The broadcast industry continues to move ahead with new technology deployments for DTV at a rapid pace — from mobile DTV to 3-D TV (the latter certainly being the biggest buzz in 2010). It is challenging enough for broadcasters to keep up with these new technologies from an installation and operational standpoint. Adding to this challenge is the test and measurement aspect to confirm that such technologies are operating as they should and without detriment to the quality of broadcast and/or production.
Some of these technologies will require new equipment to measure and ensure compliance with technical standards. When data rates (adoption of 3Gb/s) or physical formats (like optical interfaces) change, there is no choice but to upgrade test equipment. In this situation, specialized tools such as physical layer testing of 3Gb/s signals are required.
Many new technologies, such as stereoscopic 3-D, can be measured with the current generation of test equipment using some common sense and an understanding of the new technology. This article will detail some methods of testing new and existing technologies with techniques using common video test and measurement equipment.
-D TV measurements
Those who attended the 2010 NAB Show this spring can confirm that 3-D TV has evolved from early development to limited commercial deployment in a relatively short time. As of this summer, 3-D-capable TV sets are available for purchase, and cable and satellite services in the United States are carrying 3-D TV channels. While this is an intriguing proposition for consumers (and an attractive business opportunity for consumer TV set manufacturers), it has forced production, edit and broadcast facilities to quickly implement 3-D production. This creates an immediate requirement for 3-D TV signal test and measurement, and there is a clear and definite learning curve.
3-D TV measurements focus on the differences between left- and right-eye signals. There are three basic qualities to focus on when recording measurements between left- and right-eye signals: timing differences (at the transport level), amplitude and variances.
The measurement of timing differences at the transport level (i.e., horizontal and vertical timing reference signals) is straightforward. Modern test equipment often has built-in functions to measure this type of timing difference. Such functions include the ability to measure a video input signal relative to another video input, time code and analog timing reference signals.
For 3-D camera setup, the operator needs to determine whether the “dual camera rig” is physically positioned in a manner so both the left- and right-eye cameras' field of view precisely overlay each other. The operator also needs to verify that the camera images' geometry, gain and color balance parameters have been adjusted such that both images match each other perfectly. And most importantly, the camera operator needs to be certain that the 3-D disparity of the camera is adjusted per the requirements of the program.
Figure 1 demonstrates a quadrant display useful in camera setup. Here, the operator can view the left-right monochrome image to determine whether the cameras' geometry is correct; it further demonstrates the disparity between the left- and right-eye images. The checkerboard display allows the video operator to match the colorimetry of the camera setup; the 3-D waveform is useful is determining the disparity of the scene; and the anaglyph allows the operator to view the scene in 3-D on a standard monitor. Any of the four images can be viewed full screen to examine details as required by the operator.
The measurement of amplitude difference between left- and right-eye signals is equally straightforward. There are a few different ways to accomplish this task. The most direct method involves an overlay of the left- and right-eye waveforms. This allows direct observation of amplitude (and to a lesser degree timing) differences. The test equipment aids in the comparison by showing each input in a different color, which makes it easier to differentiate the left- and right-eye signals. This overlay technique is also an effective way to compare the left and right vector display.
A combination waveform/vector display is another method of displaying timing and amplitude differences. This is an ideal choice when there is a requirement to display more information simultaneously. The combined display shows left- and right-eye waveforms and vectors side by side.
Thumbnail picture displays can also be viewed in this configuration to allow simultaneous monitoring of six different signal elements (left- and right-eye waveforms, left- and right-eye vectors, and left- and right-eye thumbnail pictures). These identify the variances of left- and right-eye signals with more clarity.
Embedded audio is the most commonly used form of ancillary data within an HD video signal, and there are some embedded audio measurements that can be made using general-purpose test equipment.
One of the most common questions when using embedded audio is also one of the most basic: “Is it present?” Fortunately, there is a straightforward method of detecting embedded audio presence by direct observation. Using the horizontal and vertical delay settings (“pulse cross”) of the picture display allows for direct observation of the horizontal and vertical blanking areas of the signal. Embedded audio has a specific pattern when viewed this way: It occupies a certain portion of the horizontal blanking region; it is not inserted in a certain portion of the vertical blanking region; and it is evenly distributed. (See Figure 2.)
There are other embedded audio issues to evaluate besides presence, including the embedded audio type (basic AES or Dolby-encoded). If Dolby-encoded, is the timing relative to video correct? Advanced test and measurement tools exist to answer these questions.
A tool that can display and analyze data values within a video signal can yield more information about embedded audio. A search for the SMPTE data identifier values using an appropriate data analysis tool can instantly find the embedded audio data. An additional search for the Dolby header values will determine whether the embedded audio is Dolby-encoded. If so, it is a simple matter to view the position of the Dolby header value relative to video to determine whether it is properly positioned.
Other ancillary data
Some of the embedded audio analysis techniques described above can also be applied to other ancillary data types. The use of the picture display function along with pulse cross will obviously show all embedded data, not just embedded audio. While the data will be present and visible, identifying other (as in nonembedded audio) data types can be a challenging task. One data identifier looks just like another to the human eye.
The data analyzer tool is helpful for this application. These tools can at a minimum show the actual data value, typically in hexadecimal. An ancillary data packet can be identified manually by finding an ancillary data header, such as the sequence of 000 3FF 3FF (hexadecimal) that only appears at the start of ancillary data. (Some data analyzer tools can automate this search.) The data analyzer tool can subsequently identify both the data identifier value and the data packet content. (See Figure 3.)
A simpler way of verifying many types of ancillary data is by decoding and viewing the data. Most modern test and measurement equipment can decode and display certain ancillary data. A partial list of these data types includes closed-captioning, teletext and OP-47 subtitles. Other ancillary data types, such as AFD data, can be detected and displayed in a simple human-readable form. Obviously this type of display and monitoring at a higher level is simpler than using the data analyzer functionality.
Test and measurement techniques are constantly changing to keep up with new technologies; however, this does not mean that every new technological introduction requires a new generation of test equipment. Many new broadcast technologies can be monitored with existing equipment using common-sense applications.
Dave Guerrero is vice president and general manager of Videotek for Harris Broadcast Communications.
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