose of this Annex is to specify requirements for programme loudness and peak indicating meters. Scope This Annex outlines requirements for a meter designed for three purposes: a) For instrument-based prediction of subjective loudness of sound programme, measured over a s
17、hort term. b) For instrument-based prediction of subjective loudness of sound programme, measured over a longer period. c) Optionally, for indication of programme signal peaks. This meter may be used to assist a conventional meter or it may be used instead of a conventional meter. There shall be two
18、 categories of electronic display, called Type I and Type II. These displays shall differ only in resolution. The Type I display is intended for studio use. The Type II display is intended for portable equipment where size, weight and power consumption must be minimized. Definitions Loudness unit (L
19、U) The loudness unit is the scale unit of the loudness meter. The value of the programme in loudness units represents the loss or gain (dB) that is required to bring the programme to 0 LU, e.g. a programme that reads 10 LU will require 10 dB of gain to bring that programme up to a reading of 0 LU. M
20、omentary loudness Momentary loudness is defined as the ungated loudness in Recommendation ITU-R BS.1770 loudness algorithm when passed through a first-order IIR (infinite impulse response) low-pass filter with a 400 ms time-constant, as described in further detail in Annex 2 of this Recommendation.
21、Short-term loudness Short-term loudness is defined as the ungated loudness in Recommendation ITU-R BS.1770 loudness algorithm when integrated over an interval of 3 seconds, as described in further detail in Annex 2 of this Recommendation Type I electronic display Electronic display with a resolution
22、 of one or more segments per loudness unit. Type II electronic display. Electronic display with a resolution of one segment for 3 loudness units. Rec. ITU-R BS.1771-1 3 TABLE 1 Requirements for loudness and peak indicating meters (General requirements) Req No. Requirement Additional description Req/
23、Opt PLG-1 The loudness meter may incorporate a display for peak level indication Optional PLG-2 The loudness meter may have one or more of the following operating modes: M mode (momentary), S mode (short), and I mode (integrated). Optional PLG-3 The loudness display reading must not vary by more tha
24、n 0.5 loudness units when the signal polarity is reversed Required PLG-4 The integration mode may provide a time-averaged reading over a fixed time interval. The time interval should be manually selectable with a start/stop button or switch. A meter with an integration mode should have a numerical d
25、isplay accompanied optionally, by a bar graph or moving needle display Optional NOTE The fast mode described in an earlier revision of this Recommendation is now deprecated. TABLE 2 Common requirements for programme loudness displays Req No. Requirement Additional description Req/Opt PLD-1 The loudn
26、ess display may be a moving indicator mechanical type, an array or multi-segment electronic type Optional PLD-2 The loudness display shall show units at all times, that is, either LU or LKFS1as appropriate Required PLD-3 The loudness display scale may change colour or intensity at 0 LU Optional PLD-
27、4 The loudness display scale should have one of two ranges: from 18LU to +9LU or from 36LU to +18LU (or the equivalent on an absolute LKFS scale). The scale shall be linear in these ranges further study Optional PLD-5 Loudness of a stereo or multi-channel sound programme shall be shown by a single d
28、isplay. (This does not prevent meters from also displaying individual channel loudnesses.) Required 1LKFS: Loudness K-weighed relative to nominal Full Scale. 4 Rec. ITU-R BS.1771-1 TABLE 3 Requirements for programme loudness display mechanical type Req No. Requirement Additional description Req/Opt
29、MCD-1 A mechanical loudness meter display shall have a non-linearity of not more than 1% of full-scale deflection over its operating range Required TABLE 4 Display requirements Optional peak level indicator on loudness meter Req No. Requirement Additional description Req/Opt PLI-1 The digital overlo
30、ad indication should consist of one red indicator Optional PLI-2 The threshold for overload indication shall be 2 dB re full scale digital input Required PLI-3 The overload indicator shall activate if the true-peak digital audio level exceeds the threshold Required PLI-4 Once the indicator light is
31、activated it shall remain activated for at least 150 ms after the signal has fallen below the threshold Required Rec. ITU-R BS.1771-1 5 Appendix 1 to Annex 1 (informative) Example of programme loudness display FIGURE 1 Example of programme loudness display, mechanical type BS.1771-01+9+6+3-3-6-9-12-
32、15-18RefPeakP rogram meloudness+06.0ModeOptionalOptionalStart/StopSAllISpeechMLU6 Rec. ITU-R BS.1771-1 FIGURE 2 Example of programme loudness level display, opto-electronic Type I BS.1771-02+9+6+3Ref-3-6-9-12-15-18PeakProgrammeloudnessLUModeStart/StopSAllISpeech+09.0OptionalOptionalMRec. ITU-R BS.17
33、71-1 7 FIGURE 3 Example of programme loudness level display, opto-electronic Type II BS.1771-03+9+6+3Ref-3-6-9-12-15-18PeakModeStart/StopSAllISpeechProgrammeloudness+09.0OptionalOptionalMLU8 Rec. ITU-R BS.1771-1 Appendix 2 to Annex 1 (Informative) Explanatory notes 1 Background and terminology Loudn
34、ess is a perceptual property of an audio signal when it is reproduced acoustically. It is a complex, non-linear function of amplitude, frequency and bandwidth. Level is the amplitude of a signal either the r.m.s. voltage of an electrical signal or the sound pressure of an acoustical signal. It is an
35、 objective property which is independent of frequency and bandwidth and can be measured linearly in volts if electrical, or Pascals if acoustical, or logarithmically in decibels (dB) with respect to a stated reference level. For the purposes of broadcasting, loudness can also be measured as an elect
36、rical property, assuming a fixed electro-acoustic gain for reproduction. This assumption is the basis for the broadcast loudness meter specified in Recommendation ITU-R BS.1770. The reproduction level that has been assumed in the home is 60 dBA, a level found by Benjamin to be a typical listening le
37、vel for television viewing in actual homes Benjamin, 2004. Recommendation ITU-R BS.1864 specifies a target operating loudness level of 24 LKFS. Some organizations may specify operation at different levels. The chosen operating loudness level corresponds to 0 LU on a loudness meter that indicates rel
38、ative loudness. A broadcast loudness meter has a combination of the following three operating modes: M mode (momentary), S mode (short), and I mode (integrated). These are used for different purposes. Momentary and short-term modes are used in production, post-production and presentation. The progra
39、mme level should be set so that for the full programme mix, or anchor element of the programme content (typically dialogue), the meter should display 0 LU on average. Integrating mode is used for quality control, mainly at programme ingestion, programme emission and in post-mortem analysis. The sing
40、le-number output from this mode allows clear and unambiguous information for loudness-matching and gain setting. 2 Meter display format A fundamental decision is whether the display should use a mechanical meter, an electronic display or whether it should be specified to allow implementation in eith
41、er format. Although many operators prefer electronic displays, and these are increasingly common on digital sound and video equipment, some operators, especially visually impaired operators, prefer a mechanical meter. The requirement has therefore been written to cover both types of implementation.
42、3 Signal type discrimination Another fundamental decision is whether the meter includes a selectable mode whereby it can recognize speech and only actively measure during those time-periods when the signal is primarily speech/dialogue. Rec. ITU-R BS.1771-1 9 While it can be useful to know the loudne
43、ss of isolated elements of the audio signal such as speech, it is difficult to specify the performance of such a facility, and it is often desirable to know the overall loudness. Therefore, the primary mode of the meter has no speech discrimination. An optional secondary mode may allow speech discri
44、mination; this mode can be useful to help measure dialogue level. 4 Multi-channel metering As our perception of loudness is independent of the number of sound sources involved, a single level display is sufficient to indicate the loudness for multi channel sound systems. If level displays are includ
45、ed for the individual input channels, the true peak level indicator must be driven by the maximum value that was measured across all input channels. This does not interfere with the usual practice of separate level metering for each channel, as separate level/peak meters may be provided for the indi
46、vidual channels. 5 Peak level indicator (optional) a) Ergonomics There can be ergonomic difficulties with presenting two sets of information (relative loudness and peak level) on a single meter display. More information is not always better. Consideration should be given to the meter design to ensur
47、e that peak levels are not confused with loudness levels. If a meter is to present two sets of information it is preferable to have a primary display giving detailed information and a secondary display giving less information as a warning rather than as a measurement. For this reason, on a meter pri
48、marily intended to show programme loudness, the information presented by the peak level display is less than the information displayed by a conventional peak programme meter b) Hold time of peak indicator lights A minimum hold time of 150 ms was chosen as a long enough time for the light to register
49、 with the eye, as very brief indications will look quite dim otherwise. c) Option for separate level metering While the form of the peak indication on the loudness meter is mandatory, the peak indication feature itself is not mandatory. This Recommendation is not intended to alter existing level metering practices it is intended as an adjunct to them. It is expected that in most situations, separate level metering on each channel will be retained, removing the need for peak indication on the loudness meter. d) Metering in recording In the application of setting lev
