Test and Measurement Advances to DTV

Multifunction monitors tackle MPEG, ATSC
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Multifunction monitors tackle MPEG, ATSC

NEW YORK

Whatever else can be said about the ongoing DTV transition, it has stimulated the development of a new generation of test and measurement equipment for the video, audio and broadcast community.

Obvious among new offerings are all sorts of MPEG analyzers - from laboratory models used in the development of encoders and set-top boxes to units designed for a TV station's everyday use to check all pathways of the compressed signal chain, from ingested materials on an MPEG server to the final ATSC transport streams.

But the equipment that performs the bread-and-butter measurements such as video waveform and vector, audio level and phasescope, is transforming as well, from single-function, instrument-grade CRT type units to multifunction, multiformat, multidisplay, network-capable analyzers that can use external computer VGA or regular video monitors, or attached TFT screens.

ANALOG VIDEO

Recognizing that broadcasters are making significant financial investments in DTV equipment and services, manufacturers of test and measurement equipment are designing cost-effective and feature-laden products that will serve not only broadcasters' current needs, but ongoing and future requirements as well.

"Broadcasters know they have to replace equipment now while they are still in the analog world, but in the future they will be heading into the digital world," observed Greg Huttie, director of product development, Videotek Inc. "They want test equipment to be able to handle both analog and digital, to be useful now and useful in the future, so they don't have to spend the money twice."

Videotek is addressing this need with the introduction of a lower-cost unit in its VTM series of quad-display test gear, the VTM-150. "The VTM-150 has the ability to do analog and digital, waveform and vector displays that can be keyed over picture or displayed by themselves, all at the same time," Huttie said. "Stereo analog audio is also included."

The electronics of the VTM-150 are in a 1 RU frame connected to an external VGA monitor.

On the transmission side, existing analog transmitters have to be maintained and operated in compliance, even as digital transmitters are put into service.

"While the glitter may be digital, what pays the bills is the analog transmitter," said Chuck Barrows, vice president of Marketing and Sales for Magni Systems Inc. "But with the emphasis on digital transition, some companies are dropping equipment for analog transmitter measurements like ICPM [incidental carrier-phase modulation], leaving room for us at Magni to fill this niche."

Magni's AVM-510A-T provides analog transmitter measurements including ICPM, differential gain (DG) and differential phase (DP) along with its other rasterized waveform and vectorscope measurements. Magni makes use of an external video monitor to display these screens.

DIGITAL VIDEO

Even if a station has converted its baseband system to digital, life doesn't necessarily get simpler. Digital comes in many formats. News may be done in some standard definition (SD), while production may be in some form of high definition (HD). Multiple SD feeds may be transmitted at some times of the day, with a single HD program stream offered during primetime.

That's why flexibility and versatility are important in the design of digital test and measurement equipment.

For example, the LV-5700, made by Leader Instruments Group, can handle 20 digital formats and auto-detect between HD and SD, said Joe Fisher, product marketing manage at Leader.

Test and measurement equipment manufacturers say that due to customer demand, the growing trend is for displays to show several aspects of a signal simultaneously.

The LV 5700 is a 3 RU unit that fits in a standard half-rack-width frame and employs an integral XGA TFT screen, that can be tilted. The screen can be segmented into quadrants, each displaying a different type of measurement, such as video waveform and vector, audio, status or a thumbnail video picture. New options include HD eye pattern and auto jitter.

Another example, the Videotek VTM-420HD/SD, automatically recognizes HD or SD in any format and measures picture, waveform, vector and audio on a single high-resolution XGA monitor and includes 601 processing and closed-caption monitoring.

AUDIO

Audio in the digital transition also comes in a variety of flavors. Analog is still prevalent even as the conversion to AES/EBU digital continues. And the big-ticket item, Surround Sound, also known as 5.1 audio, is making inroads, significantly in production and post production.

The DK-Audio MSD-600M series offers a variety of modules that can be changed as user needs warrant.

"As users migrate from analog to AES, or add embedded audio, they use the same gear, but just change cards in the back of the unit," said John D. Terrey, vice president of DK-Audio America Inc.

To help visualize the Surround field, "DK-Audio employs our unique trademarked jellyfish pattern that graphically represents the sound intensity of the Surround space and indicates if any portion is out of phase," Terrey said.

The MSD-600M series also includes a test generator for such signals as white and pink noise, an FFT analyzer, one-third octave analyzer and out-of-phase analysis by timecode.

Many analyzers are now measuring audio as well as video. The Videotek VTM-420HD/SD has its own CineSound display for 5.1- or 7.1-channel audio, a Lissajous pattern for audio phase, up to eight channels of bargraphs and analog, AES/EBU and embedded inputs plus a new option for Dolby AC-3 and Dolby E encoded audio.

The Leader LV 5700 takes in embedded audio, decodes it and displays it as 3:1, 3:2 or 3:2:2 Surround images, multi-Lissajous or eight-channel bargraphs.

The Magni SDM-560M includes audio metering and phase displays of embedded SDI, AES or four-channel analog.

MPEG

The transition to digital inevitably ends up as a transition to MPEG, if nowhere else than the ATSC transport stream mandated for U.S. DTV.

Triveni Digital's StreamScope real-time ATSC transport stream monitor and analyzer is used during all phases of the DTV transition, said Nandhu Nandhakumar, Triveni vice president of engineering and chief technology officer.

StreamScope provides visualization of data to help users better comprehend how a system is operating.

The "packet map" display, for example, shows each type of packet, such as video, audio, data or PSIP as a different color. Clicking on individual packets provides a display of each packet's full content such as ID and payload, which are described using semantic labels.

StreamScope also provides PCR timing, video and audio buffer analysis and graphing plus cross-table consistency analysis, comparing contents of PSIP and MPEG-2 SI (system information) tables.

Another example of ATSC transport stream monitoring is the Pixelmetrix DVStation, for which an 8-VSB interface was introduced at NAB2002.

According to Pixelmetrix, "the interface allows DVStation to measure 8-VSB modulation quality, monitor the MPEG-2 transport stream and validate program content. A graphical display uses color coding to highlight actual constellation, pilot and data carrier points."

Rohde & Schwarz offers products in all global standards, said Marketing Manager Rudy Niznansky, "and is very active in continued improvements to its ATSC measurement equipment products."

The 8-VSB Rohde & Schwarz EFA-52 precision demodulator "measures the RF quality of a station's digital broadcast stream," Niznansky said. With the DVRM, "the demodulated MPEG-2 transport stream can be continually monitored for ETA-290 compliance, and picture quality can be quantified by using the DVQ."

As the digital transition progresses, it's inevitable that interoperability issues will crop up. Tektronix has been called in recently to help arbitrate a few cases between encoder and set-top box manufacturers to solve the mystery of why closed captioning wasn't being displayed properly.

Tektronix evaluated a recording or sample of the disputed stream using its AD953 MPEG Test System with the IN option that allows drilling down from the transport stream to the elementary stream.

"That way we can look into individual packets that make up individual programs to look at the data to see if closed captioning is really there," Tucker said.

In one case, Tektronix MPEG Application Engineer Dennis Kucera reported that of the eight sets of closed captioning and text in one transport stream, one was found to be in error. "The set-top handles the errors differently, but the result is that it doesn't look right on air," Kucera said.

Tucker believes that closed captioning will become a major issue through the digital transition and that "broadcasters will need the right equipment to ensure that closed captioning is encoded correctly."

CENTRALIZED AND REMOTE MONITORING

Just as digital technology and automation systems provide the means for the operation and control of many TV stations from a single central location, so too has SNMP and IT technology allowed test and measurement equipment to be networked.

Systems can meter and monitor video and audio equipment within a single facility from a central point within that facility, typically the chief engineer's PC; or, analyzers positioned in number of facilities can be networked over LANs, allowing central monitoring from one geographical location.

When out-of-tolerance conditions are met, the systems can send out alarms to perform any number of tasks - from lighting a red warning light in a studio to recording the corrupted signal to waking up the chief engineer at two in the morning.

"This is huge," Huttie said. "This is where the industry is going."