Evolving Test and Measurement


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Time and accuracy are vital when producing content for broadcast. All broadcasters have strict schedules to work to, as well as visual and audio standards that need to be met. Effective testing and measurement (T&M) of any material that is to be transmitted is key to ensuring these parameters are adhered to, for both producer and broadcaster; get these wrong, or trust in inadequate equipment, and it could be very costly.
Broadcasters have invested huge sums in upgrading infrastructures to offer audiences the best quality television, so they must have programming to the highest possible audio and visual standard. If they do not, it is not only a waste of the upgraded infrastructure, but it is likely to have an adverse effect with viewers as well as advertisers, who will both be dissatisfied with the quality and may well end up abandoning the broadcaster.
To ensure their content is up to scratch, producers need to perform a range of T&M procedures. In terms of vision, this means checking synchronisation, levels, timing, distortion and colour gamut. The latest developments in broadcast stereoscopic 3D (S3D) means that this now needs to be checked with great accuracy. Although this is still somewhat a niche market, it is an important one, with some broadcasters and viewers alike investing large sums into S3D equipment. Such accuracy is needed to ensure that the two cameras needed to produce the S3D effect are aligned exactly. If they are not, it can cause viewers to experience headaches and nausea, as their eyes are sending the brain a different message to what it is expecting. While there are sophisticated tools to help the producer achieve accurate matching between the two images, we do not yet fully understand what makes compelling S3D and perhaps more importantly what makes it comfortable to watch.
Furthermore, while the movie industry has invested millions into creating S3D content, which is mostly checked in post-production, this model will not transfer to the broadcasting industry. Not only are budgets infinitely tighter, the greatest potential for S3D is live sport, where altering the picture after the event is not possible. Therefore any T&M, and consequent corrections, need to happen during the capture of the images. This is complicated when you consider that the distance between the two cameras capturing these images needs to change depending on whether it is a close up or a wide-angled shot.
Another important check to make is for anything that could trigger photosensitive epilepsy, otherwise known as PSE, which affects about one in every 5,000 people. Flashing lights or certain colour combinations can cause PSE sufferers to have an epileptic episode, which can create great distress for the person concerned, as well as those around them. Fortunately, over the years, we have learnt a lot about the causes of PSE, and broadcast engineers have been working together with doctors to develop algorithms to detect potentially harmful sequences and remove them before transmission. There is also an internationally agreed standard, ITU recommendation 1702, that any producer or broadcaster concerned about PSE should make sure is included in their T&M equipment.
The test for PSE and its correction is done automatically, which is what will ultimately happen with all quality tests, both sound and vision. Although we are part of the way there, there is still some way to go. Several years ago, T&M required a skilled engineer sitting in front of a variety of different screens and standalone devices. This has proven to be a very costly procedure for producers, who not only have to pay for the equipment but also need to employ or hire a number of specialists to operate it. They must also commit large amounts of valuable space to storage and ensure that it is all maintained and operating as it should. However, thanks to pioneers such as Hamlet, this no longer needs to be the case, with many of the common tests being consolidated into single devices. Indeed, there are now software solutions that enable T&M to be conducted on an engineer’s own computer to make life even easier.
Having invested in a 3D or HD television, viewers not only expect the best possible picture, but also the best possible sound. In the past this was something that producers did not have to worry about as a majority of their audiences would be listening to content through paper speakers on the back of their CRT sets. But as sound systems have become more sophisticated, so has the viewers’ perception of broadcast sound. As such, producers need to ensure that levels are consistent throughout content and are not loud enough to cause distortion or quiet enough to be noisy. However, level metering is not ideal for measuring the actual perceived loudness, which depends upon the content and duration of sounds. This is now being recognised by broadcasters and international bodies, which have finally taken action, developing an accurate means of measuring perceived loudness, and drawing up specifications. Everyone is more or less agreed that ITU recommendations 1770 and 1771 are the world standard.
In stereo, the phase of the output needs to be checked, which is even more important for surround sound. Substantial out of phase audio makes audiences feel uncomfortable at the best of times and physically sick at worst. Channel separation and balance also need to be monitored.
So, as can be seen there is much to be tested if overall quality is to be assured, but what to test it on? Producers need to ensure that they meet several requirements if they are to offer a great return on investment. Accuracy undoubtedly needs to be a top priority. If T&M equipment is producing inaccurate results, then any changes that are made as a consequence are also likely to be wrong, and could make matters worse.
As we are talking about test AND measurement equipment, the most cost effective devices are those that can both generate the test signal as well as measure the results. Additionally, it needs the flexibility to be able to measure what is most appropriate for the particular application. While this sounds as though the equipment needs to be large and unwieldy to include these elements, T&M devices must be small enough to be able to be kept in production areas as well as be intuitive to use and produce results that do not need a specialist engineer to interpret. Finally, this should all be affordable for broadcasters and producers to check signals every time there is a process that could cause signal degradation.
With all this in mind, producers need to consider if their existing test and measurement equipment meets the grade, needs to be calibrated, or if they need to get advice and revise their T&M requirements entirely.

Tags: iss067 | test and measurement | s3d | pse | itu 1770 | itu 1771 | N/A
Contributing Author N/A

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