Danish company DK-Audio manufactures a range of metering products for both audio and video applications. The manufacturer is best known within broadcast and recording studio circles for its MSD range of audio meters, which incorporate a distinctive Jelly-Fish display for 5.1 surround sound metering. On the video side, it is now responsible for the manufacture, future development, and sales and marketing of the PTV range of products after acquiring the group (formerly part of Philips Television) in 2001.
DK-Audio’s PT5230 digital video generator features multiformat capability and a moving element in the test pattern.
Soon after the acquisition, TDC Tele Denmark approached the manufacturer with a request to develop a test card and sync generator that could incorporate a moving version of its logo. The network operator runs a switched video contribution network in Denmark, serving the needs of all of the country’s major broadcasters, including TV2, Danish Radio (DR TV) and TV3. The network is based on compressed video, using the ETSI algorithm. From the outset, the service provider realized that video compression equipment such as ETSI and MPEG contained framestores and, as a result, the still pictures its original test card equipment was generating were not helpful when it came to testing the transmission path. What was needed was a test card with a moving element so that its engineers at the receiving end could tell whether or not the signal had frozen.
In a contribution network, test cards are transmitted before and after the actual exchange of program material. This practice developed back in analog days out of an original need to check the proper alignment of the connection in the short (free of charge) period immediately before handover of the line to the broadcaster.
The test card was inserted at the sending end and the signal observed on a screen at the receiving point. The name of the carrier was inserted to help identify the source of the signals, thus making it simpler to locate a fault. Soon simple identifiers were replaced by logos, as it became important to the organizations involved to brand themselves.
As TDC’s logo passes through the RED field on the test pattern (located just below it), it synchronizes with a “click” in the left audio channel. If it doesn’t, then the audio signal is not in synchronization with the video signal.
Originally, the network operator was using an early PTV test card (PM5544, which in the UK is referred to as Test Card G) with a digital clock option installed. While this was successful in the analog world of yesteryear, it was not successful in the context of MPEG-2 or ETSI-encoded digital transmission because the changes from frame to frame were small and, therefore, difficult to detect. Initially, the company didn’t know how it was going to solve this problem. It had to be able to tell whether the signal had frozen, but the standard test pattern and sync generators that the company was producing didn’t measure up. They only produced the difficult-to-detect moving pulse rather than a moving logo or moving text, which the company felt would be much clearer.
PTV eventually agreed to develop a prototype solution, which at the time was based on the then recently released PT5210 test card. This incorporated the TDC logo, but because it was a prototype, it didn’t allow for any logo changes, should they be required. It did, however, add a moving logo to what had always been a still picture test card, thus enabling a much more critical test signal to be generated.
The network operator relied on the prototype for four years before DK-Audio agreed to build a production version of the PT5230 with moving logo and text generator. The operator was delighted when the digital video generator was announced because it needed at least five more, and it only had one prototype. One surprising benefit of the unit is that the test signal has become much more critical to the video encoder. By incorporating a moving logo, the network operator can now detect delays that might affect lip sync, something it is always anxious to avoid as even the slightest delay between sound and video is a sure way to spoil a viewer’s enjoyment of the programming. As the logo passes through the RED field on the test pattern (located just below it), it synchronizes with a “click” in the left audio channel. If it doesn’t, then the audio signal is not in synchronization with the video signal, and the operators can quickly do something to correct it.
Since the original prototype was developed, TDC’s network has expanded considerably, and thanks to a recent re-branding exercise, its logo has changed. The PT5230 has allowed the network operator to incorporate its new logo and has also delivered a moving logo without any of the compromises of the prototype solution.
The most obvious improvement is that the left audio channel “click” is now synchronous with the movement of the logo. Also, by incorporating the new logo, the service provider has been able to insert a well-defined test card, with accompanying sound, into the five nodes of its switched network. The combination of the fixed greyscale information above the moving logo and the information below (the yellow-red-yellow signal) is critical for MPEG coding and decoding. With the PT5230, precision is high and integration is simple as the interface is SDI video and embedded sound.
The proliferation of video compression in today’s television networks has made still picture test cards unsatisfactory. More and more broadcasters are requesting a test card with a moving element, whether that be a logo or just a simple line of moving text. As most transmission errors go largely unnoticed, a test card generator that delivers a moving logo is a vast improvement because transmission errors have a tendency to disturb the picture in the area around the moving logo, making them much easier to spot and to fix.
Eskild Nielsen is a senior engineer at TDC Tele Denmark.
