Skip to main content

Reader Feedback

Digital legal video level

In digital video, eight bits quantize 256 different levels.

The digital video uses values between 16 and 235 for video 0-100IRE.

Zero through 16 and 235 through 255 are overhead.

You said that the legal values for video are 0-100 (700mV); does that mean that levels higher than 100 are illegal in digital?

Is the -7-0 overhead 100-109IRE only a protection area that we should never use for video?

Is it a good pratice to set the white clipper at 100IRE for a digital camera integrated in a digital studio?
Claude Lessard

Michael Robin responds:

First, in dealing with component analog video we do not use the IRE notation. That is used strictly with analog composite NTSC. We express analog signal levels in mV. Levels 1 to 16 (-47.19mV to 0mV) and 235 to 254 (700mV to 763.13mV) allow for misadjusted or drifting analog video signal levels, as well as for possible overshoot and undershoot of analog signals. Levels below 1 and above 254 are not digitized, which results in clipping. Setting the camera clipping level to peak white (i.e. 254 or 763.13mV) would be duplicating the following digital equipment function so I don't think it is necessary. However, it would not hurt.

A la carte


I read with great interest your article in this month's [September] issue of Broadcast Engineering. As a religious program producer, I am greatly concerned at the impact a la carte availability would do to the religious programming market. Statistics show that while many enjoy the benefits of religious programming when offered through bundled channel options, few would be willing to pay higher charges for specific channels dedicated to carrying such programming. Not only that, but the higher rates cable outlets charge for such channels would reflect rate increases religious programmers would be forced to pay for such time slot availabilities. Religious programmers have had their hands tied long enough without the further injury of restricted or higher-priced cable outlets.
Rev. Ron Lambros
Rehoboth Baptist Church

Harry Martin responds:

Ron Lambros' comments represent the views of many specialized cable programmers, who feel they will be left behind if the FCC requires a la carte program packaging.

Currently, there is a notice of inquiry outstanding on this issue, but no specific rules have been proposed. Naturally, the cable industry is solidly against the proposal and has produced studies showing that cable rates would go up and diversity would be diminished if it were adopted. On the other hand, Congress has expressed a strong interest in a la carte as a way to reduce cable rates. That is what drove the commission to institute the inquiry proceeding.

Under these circumstances, my crystal ball says that the FCC will delay the matter as long as it can, give it serious consideration but then drop it. Others may have other opinions; no one really knows how this issue will come out.

September Freezeframe:

In September, we asked readers to submit nominations for the most unusual, distinguished or confusing names for television-related products.


Paul Byers, Sony PetaFile Frank Felker, CEL Maurice Tom Cupp, Accom Dveous digital effects; Spider Pod, Scorpion Pod

Test your knowledge!

See the Freezeframe question of the month on page 8 and enter to win a Broadcast Engineering T-shirt.

Send answers to