1、BRITISH STANDARD BS 6840-18: 1996 IEC268-18: 1995 Sound system equipment Part 18: Peak programme level meters. Guide for digital audio level meter ICS 17.140.50; 33.160.30BS6840-18:1996 This British Standard, having been prepared under the directionof the Electrotechnical Sector Board, was published
2、 underthe authority of the Standards Board and comesintoeffect on 15 July 1996 BSI 07-1999 The following BSI references relate to the work on this standard: Committee reference EPL/100/3 Draft for comment 90/28744 DC ISBN 0 580 26108 5 Committees responsible for this British Standard The preparation
3、 of this British Standard was entrusted by Technical Committee EPL/100, Audio, video and multimedia systems and equipment, to Subcommittee EPL/100/3, Equipment and systems in the field of audio, video and audiovisual engineering, upon which the following bodies were represented: Association of Briti
4、sh Theatre Technicians Audio Engineering Society British Broadcasting Corporation British Educational Suppliers Association British Federation of Audio British Radio and Electronic Equipment Manufacturers Association British Telecommunications plc Federation of the Electronics Industry Independent T
5、elevision Association (ITVA) Institute of Sound and Communication Engineers Institution of Electrical Engineers International Association of Broadcasting Manufacturers Professional Lighting and Sound Association Royal National Institute for Deaf People Royal Institute of British Architects Society o
6、f Cable Television Engineers Amendments issued since publication Amd. No. Date CommentsBS6840-18:1996 BSI 07-1999 i Contents Page Committees responsible Inside front cover National foreword ii Introduction 1 1 General 1 1.1 Scope 1 1.2 Reference documents 1 2 Characteristics to be specified 1 2.1 Re
7、ference indication 1 2.2 Delay time 1 2.3 Return time 1 2.4 Other characteristics 1 3 Operating conditions 1 3.1 Temperature range 1 3.2 Supply voltage 1 4 Display 1 4.1 Display form 1 4.2 Display scale 2 4.3 Precision of indication 2 4.4 Peak level and indicated value 2 4.5 Other indications 2 5 In
8、terface 2 Annex A (informative) Other characteristics 3 Annex B (informative) Reading of meter indication and scale markingofanincremental display 3 Annex C (informative) Relation between signal processing precisionandtheindicating precision 4 Annex D Typical block diagram of a digital audio peak le
9、vel meter 5 Figure B.1 Reading of meter indication 3 Figure B.2 Scale marking of an incremental display 4 Figure D.1 Typical block diagram of a digital audio peak level meter 5 Table C.1 Relation between signal processing precision and indicatingprecision 4 List of references Inside back coverBS6840
10、-18:1996 ii BSI 07-1999 National foreword This Part of BS6840 has been prepared by Subcommittee EPL/100/3 and is identical with IEC 268-18:1995 Sound system equipment Part 18: Peak programme level meters Digital audio peak level meter, published by the International Electrotechnical Commission (IEC)
11、. IEC 268-18:1995 is a technical report type 3, which is collected data of a different kind from that which is normally published as an International Standard, and does not necessarily have to be reviewed until the data it provides is considered to be no longer valid or useful. BS 6840 consists of t
12、he following Parts: Part 1: Methods for specifying and measuring general characteristics used for equipment performance; Part 2: Glossary of general terms and calculation methods; Part 3: Methods for specifying and measuring the characteristics of sound system amplifiers; Part 4: Methods for specify
13、ing and measuring the characteristics of microphones; Part 5: Methods for specifying and measuring the characteristics of loudspeakers; Part 6: Methods for specifying and measuring the characteristics of auxiliary passive elements; Part 7: Methods for specifying and measuring the characteristics of
14、headphones and earphones; Part 8: Methods for specifying and measuring the characteristics of automatic gain control devices; Part 9: Methods for specifying and measuring the characteristics of artificial reverberation time delay and frequency shift equipment; Part 10: Methods for specifying and mea
15、suring the characteristics of peak programme level meters; Part 11: Specification for application of connectors for the interconnection of sound system components; Part 12: Specification for application of connectors for broadcast and similar use; Part 13: Guide for tests on loudspeakers; Part 14: G
16、uide for circular and elliptical loudspeakers; outer frame diameters and mounting dimensions; Part 15: Specification for matching values for the interconnection of sound system components; Part 16: Guide to the “RASTI” method for the objective rating of speech intelligibility in auditoria; Part 17:
17、Methods for specifying and measuring the characteristics of standard volume indicators; Part 18: Peak programme level meters. Guide for digital audio peak level meter. Cross-references Publication referred to Corresponding British Standard IEC 268.10:1991 BS 6840 Sound system equipment (HD 483.10 S1
18、:1993) Part 10:1991 Methods for specifying and measuring the characteristics of peak programme level meters (Identical) IEC 958:1989 BS EN 60958:1995 Specification for digital audio interface (EN 60958:1990) (Identical)BS6840-18:1996 BSI 07-1999 iii A British Standard does not purport to include all
19、 the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to i
20、v, pages1to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.iv blankBS6840-18:1996 BSI 07-1999 1 Introduction Digital processing of audio si
21、gnals is a common practice in the music industry, in audio equipment for consumer use and in broadcasting. It is necessary to monitor overload in digital sections after A/D conversion as well as overload in analogue sections in such digital equipment. The overload in a digital section, even if it oc
22、curs only instantaneously, produces very annoying distortion effects which cannot be compensated by level adjustment in a later section. Accordingly, check and measurement of the peak levels of both analogue and digital signals is an essential function of a digital audio system such as a digital aud
23、io mixer or a digital audio recorder. The indication of peak level of an analogue signal can be carried out by means of an analogue peak programme meter which is already standardized in IEC268-10. It is necessary to study a method to check, measure and to indicate the peak level of digital signals b
24、ecause such a standard has not previously been developed since digital equipment came on the market. It may be stated that the peak level of an analogue signal can also be measured by simply adding an A/D converter in front of such a digital audio peak level meter. The indicated peak level in fix ca
25、se may be slightly different from its true value; however, the accuracy of this method is sufficient for all practical purposes. In accordance with these considerations, this technical report offers specifications for the characteristics and performance of a peak digital coding level indicator, inte
26、nded to measure the peak level of a digital signal at any desired point of a digital audio signal system. 1 General 1.1 Scope This technical report describes a digital audio peak level indicator for professional and consumer use to indicate the peak levels of sampled and quantized audio signals. The
27、 purpose of this technical report is to establish a basic plan for standards development concerning the characteristics to be specified and the relevant methods of measurement for a digital audio peak level meter. 1.2 Reference documents IEC 268-10:1991, Sound system equipment Part10: Peak programme
28、 level meters. IEC 958:1989, Digital audio interface. 2 Characteristics to be specified 2.1 Reference indication The reference indication is the indication corresponding to the full-scale level of the circuit to which the indicator is connected. The indication on the scale shall be marked 0 in terms
29、 of decibels (dB). 2.2 Delay time The delay time is the time interval between the application of the reference input signal and the moment when the indicator passes a point 1dB below reference indication. This may include the time delay which occurs in the electronic circuit as a result of signal pr
30、ocessing. The delay time shall be less than 150ms. 2.3 Return time The return time is the time interval between the removal of a steady-state input signal (normally corresponding to the reference indication) and the moment when the indication passes a specified lower threshold of the scale. The retu
31、rn time shall be 1,7s 0,3s if the lower point is 20dB below reference indication. The return speed should be approximately constant. On instruments intended for monitoring multichannel programmes, the difference in return time should be less than 0,1s. When the maximum level is indicated on a numeri
32、cal indicator or in a special mode of the incremental display, the hold time shall be 1,0s 0,5s. NOTEIf the maximum peak value of the programme is to be held until it is manually reset, the indicator does not have to conform to the return time requirements. 2.4 Other characteristics See Annex A. 3 O
33、perating conditions 3.1 Temperature range The coding level meter shall function in a temperature range between 0 C and + 50 C. 3.2 Supply voltage The supply voltage to a meter shall be clearly identified. 4 Display 4.1 Display form Incremental dot or bar type displays or numerical displays shall be
34、used. They are used individually or in combination (including selectable display by a switch). The type of display should be clearly identified.BS6840-18:1996 2 BSI 07-1999 NOTENumerical indicators normally indicate the margin (headroom) in decibels from the digital full-scale level of 0 dB. On the
35、other hand, they are permitted to indicate codes or percentages of voltage values or decibels referred to 0,775 V (dBu) of the input analog signals, etc. 4.2 Display scale The full-scale indication of a display shall be 0. An example of an incremental bar type display is provided in Annex B. In the
36、case of numerical indicators, two types of display scales are recommended. The high precision type display shall have three digits (two digits before the decimal point and one digit after the decimal point, excluding negative sign display) with a maximum resolution of 0,1 dB. The low precision type
37、display shall have two digits (two digits before the decimal point, excluding negative sign display) with a maximum resolution of 1 dB. The type of display shall be clearly indicated. NOTEWhen another scale is used for the indication, the relation between indicated 0 dB on the scale and the referenc
38、e level (full-scale level) shall be indicated beside the display. 4.3 Precision of indication The precision shall be specified at the high range levels (0 to 20 dB) and at the low range levels (below 20 dB). NOTEAs the precision of indication is determined theoretically by the precision of the signa
39、l processing and scaling, the calculated precision value should be clearly marked (see Annex C). 4.4 Peak level and indicated value In the case of numerical indicators, the indication shall be 0 for the input signal corresponding to the reference level. Whenever the input level is lowered, the indic
40、ated value shall be maintained until the input signal level becomes the next lower indication level. The same relation applies to all levels which can be indicated. In the case of incremental indicators, the next lower level element and below shall be lit until the peak input level reaches the level
41、 to be indicated. The peak indication element shall be lit only when the input signal level reaches the indicated value. 4.5 Other indications When the input signal is pre-emphasized, the indication does not correctly correspond to the sound level. If the presence of pre-emphasis is flagged in the i
42、nput data stream, a clear display shall inform the user that the signal being monitored is pre-emphasized. Alternatively, a de-emphasis circuit may be employed prior to level indication; in this case it shall be clearly indicated that the indicator is de-emphasizing the signal being monitored. 5 Int
43、erface The interface to a digital audio peak level meter shall conform to IEC958. Excluded from this requirement is the case where the meter is incorporated in digital sound system equipment.BS6840-18:1996 BSI 07-1999 3 Annex A (informative) Other characteristics Digital level meters which do not in
44、clude any mechanical part, do not produce an error of integration time, overswing, or amplitude-frequency response with a practical significance. In spite of this fact, permitted values of these characteristics are provided here to match the form of this report to the form of IEC 268-10. A.1 Integra
45、tion time The duration of a burst of a 5kHz sinusoidal signal at reference level, which results in an indication2dB below reference indication. It shall be less than 5ms. A.2 Overswing The transient overshoot of the indication after a1000Hz input signal, which would result in 10 dB steady-state indi
46、cation, has been applied. A.3 Amplitude-frequency response The difference, expressed in decibels, between the indicated level and the input level as a function of frequency, referred to the value at a specified frequency, preferably 1000 Hz. It shall be within 0,5dB from 20Hz to 20kHz. However, a re
47、sponse irregularity may occur at specific frequencies related to the sampling frequency. The requirement therefore does not apply at these exceptional frequencies. The amplitude-frequency response shall be measured at a level which realizes the highest resolution on the indication scale. Annex B (in
48、formative) Reading of meter indication and scale marking of an incremental display Figure B.1 Reading of meter indicationBS6840-18:1996 4 BSI 07-1999 Annex C (informative) Relation between signal processing precision and the indicating precision The relation between the signal processing precision a
49、nd the indicating precision is given in Table C.1. Table C.1 Relation between signal processing precision and indicating precision This annex gives the results of fixed point processing, not floating point processing, and applies only to a16-bit system. Data for a system involving other than a 16-bit system may be obtained by calculation. Figure B.2 Scale marking of an incremental display Number of upper bits in processing absolute value codes (bits) level Indication precision Near maximum level dB Minimum
