1、STD-ITU-T RECMN J-Zb-ENGL 1770 48b259L Ob3L7bli 425 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU J .26 (ex CMTT.645) (06/90) TELEVISION AND SOUND TRANSMISSION TEST SIGNALS TO BE USED ON CONNECTIONS INTERNATIONAL SOUND-PROGRAMME ITU-T Recommendation 5.26
2、 (Formerly Recommendation ITU-R CMTT.645) STD-ITU-T RECMN J-2b-ENGL 1990 Lidb257L Ob3L7b5 3bL FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff q
3、uestions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Rec
4、ommendations on these topics. ITU-T Recommendation 5.26 (formerly Recommendation ITU-R CMTT.645) was elaborated by the former ITU-R Study Group CMT. See Note 1 below. NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of
5、28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector (ITU-R). Conforming to a joint decision by the World Telecommunication
6、 Standardization Conference (Helsinki, March 1993) and the Radiocommunication Assembly (Geneva, November 1993), the ITU-R Study Group CMTT was transferred to ITU-T as Study Group 9, except for the satellite news gathering (SNG) study area which was transferred to ITU-R Study Group 4. 2 telecommunica
7、tion administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1990 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, i
8、ncluding photocopying and microfilm, without permission in writing from the ITU. Recommendation 5.26) TEST SIGNALS TO BE USED ON INTERNATIONAL SOUND-PROGRAMME CONNECTIONS (1 986; revised 1990) The CCIR, CONSIDERING that many impairments in international programme exchange on sound-programme connecti
9、ons are attributed that some existing definitions are found in different Recommendations of the CCIT and the CCIR; that for clarification, a list of those definitions should be available, (4 to different national test signal definitions; (bl (4 UNANIMOUSLY RECOMMENDS that for an international sound-
10、programme connection only the test signals defined below should be used: 1. Alignment signal (AS) Sine-wave signal at a frequency of 1 kHz, which is used to align the international sound-programme connection. The signal level corresponds to O dBuOs (see Note) (Le. 0.775 V r.m.s. at a zero relative l
11、evel point). In accordance with CCITT Recommendation N.13, the period of sending the alignment signal should be kept as short as possible - preferably to less than 30 s. Note - The notation “dBuOs” is defined in Recommendation 574. Other related texts of the CMTT use the notation “dBmOs” also define
12、d in Recommendation 574. 2. Measurement signal (MS) measurements and measurements at all frequencies (see CCITT Recommendations N. 12, N.13, N.21 and N.23). Sine-wave signal at a level 12 dB below the alignment signal level which should be used for long-term 3. Permitted maximum signal (PMS) Sine-wa
13、ve signal at 1 kHz, 9 dB above the alignment signal level, equivalent to the permitted maximum programme-signal level. The sound-programme signal should be controlled by the sending broadcaster so that the amplitudes of the peaks only rarely exceed the peak amplitude of the PMS. Note - Under these c
14、onditions a peak programme meter will indicate levels not exceeding the level of the permitted maximum signal. A numerical example may serve to clariQ this definition. The alignment signal has an r.m.s. voltage of 0.775 V and a peak amplitude of 1.1 V at a zero relative level point. The instantaneou
15、s peak amplitude of the sound-programme signal at this point should only rarely exceed 3.1 V. Although it is intended that the peaks of the sound-programme signal should not exceed the permitted maximum signal level, an overload margin must be provided so that rare excursions of the sound-programme
16、signal above the permitted maximum signal level may be tolerated. Note - Annex I describes the response of peak programme and vu meters to these test signals. 1 Formerly Recommendation ITU-R CMTT.645, Recommendation 5.26 (06/90) 1 STD*ITU-T RECMN J.2b-ENGL 1770 LiAb257L Ob327b7 13q D I1 Iiiii (-9) 2
17、 3 4 5 6 I (OIRT) (-21) I 1 I EC PPM type Ira I 1 I I I -a -4 Test 4 a IEC PPM I I I 1 I I 1 I I I type lib WU) Decibels I I (BBC) I -1 2 I - 20 -10 -a -6 -4 -2 o i 2 3 I II i111 IIII il Il Ili li li lu I I lili li li lilil I lililil il il II -20 -io -a -6 -4 -2 o i 2 3 (-12) I l I ANNEX I IlIll 7 I
18、 12 I I Vu meter (Australia, North America, etc.) Vu meter (France) ALIGNMENT USMG THE RECOMMENDED TEST SIGNALS WITH PEAK PROGRAMME METERS AND VU METERS 1. Broadcasters have evolved, over a period of forty years, procedures for using both types of meter to control programme levels. These procedures
19、are satisfactory to the organizations using them, so that they produce neither over-modulation, leading to distortion, nor under-modulation, leading to impairment from noise. Although different kinds of programme material deflect the two meters differently, the organizations using them have evolved
20、techniques that produce satisfactory level control and artistic balance within the programme. 2. The sensitivity of peak programme meters (PPM) is such that a sine wave signal at the alignment level, O dBuOs, indicates ?Test? on an EBU PPM (this corresponds to ?4? on the BBC PPM and ?-9? on the PPMs
21、 of the Federal Republic of Germany and the OIRT (see Fig. i). Measurement level (ML) 8 Permitted Alignment maximum level (AL) level (PML) FIGURE 1 - indications produced by various types of programme meter with the recommended test signals Note. - Meter indications are schematic - not to scale. do1
22、 -sc 3. full indication, O vu in Australia and North America and +2 vu in France (see Fig. i). The sensitivity of the vu meter is such that a sine wave signal at the alignment level, O dBuOs, produces nearly 4. The PPM reads ?quasi-peak?, that is, its peak indication on programme signals reads a lit
23、tle lower than true peaks. Operators are instructed to make the programme peaks give the same indication as a sinusoidal tone at +9 dBuOs (+8 dBuOs in some organizations). The true peaks of the programme are higher than indicated by up to 3 dB. When, additionally, operator errors are taken into acco
24、unt, the true peaks of the programme signal may reach the amplitude of a sinusoidal tone at +I5 dBuOs. 2 Recommendation 5.26 (06/90) STD-ITU-T RECMN J-2b-ENGL 1790 YBb259L Ob317b8 070 5. The vu meter indicates the mean level of the programme, which is generally much lower than the true peak. Operato
25、rs are instructed to make programmes peak generally to the O vu reading. Experience has shown that the true programme peaks are higher than indicated by between +6 dB and +13 dB, depending on the programme material. When, additionally, operator errors are taken into account, the true peaks of the si
26、gnal may be up to 16 dB higher than indicated, corresponding to the peak amplitude of a sinusoidal tone at +16 dBuOs, or alternatively +14 dBuOs when application of the alignment level signal results in +2 vu indication. 6. after control using either meter are very similar. Thus, although the dynami
27、c characteristics of the two meters are different, the highest peak levels encountered 7. Thus, an international connection between broadcasters will be correctly aligned regardless of the type of meter employed when a sinusoidal signal at alignment level, O dBuOs, produces the indication appropriat
28、e to that level at both the sending and receiving ends of the circuit. To avoid any confusion between alignment level and other levels that might be used, it is recommended that the three level tone test signal described in Recommendation 661 be used for the alignment of an intemational sound- programme connection. Figure i illustrates the indications given by a number of programme level meters when the recommended test signals are applied to them. Recommendation 5.26 (06/90) 3 -
