ITU-R BS 645-2-1992 Test Signals and Metering to Be Used on International Sound Programme Connections - Section 10C - Audio-Frequency Characteristics of Sound-Broadcasting Signals《.pdf

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1、Rec. 645-2 25 RECOMMENDATiON 645-2* TEST SIGNALS AND METERING TO BE USED ON INTERNATIONAL SOUND PROGRAMME CONNECTIONS (Questions 82/10 and 19/CMTT) (1986-1990-1992) The CCIR, eo nside ring that many impiirtnents in international programme exchange on sound-programme connections are attributed that s

2、ome existing definitions are found in different Recommendations of the CCIT and the CCIR; that for clarification, a list of those definitions should be available, a) to different national test signal definitions and methods of metering; b) cl recommends that for an international sound-programme conn

3、ection only the test signals defined below should be used, in conjunction with methods of metering described in Annexes 2 and 3. 1. Alignment signal (AS) Sine-wave signal at frequency of 1 kHz which is used to align the international sound-prograuirne connection. The signal level corresponds to O dB

4、uOs (see Note 1) (i.e. 0.775 V r.m.s. at a zero relative level point). In accordance with CCITT Recommendrition N.13, the period of sending the alignment signal should be kept as short as possible - preferably to less than 30 s. Note I - The notation “dBuOs” is defined in Recommendation 574. Other r

5、elated texts of the CMTT use the notation “dBmOs” also defined in Recommendation 574. 2. Measurement signal (MS) measurements and measurements at all frequencies (see CCIT Recommendations N.12, N.13, N.21 aid N.23). Sine-wave signal at a level 12 dB below the alignment signal level which should be u

6、sed for long-term 3. Permitted maximum signal (PMS) Sine-wave signal at 1 kHz, 9 dB above the alignment signal level, equivalent to the permitted m,axiUium programme-signal level. The sound-programme signal should be controlled by the sending broadcaster so that the ainplitudes of the peaks only rea

7、lly exceed the peak amplitude of the PMS. Note I - Under these conditions a peak programme meter will indicate levels not exceeding the level of the permitted maximum signal. A numerical example may serve to clarify this definition. The alignment signal has an r.m.s. voltage of 0.775 V and a peak am

8、plitude of 1.1 V at a zero relative level point. The instantaneous peak amplitude of the soutid- progrCamme signal at this point should only rarely exceed 3.1 V. Ahhough it is intended that the peaks of the sound-programme signal should not exceed the permitted maximum signal level, an overload marg

9、in must be provided so that rare excursions of the sound-progr,uime signal above the permitted m,utimum signal level may be tolerated. * The CMTT and Study Group 10 will coordinate the future developmeut of this Recommeudatioii. This Recoinuieudatiou should be brought to the attention of Study Group

10、 IV of the CCITT. CCIR RECMNub45-2 92 H 4855212 0519255 130 26 Rec. 645-2 Note 2 - Annex 1 describes the response of peak programme and vu meters to these test signals. Annex 2 describes the principal characteristics of the various insmments used for monitoring the volume of peaks during programme t

11、ransmissions. Annex 3 gives an explanation of dBuOs and dBrs terminology. Alignment using the recommended test signais 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 proc

12、edures 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 e

13、volved 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 t

14、he PPMs of the Federal Republic of Germany and the OIRT (see Fig. i). FIGURE 1 Indications produced by various types of programme meter with the recommended test signals Measurement level (ML) t Alignment level (AL) t Permitted maximum level (PML) f Od B 5d B I-20dB -10dB -5dB I EC PPM type I (FRG)

15、I I IIIIIIIIIJ (-9) (OIRT) I Kar. type I II I I I I 1 2 3 4 5 IEC PPM -1 2 -8 -4 Test 4 8 12 PPM I I I 1 I I I I I 1 I 1 I I I I I Decibels (BBC) I type IIa IEC type IIb (EBU) -20 1 -10 -8 -6 -4 -2 O 1 2 3 I I I I II II III I II illll Ill1 11.1 I I (-12) I -20 -lO -8 -6 -4 -2 O 1 2 3 I I I 11 I I 11

16、 I I I I I I 111 I 111 11 41 11 I I Vu meter (Australia, North America, etc.) Vu meter (France) Nofe I - Meter indications are schematic -not to scale. CCIR RECMN*b45-2 92 4855212 0519256 077 Rec. 645-2 27 3. nearly full indication, O vu in Australia and North America and +2 vu in France (see Fig. 1

17、). The sensitivity of the vu meter is such that a sine-wave signal at the alignment level, O dBuOs, produces 4. The PPM reads “quasi-peak”, that is, its peak indication on programme signals reads a little lower than true peaks. Operators are instructed to make the programme peaks give the same indic

18、ation 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 account, the true peaks of the programme signal may reach the amplitude of a sinusoidal tone at +15 dBu

19、Os. 5. The vu meter indicates the mean level of the programme, which is generally much lower than the true peak. Operators 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, d

20、epending on the programme material. When, additionally, operator errors are taken into account, the true peaks of the signal may be up to 16 dB higher thcm indicated, corresponding to the peak amplitude of a sinusoidal tone at +16 dBuOs, or alternatively +14 dBuOs when application of the alignment l

21、evel signal results in +2 vu indication. 6. encountered after control using either meter are very similar. Thus, although the dynamic characteristics of the two meters are different, the highest pe, a +6 dBu signal occurring at a +6 dBr point is also a O dBuO signal; a -6 dBu signal occurring at a +

22、6 dBr point is a -12 dBuO signai, and so on. Levels expressed in dBuO correspond to measurements referred to in the alignment signal. 3.4 dBrs arid dBuOs CCITT Study Group XV has proposed that the suffix Y be added to the terms dBuO and dBr when these refer to sound programme transmission and not to

23、 telephone circuits. The “s” may be used where necessary in broadcasting practice to avoid confusion. It is therefore evident that: - dBu (voltage level) = dBuOs (normalized test signal level) + dBrs (normalizing factor). The addition sign must be taken to indicate algebraic addition. Note 1 - The dBrs value is determined by circuit gain or loss. -