Primer A Guide to Standard and High-Definition Digital Video Measurements 3G, Dual Link and ANC Data Information A Guide to Standard and High-Definition Digital Video Measurements Primer Table of Contents In The Beginning . .1 Ancillary data . .55 Traditional television . .1 Video Measurements . .61 The “New” Digital Television . .2 Monitoring and measuring tools . .61 Monitoring digital and analog signal . .62 Numbers describing an analog world . .2 Assessment of video signal degradation . .62 Component digital video . .2 Video amplitude . .62 Moving Forward from Analog to Digital . .3 Signal amplitude . .63 The RGB component signal . .3 Frequency response . .65 Gamma correction . .4 Group delay . .65 Gamma correction is more than correction for Non-linear effects . .66 CRT response . .5 Differential gain . .67 Conversion of R'G'B' into luma and color difference . .5 Differential phase . .67 The Digital Video Interface . .7 Digital System Testing . .67 601 sampling . .9 Stress testing . .67 The parallel digital interface . .11 Cable-length stress testing . .67 The serial digital interface (SDI) . .12 SDI check field . .68 High-definition video builds on standard In-service testing . .68 definition principles . .14 Eye-pattern testing . .70 Jitter testing . .72 Timing and Synchronization . .17 SDI status display . .76 Analog video timing . .17 Cable-length measurements . .76 Horizontal timing . .18 Timing between video sources . .77 Vertical timing . .20 Intrachannel timing of component signals . .78 Analog high-definition component video parameters . .24 Waveform method . .78 Timing using the Tektronix Lightning display . .78 Digital Studio Scanning Formats . .25 Bowtie method . .79 Segmented frame production formats . .25 Operating a Digital Television System . .81 Digital Studio Synchronization and Timing . .27 RGB and color-difference waveforms . .81 Telecine synchronization . .30 Component gain balance . .81 The vector display . .81 Dual link and 3G . .31 The Lightning display . .83 Digital Audio . .45 The Diamond display . .84 Embedded audio in component digital video . .46 The Arrowhead display . .85 Extended embedded audio . .47 How to Monitor Gamut . .86 Systemizing AES/EBU audio . .48 Basic HD embedded audio . .49 Definition of Limits . .88 Audio control packet . .51 Conclusion . .89 How to monitor multi-channel audio . .52 Audio channels in 5.1 surround sound . .52 The surround sound display . .53 www.tektronix.com/video_audio i A Guide to Standard and High-Definition Digital Video Measurements Primer Appendix A – Color and Colorimetry . .90 Appendix D – Reference Standards and White . .91 Practices for Television . .99 Red, green, and blue components . .91 Appendix E – Bibliography . .100 Gamut, legal, valid . .94 Format conversion tables . .96 Appendix F – Glossary . .101 Acknowledgements . .107 Appendix B – Television Clock Relationships . .97 About the authors . .107 Appendix C – Standard Definition Analog Disclaimer . .107 Composite Video Parameters . .98 ii www.tektronix.com/video_audio A Guide to Standard and High-Definition Digital Video Measurements Primer In The Beginning television builds on what we already know about analog television. Light into the camera lens and sound into the microphone, are It is tempting to think of digital television as something very still analog. Light from the display and sound to your ears are scientific and even complex. But when we view the end result, still analog phenomena. we find something very familiar; something television engineers We already know that analog video is a “sampling” of light values. have sought since the very beginning… an experience that just Values of brightness represented by a voltage. And additional keeps getting better and better… quality video and audio information provides the color of the samples. The samples are conveying the artist’s performance to the viewing audience. synchronized through the transmission system to reproduce an The only thing new in digital television is the way the message image of the original scene on our display. Analog video travels gets from here to there. as a “serial” stream of voltage values containing all of the “data” Does it really matter how the message travels? The artist and necessary to make a picture when the receiver knows what to the viewer (and in many countries, the advertiser) probably don’t do with the information. So you can see that by just substituting care what path the signal takes. They can benefit from digital a few words, and by just doing a few things differently to take television’s improved performance without knowing the details. advantage of what we have learned over the past fifty years, Ah, but the science…. that’s where the fun comes in. Those of we can understand that digital video is really not very different us involved in the technical side of television do care; and we do than analog video. benefit from the significant advances in television science over So if we start with analog light and end with analog light, why the past 60+ years… and in particular the advances brought use digital video at all? In many cases, the camera sensor is about by digital television over the past 20 years. still producing analog video, but it is now common to almost Program video, digital audio, and associated ancillary data signals immediately convert the varying analog voltage representing the together make up the digital television signal. In the analog world instantaneous value of video to digital for handling with essentially of television, video and audio can exist in totally separate paths no degradation. In some cases, such as computer-generated video from source to the home television receiver. Digital signals may be or graphics, the video will start out in digital format, and with the organized with much more freedom, with video, audio, and other new digital television systems, it can reach the display never going signals working together as a stream of data. All we need to know to analog. is how the data is organized to pick out what we want. We can still send and receive television signals via analog NTSC, Traditional television PAL, or SECAM transmissions, but we are already using digital transmissions to convey higher quality, more efficient television We can call analog video and analog audio the elements of signals to the home. Digital television is an available part of traditional television. But it is important to realize we are still trying everyday life. Some of us will use it and contribute to its to accomplish the traditional goals… and maybe more. Digital improvement. Some of us will take advantage of it without television builds on analog, and our understanding of digital needing to know the details. www.tektronix.com/video_audio 1 A Guide to Standard and High-Definition Digital Video Measurements Primer The “New” Digital Television Component digital video The designers of early analog special effects equipment recognized Digital signals have been a part of television for many years, at the advantage of keeping the red, green, and blue video channels first buried inside equipment such as test signal and character separate as much as possible during any processing. The NTSC generators; later throughout entire systems. In this primer, we will and PAL encoding/decoding process is not transparent and multiple deal first with the video portion of the television signal for simplicity. generations of encoding and decoding progressively degrade the Audio will be digital as well, and will take its place in the digital data signal. The signal in the camera starts out with independent stream for recovery at the television receiver. Digital audio will be channels of red, green, and blue information, and it is best to discussed in later chapters. handle these signals through the system with as few format Digital video is a simple extension of analog video. Once we generations as possible before encoding them into NTSC or understand analog video, it is easy to understand how digital video PAL for transmission to the home. But handling three separate is created, handled, processed, and converted to and from analog. coordinated channels of information through the television plant Analog and digital video have many of the same constraints, and presents logistic and reliability problems. From a practical many of the problems that may occur in the digital domain are a standpoint, these three signals should all coexist on one wire, result of incorrect analog source video. Therefore, it is important to or commonly a single coaxial cable. As it turns out, we can have standards to reference for the design and operation of both simply matrix these three components, the red, green, and blue analog and digital video devices. video channels, to a more efficient set consisting of luma and two color-difference signals; digitize each of them, and multiplex the Numbers describing an analog world data onto a single coaxial cable. We can handle this data signal Early digital video was merely a digital description of the analog much as we do traditional NTSC or PAL composite video. Now we NTSC or PAL composite analog video signal. Standards were are handling a high-speed stream of numeric data. Although this written to describe operating limits and specify the number data signal contains energy changing at a much faster rate than data describing each voltage level and how each number was the 5 to 6 MHz energy in an NTSC or PAL video signal, it can be generated and recovered. Because of the high speed of the data, handled losslessly and with less maintenance over reasonable it was common to handle digital video data internally on an eight- distances. Once the video signal is in the digital domain, we can or ten-bit bus, and initial standards described a multi-wire external easily extract its components for individual processing and connection as well. The standards also described certain ancillary recombine them again in the digital domain without any further and housekeeping data to synchronize the receiver and the loss or interaction among the channels.