Test and Measurement Breakthroughs for DTV
Compared to NTSC, DTV broadcasting requires many more devices for test and measurement. Besides conventional waveform monitors and vectorscopes for monitoring video quality, broadcasters also need devices that will analyze the transport stream – with its digital packets of MPEG video, AC-3 audio, PSIP and other information – as well as the 8-VSB RF modulation from the DTV transmitter.
Because of the complexity of the DTV process, vendors of test and measurement equipment use very precise language to describe the specific problem or function their device can monitor.
"You have to be careful with words like ‘analyze’ and ‘bitstream’ because these words cover a lot of territory, and can be confusing or misleading," says Eric Small, chief technical officer for Modulation Sciences in Somerset, N.J.
"When our DTV adaptor for the msi-320 Precision Video Demodulator becomes available, it will analyze the 8-VSB signal. It provides an eye-pattern and statistics on the operation of the 8-VSB process. Our DTV msi-320 will look at the product of the 8-VSB modulator, and analyze the RF signal to determine how good a job the DTV transmitter is doing. This information is valuable to engineers, especially in setting up the transmitter," says Small.
Recognizing that DTV broadcasters need a varied toolbox of test and measurement systems, Small adds that the msi-320 will be extremely cost-effective. The current analog NTSC unit costs one-sixth as much as the leading competitor’s product, and the DTV msi-320 will also save money without sacrificing precision monitoring.
JUMPING INTO THE BITSTREAM
"If you’re doing datacasting, or if you want to evaluate MPEG video in the ATSC transport stream, you need a device like Triveni’s MT-20 StreamScope, which can break out the individual signals from the multiplex and evaluate them," says Joe Fisher, product marketing manager for Leader Instruments Corp. in Cypress, Calif.
Besides its own portfolio of test and measurement products, Leader also reps the MT-20 StreamScope for Triveni Digital, a DTV engineering firm in Princeton Junction, N.J. A real-time ATSC Transport Stream Monitor and Analyzer, StreamScope lets broadcasters monitor, record, and troubleshoot crucial properties of an ATSC DTV broadcast stream – including ATSC, MPEG-2, and PSIP Program Guide compliance - and display and analyze that data with an innovative, easy-to-use graphical interface.
"With an 8-VSB card, the Triveni system can also monitor off-air signals to check for compliance. Cards are now available for ADI and SMPTE-310M," adds Fisher. "But, within the studio, engineers can use our new LV 5170D to check the integrity of SD and HD signals from cameras and tape decks."
The LV 5170D is a Multi-Format HD-SDI and HD-Analog device that performs auto detection, setup, and display of 14 HD-SDI, formats, including 720p, 1080i, and 1035i. It analyzes and displays waveform, vector, picture, audio and hex data.
"Unlike competing devices which use VGA-rasterized displays, the LV 5170D uses two true instrument-grade CRTs that analyze the HD signal’s full 30 MHz bandwidth," says Fisher. "While a rasterized display shows 640 by 480 (or 300,000) pixels, which is only 15 percent of a full HD frame, our product provides full analog HD (1920 by 1080) for monitoring all 2 million pixels; plus our CRTs provide true clarity that HD camera operators, editors, and colorists prefer for a more credible signal evaluation."
TAKING A DRIVING TEST
"The biggest challenge in DTV today is reception, and ensuring that your DTV signal has the same footprint as your analog signal," says Jason Somera, spokesman for Z Technology in Beaverton, Ore. "DTV broadcasters need a way to verify their DTV signal coverage and identify problems such as signal nulls due to reflections and areas shielded by terrain or buildings."
To enable "drive tests" to determine signal reception throughout the TV coverage area, Z Technology offers the DSS5800 Windows-based RF field- strength and digital-parameter mapping system. While users drive, this portable, turnkey system – including laptop, DTV tuner, FCC-calibrated tuned Dipole Antenna, and programmable field strength meter – automatically collects data (such as peak signal power, integrated power, band pass tilt, signal notches, and standard deviation) for up to 50 digital or analog TV signals simultaneously and displays color-coded results on digital street maps bundled with Z’s Drive Test Analysis software.
"When viewers report reception problems, this portable system can even be taken inside their homes to determine the best location for their antenna," adds Somera. "This unique system has been purchased by ABC, Tribune, and Cox stations groups. However, 50 percent of our market is related to DTV Datacasting, with sales to datacasting vendors like iBlast, Dotcast, and Clear Channel."
WE’RE THE MPEG GENERATION
Since MPEG-2 is the foundation of the ATSC video standard, DTV broadcasters have been investing in a wide range of MPEG systems, including encoders, decoders, and servers. Even though video has been compressed into MPEG-2 files, the pictures still need to be tested and evaluated for quality control.
With its MosaLina MPEG-2 Software Analyzer, U.K.-based Snell and Wilcox, emulating the conventional frame-by-frame "naked eye" method, provides MPEG-2 users with a repeatable and reliable means of assessing both SD (MP@ML, 4:2:2P@ML) and HD (MP@HL) picture compression quality. Priced below $5,000, this Windows-based software offers a scalable, affordable way for compressed material to be batch- captured and quantitatively checked against standards so that problems can be spotted quickly.
"Because of its affordability, broadcasters can use MosaLina daily, in multiple locations, for off-line analysis of picture quality of MPEG-compressed files, faster than real-time," says John W. Shike, vice president of marketing for Snell and Wilcox U.S. office in Santa Clara, Calif. Also, with companion product MosaLina Expert, transport and program de-multiplexing is possible for assessment of complex bitstream structures.
PREVENTIVE MONITORING
Pixelmetrix is shipping its new DVStation, a self-contained, end-to-end "Preventative Monitoring" system designed to continuously analyze the performance of digital broadcast networks. "DVStation can monitor thousands of parameters within hundreds of DTV signals simultaneously, in real time, and from a single, self-contained device," said Danny Wilson, president of Pixelmetrix. If a preset threshold in the broadcast signal moves out of range, DVStation can send a warning before system failure brings the network down. If a service parameter in a program - such as language or subtitles - becomes mis-configured, DVStation’s On-Air Service Content Validation alerts operators. DVStation is so user-friendly, said Wilson, that a non-technical operator can monitor its complex analysis through simple "red light, green light" alerts. Problems can be isolated quickly because DVStation generates a comprehensive log that clearly explains which system threshold deviated from the norm. DVStation is also highly flexible, offering such options as single location monitoring of several un-staffed remote sites and operation through a corporate LAN or over the Internet.
"The key idea is ‘Preventative Monitoring,’ a comprehensive strategy for ensuring optimal network performance by detecting and logging problems before a network failure can occur," Wilson said.
STEERING TOWARD AUDIENCE SATISFACTION
The Tektronix AD920, a hand-held, battery-powered MPEG transport stream confidence tester, reduces downtime, enables faster installation, and quickly identifies faults in MPEG-2 transport streams. It analyzes MPEG-2, DVB, and ATSC streams via SMPTE 301M and ADI interfaces at up to 100 Mbps. It complements Tektronix’s ever-expanding portfolio, including WFM700 multi-standard, multi-format Modular Waveform Monitors - for measuring HD and SD digital signals in the same cost-effective, modular platform.
"The main compression issues faced by broadcasters will most likely be created by the re-multiplexing and re-generation of content," says Spyros Lazaris, worldwide marketing manager of the Video Business Unit of Tektronix, Inc. in Beaverton, Ore. "These issues might create timing and/or system information errors in the MPEG stream that can either lead directly to picture quality issues, or to other re-multiplexing errors downstream. Tektronix’s MPEG transport stream monitors allow broadcasters to protect against over-compression … which leads to an undesirable viewer experience."
Since MPEG compression can introduce picture defects, such as "blockiness," which might not be detected by waveform monitors, Tektronix also offers picture quality monitors. Lazaris adds, "Our products enable broadcasters to detect errors before they become customer complaints; manage their total costs by balancing the delivered picture quality with the related infrastructure costs; and lower their long-term cost of ownership of capital equipment."
