Measurements in digital component television studios 625–line systems at the 4:2:2 and 4:4:4 levels using parallel and serial interfaces (SDI) Tech. 3283–E December 1996 CONTENTS Acknowledgement. 2 Introduction. 3 Important notes. 4 Chapter 1 Presentation of digital component interfaces. 5 1.1. The 4:2:2 digital video format . 5 1.2. Other digital component signal formats . 8 1.3. Other standards to be considered . 9 1.4. Physical interfaces for digital component video signals . 10 Chapter 2 Measurements in the analogue domain. 13 2.1. A/Dser and Dser/A converters for video and audio signals . 13 2.2. Analogue video before and after digital processing . 15 Chapter 3 Measurements in the data domain. 23 3.1. Video signal . 23 3.2. Timing reference signals (TRS) . 26 3.3. Ancillary data . 27 3.4. Conversion between 8–bit and 10–bit representations . 27 3.5. Most important measurements in the SDI data domain . 28 Chapter 4 Measurements in the physical domain. 29 4.1. Parallel interface . 29 4.2. Serial interface . 32 Chapter 5 System aspects. 43 5.1. Relative timing between video and audio – General considerations . 43 5.2. Relative timing between video and audio signals in the analogue domain . 44 5.3. Synchronization of an SDI studio . 44 5.4. Decoding and re–encoding of PAL signals . 46 5.5. Cascaded PLLs (reclocking) . 47 5.6. SDI to PAL (Dser/A) converters . 47 European Broadcasting Union Case Postale 67, CH–1218 Grand–Saconnex (Geneva) Switzerland 5.7. PAL to SDI (A/Dser) converters . 48 5.8. Thermal considerations for digital equipment . 48 5.9. 75 / 50 W connectors for SDI . 49 5.10. SDI cables . 49 5.11. Passive loop–throughs and 75 W terminations . 49 5.12. Integration of measurement equipment in a digital studio . 49 Chapter 6 Test and measurement equipment. 51 6.1. Test signal generators . 51 6.2. SDI analyzer . 52 6.3. Test signals for the SDI . 53 6.4. Bit–error ratio (BER) measurements . 57 6.5. Electronic data handling (EDH) . 58 Reference data and Standards. 59 Reference data . 59 Standards and specifications . 90 Appendix A Jitter in the serial digital interface. 93 Appendix B Equalization and dynamic range in SDI receivers. 101 Appendix C Market survey of measurement equipment for digital video signals (June 1995). 105 Bibliography. 116 Acknowledgement This publication has been prepared by an Ad–hoc Group within the EBU Technical Committee. It has benefitted from the collective experience of specialists in many EBU Member–organizations. The EBU is grateful also to the following specialists from industry for their valuable contributions: Mr. Ken Ainsworth, Tektronix, USA Mr. David Fibush, Tektronix, USA Mr. Sigmar Grundwalt, Rohde & Schwarz, Germany Mr. Johann Safar, Panasonic, USA Mr. Peter Symes, Grass Valley Group, USA EBU – Measurements in digital component television studios tech 3283 Introduction This EBU technical document is a guide to the assessment of technical performance in television studios which are designed entirely on the basis of digital component technology, or which incorporate such technology for use in conjunction with analogue systems. Interfacing is an important consideration in such installations, and in view of the fact that in many cases signal characteristics can only be measured at the input and outputs of equipment, measurements on parallel and serial interfaces carrying 625–line digital component video signals at the 4:2:2 level are a prominent feature of this document. Measurements on ancillary data signals including, notably, audio signals conforming to the AES/EBU digital audio standard, are also dealt with in some detail. In contrast, the performance of individual types of equipment found in a modern digital component studio environment – digital video effects systems, mixers, etc. – is not considered in any depth, except to the extent that inadequate performance (or constraints such as signal delays imposed by the type of processing involved) may have a wider impact on the overall perfor- mance through a digital production chain. The general principles of performance measurement set out in this document are also applicable to the 4:4:4 configuration of digital component television signals. Whereas, at the 4:2:2 level, a single serial or parallel interface carries a wide–band luminance signal and two colour–difference signals of lower bandwidth, at the 4:4:4 level two interfaces are used together to carry a total of four wide–band signals. These may be red, green and blue primary signals, or luminance and two colour–difference signals; in either case, the fourth channel can be used for an additional wideband signal such as an associated key signal. The serial digital interface (SDI) can also be used to convey other forms of television signal such as 525–line 4:2:2 digital component video or digital PAL sampled at four times the colour subcarrier frequency. While much of the discussion in this document is relevant also to these signal formats, no specific reference is made to the corresponding parameter values. The document is for the use of engineers who need to carry out measurements on digital video and audio systems. Such measurements may be necessary for many reasons: planning and installation, acceptance testing, maintenance and the checking of signals during programme production or play–out. A number of different technologies are involved and it is not possible to treat each one in isolation. The serial digital interface (SDI), combining 4:2:2 component video, AES/EBU audio, time code, signalling etc. into a single data–stream at 270 Mbit/s is the most complex of a range of digital signal configurations found in the television production environment. The correct functioning of these systems requires that consideration be given to certain aspects of the analogue video and audio signals, the waveform parameters and logic levels of the digi- tal interface signal itself, and a number of peripheral aspects such as conversion between the analogue and digital domains, PAL encoding, etc. The formal characteristics of the signals and interfaces involved in digital television production are set out in a number of standards documents, which are reviewed in Chapter 1. These standards define the conversion of a video signal from its analogue form (PAL colour, RGB primaries or analogue components), and the characteris- tics of the corresponding digital signals, which must be adhered to if compatibility is to be assured. These signal standards and the parallel and serial interface formats represent the main emphasis of digital television technolo- gy today and, despite its relative complexity and sensitivity to external influences, the 270 Mbit/s serial digital interface is supported by all modern digital television equipment. 3 tech 3283 EBU – Measurements in digital component television studios Chapter 2 is concerned with measurements in the analogue domain, and the relationships between ana- logue signals and the digital representations carried through the parallel interface and the SDI. Although much of the content of this document is concerned with digital interface performance, it should not be overlooked that the overall performance of the programme chain will be less than optimal if, for example, an analogue source signal does not confom to the relevant specifications, an analogue–to–digital converter is mis–aligned, or the analogue display system is mal–functioning. Chapter 3 is concerned with the data conveyed through a digital production system: validity of the trans- mitted data, timing, etc., whilst Chapter 4 gives details of a range of measurement procedures covering the physical characteristics of both parallel and serial interfaces: waveforms, signal levels, jitter, for example. Chapter 5 is concerned more generally with the way in which the digital component interfaces fit into the working environment of the modern production area. Digital video interfaces employ very sophisticated data transmission techniques and require the use of specialized measurement instruments. Chapter 6 discusses the characteristics and features of suitable test instru- ments and test signals. The document includes a Reference data and Standards section giving all the principal technical parame- ters of the interfaces discussed in the document and a list of relevant standards documents. Finally, a number of Appendices give further background explanations on several important measurement concepts relating to the serial digital interface and test instruments for digital video signals. Important notes 1. In this document, the more common signal nomenclature Y/CB/CR is used to designate analogue component signals, instead of the E’Y, E’CB, E’CR nomenclature specified in the relevant standards, although in principle Y/CB/CR refers to the digital representations of analogue component signals. 2. The PAL system has been used in this document to represent composite analogue signals. Statements con- cerning composite PAL are basically applicable also to SECAM systems. 3. Digital component television systems covered by this document may use 8–bit or 10–bit representations of signal levels. Where information relates specifically to 10–bit representation, the values are enclosed in angle brackets, thus: <...>. 4. Descriptions of digital video systems require the use of several different number representations. All values in hexadecimal notation are indicated in the form: NNhex. Decimal numbers are shown with the subscript NNdec only where necessary to avoid ambiguity. 5. The text includes cross–references