The importance of analog monitoring

For those of us who have been in the TV business for some time, there's one especially frustrating experience: seeing a aged product. A couple of months ago I came across a midnight repetition of a certain product that I helped perpetrate in the eighties and whose name I do not want to remember. And although at the time the superspecial in question swept with awards and favorable reviews, I had to dress in honesty and accept that by today's technical standards the product it's just lousy. The dramaturgy is solid, the (almost) impeccable assembly, the artwork simply sublime and the decent sound but the picture is horrible.

I talked to my colleagues from that time and we arrived. to the same conclusion: the truth is that we could have done it better. By those years we had not learned to handle the truculent relationships between aesthetic requirements and video limitations. And to achieve the look that the product required we opted to ignore the old monitor of waveform that accompanied us.

The result was an 88-minute piece with the blacks. completely crushed, whose prospects of reuse in the digital world are null. And that's not just a technical problem: it is a commercial matter. Afternoon or early the historical value of the piece will generate ideas of relaunch and someone is going to speak very badly of those who we were out there.

Monitor or not monitor

I know very successful television operations that have taken the preset option: everything is issued as it arrives. Is frequent noise in news broadcasts in the audio because the video is saturated, or that the inconsistencies in audio levels generate variations unpleasant in the loudness of the emitted signal. And when it is takes the option to process the material for aesthetic purposes is usually incurs excesses: sufficient levels of chrominance to generate losses of vertical synchronism, or excesses in the audio equalization capable of completely eliminating the intelligibility of voices.

Very well. Over time I learned my lesson. I'm really sorry but I can't agree with that attitude towards management audio and video signal technician. I am a firm believer in the value of traditional technical control processes. Reference displays and speakers, waveform monitors, vectorscopes, VU/PPM meters and audio phase monitors are friends of quality. And with time and notable improvements in the performance of video cameras, have ceased to be enemies of creativity.

Quality assurance of audio and video signals is not easy task. If we talk about composite video we should rigorously control luminance, chrominance, phase levels color (NTSC only), synchronism pulse integrity, three or four aspects of timing and making sure too, through a good screen, that we are delivering a decent image. And the audio can be even more demanding.

Why do we need to control all those boring ones? technical parameters? Simply to ensure that the Distribution of the material that has been delivered to us is successful.

Let's develop this idea a little. What do we gain by registering in tape a video signal so saturated that it generates sparks in the playback?, or raising the audio level to extremes they generate a constant distortion in the voices? Our systems distribution has limits, and the reason for controlling the Technical parameters of our signals is to ensure that these limits are not exceeded. That justifies the monitoring effort. technical: what is the point of engraving or airing material that the public will not see and hear correctly?

An additional note: many tend to believe that the use of digital channels and media makes these issues irrelevant, but let's remember that what in analog environments is distortion, in digital environments becomes clipping, in the total suppression of the incorrect signal which, in fact, is more notorious than analog saturation problems or pulse contamination.

I think at this point I can put a closure to the story of my product with crushed blacks. Thanks to what I have learned in recent years, I now know that in many regions of the country the public had to endure constant disturbances of vertical synchronism because we we arrange to generate a recorded signal with disturbances in the pedestal, completely unacceptable in an NTSC environment. Definitely, it would have been better to respect the monitor in a way wave.

From this point we will concentrate on the subject of video. The audio levels can be managed by a effort to adapt the dynamic range of the signals to each distribution channel, a topic we have covered in several opportunities in TV and Video.

Spaces and boundaries

There is an English name for the boundaries of a signal transport space, and this name is absolutely untranslatable. The word in question is gamut. For many, gamut is an absurd parameter that appears on waveform monitors and that we can ignore quietly because when the alarms go off they do not nothing happens.

When we start working with teams completely digital, we discovered delighted that the cameras allowed us handle more saturated colors without introducing obvious defects, and that recording media tolerated drastic increases in the level of our audio signals, with no apparent distortion.

What was going on? Well, while we were producing in a digital environment with a greater dynamic range in audio and video, our viewers kept watching us on their TVs always, using the same link-based transmission network analog composite video, compressed audio and with limitations of always in terms of modulation. But with the Time began to arrive the problems: those strong colors appear in the air accompanied by a dance of jumping points, and audio with increased dynamic range sounds as bad as your analog equivalent.

In essence, the problem is that the systems of production based on the CCIR-601/709 standard generates signals that have a greater range of colors than can handle the RGB or encoded video systems, defined by standards of color TV of the fifties and in many cases a direct conversion of material between the digital realm and the analog generates signals with values Illegal. It is possible that videotapes resist excesses, but air does not Sorry.

Now, what do the values of gamut that depend on? do you trigger alarms on our measuring equipment? Fundamentally of the procedures used to generate and transport color information, known as colour. For example, video cameras and computers Moderns use the same color space, based on the use of independent signals for the three basic colors of a optical color mixing, the famous RGB system.

The color variations that can be accommodated in the space RGB color are more than can be described in signals PAL or NTSC, which use an encoding model of color by the mathematical combination of signals of color difference, the famous components Y/Pb/Pr.

Why did you take the option to adopt a color space? new, when the native format of video cameras was RGB? Because of the need to maintain compatibility with the black and white TVs existing at the time of the arrival of color. Component color coding is more economical depending on the bandwidth used for transmission, but when it comes to emitting the signal or register it in the oldest recording systems, the signals undergo a further reduction in color space by becoming color-handling composite video using a model known as HSL (Hue/Saturation/Level) , which in some circumstances reduces the number of colors possible to less than 90,000.

Let's use a simple example to describe the consequences of the coexistence of different color spaces in our work environment. Cameras are RGB devices by definition, and usually make an internal conversion to a component video signal, which creates component video signal risks gamut errors. It is possible that some manufacturers try to legalize your signals, but for others fidelity is more important, even if signals are generated slightly outside of standard. In many cases we need to use video signals compound, which means an additional conversion and in numerous occasions an additional generation of gamut errors.

And let's remember that our dear viewers continue to watch our material on televisions based on composite video at best style of the 1950s. Which justifies all the technical monitoring efforts we make to adapt our products that TVs can play.

The truth is that taking measurements early in the ninety, when they coexisted in our production plants composite and component video equipment, we would have found a very high incidence of gamut errors generated by the direct conversion of signals. A well-known engineer Colombian says that his staff have been digital teams warmed eyes, referring to the widespread tendency to operate with higher chrominance levels, than although work perfectly on your cameras and monitors, they can have unpredictable effects on emission.

Let's pause to ask a question: do you think? that the incidence of errors of this type in our plants of Has production increased or decreased in recent years? Every once we work with teams that offer one more gamut and we attach less and less importance to control technical, I would say that this gives to think a little.

The price of digitalization

The color space variations we come from speaking are characteristics of analog systems of production. When systems begin to appear completely digital standards based on CCIR-601 or CCIR-709 standards equivalent for HD environments gamut inconsistencies they tend to get worse.

Ccir color space includes and exceeds gamut characteristic of the RGB/YUV/HSL color models used in the television industry. This implies that computers based in 601/709 patterns always have the potential to generate illegal signals in the other environments. And this potential tends to be realized when production systems are digitized totally and it becomes more difficult to locate the possible errors of gamut.

Some operations implement practices engineering that address the gamut problem from the production, trying to get staff to use settings that allow to generate valid signals of encoded video. And sometimes on-the-fly adjustments of signal levels that do not give optimal results, but are better than nothing.

Finally, in some cases processes of legalization of signals in the transmission chain, which it makes sense thinking that the material produced in the Present could be reused when the transmission is digitize and effectively start broadcasting in spaces of color very close to those established by the CCIR standards.

But the truth is that in many operations of television this issue is simply not discussed, and this attitude generates less than ideal conditions for users of our analogue transmission networks, which, by Obvious reasons, they will not be subject to major improvements since this time until its final blackout in the coming years.

Paradoxically, by ignoring the limits of the coded signals and current modulation systems, we are demanding more than ever from our networks, and punishing viewers increasingly demanding and also equipped with screens that allow for more critical performance evaluations of our transmission operations.

It is inevitable that our SD signals will not look very good when scale them on a flat screen with HD resolution, and I think it is a fact that the analog noise generated by gamut errors it will not help the viewer feel happy in a scenario like that, especially when you can appreciate the difference in quality with the signal that a player gives you $25 DVD-Video connected by components.

Let us also remember that we are in direct competition with Pay-TV operations with frontline equipment and personnel, and that the ordinary viewer tends to qualify as more serious defects of free-to-air TV than the problems of compression typical of satellite TV platforms. Maybe forcing our networks with out-of-standard signals is a way to contribute to the discredit of terrestrial TV.

In the coming years we will have the urgent need to learn about new measurement systems, which allow us to ensure the integrity of the digital flows they will feed the new distribution channels, but in the meantime we continue producing and transmitting signals in baseband, and we must continue to take care of them as always, using the same systems of monitoring for coded signals that we have used in the last five decades.

In the coming years, many of us will have to face complex simulcasting scenarios during our migration to digital transmission systems, but still in those conditions will continue to have a bottleneck in the transmission, until we reach the definitive closure of the analog operations. This is why it is convenient to start making sure that our viewers see our products in a version appropriate to your reception conditions. After everything, they sustain us in business.