16-235 Broadcast safe?

[Sean McHenry]

I understand you are adamant about this but I have to take the other side and say this, both myself, a 16 year plus broadcast engineer and the chief of the local CBS OnO disagree with you on this one.

If you are going to DVD as your final output you may need to shoot at 0 as to the DVD player, you are a film source and film has 0 setup.

On the other side, all NTSC gear is going to insist to be right, it have a 7.5 setup, not 0. In my system, the 7.5 level is maintained throughout the project as I shoot 7.5, bring it in to the system at 7.5 and the Avid works with it at 7.5. When I send it back to tape it is at 7.5 and when it comes out of my DV decks to analog on the 528a scope, it's still at 7.5.

I think we are talking perhaps about the tonal range availble? 0 to 107 is a longer range than 7.5 to 107 but still, to be a legal NTSC signal, you must have the 7.5. Anything under 7.5 will not show up on a correctly setup NTSC monitor.

That's my version and I'm going to have to stand by it. I will be testing similar footage shot in both 0 and 7.5 going to tape and DVD. I will be checking the final analog output on the 528a we have here.

The question is not is it right in the digital realm but whether it is right in the final, analog world. 0 will simply be wrong in analog.

Other than the possible DVD issue, tape decks will not fool with your levels unless you ask them to. A tape in a DV/DVCam/DVCPro deck at 0 will shoot out the analog outputs at 0. The same tape with 7.5 will come out to the analog world at 7.5. The deck will not adjust so you must.

Until I hear a compelling reason other than "it's just not right", I'll continue shooting, editing and outputing to tape at 7.5.

Good rousing discussion.

Sean McHenry

[Sean McHenry]

As a follow up, please see this web site and read over the quote from it below:
http://www.adamwilt.com/DV-FAQ-tech.html#Setup

"Huh? Remember, I said "at NBC." NBC and their partners in crime will be using proper, broadcast/professional NTSC DVCPRO and DVCAM decks. Such decks have, buried in their menus, the option to "add setup". In Japan and Korea, that setting is properly turned off. In the USA, that setting should be on. By the same token the better camcorders offer "add setup" switches in their menus for their analog outputs.

A similar setting removes setup on incoming analog signals; it should be on in the new world, off in the exotic east.

Now, the Rest of Us may be using lower end gear: DSR-20s, DSR-11s, PD150s, even (shudder) consumer gear. None of these low-end decks and camcorders have "add setup."

So if you take a tape shot in a DV or DVCAM camcorder and play it back in one of these low-end decks, the analog output will NOT have setup. The playback will be fine in Asia, but it'll be "too dark" in the Americas.

However, the tape itself, and the recorded data on it, are absolutely and completely conformant to the 601 spec, because setup simply doesn't exist in the digital domain! The same tape plays back setupless in a DSR-11, but with setup on a DSR-2000 or AJ-D455 with "add setup" turned on.

But remember that that's only a parameter for the analog outputs! If you connect any of these decks to an NLE over 1394, they will all play back an identical image into the NLE, no matter how the switch is set. By the same token playing back (from the high-end decks) to an SDI monitor will always show a correct black at the same level no matter how you set the "add setup" switch. "

It covers both our sides. In digital, 0 is correct but to correctly output to analog western world NTSC, you must somehow get 7.5. I do it from the begining.

In the above we see that some decks have the option to add setup, just like the DVD decks. Most broadcast facilities and post houses have this set to off (as mentioned above) to keep from unintentionally doubeling the black level. They also employ trained people like me to setup each tape that comes through the facility manually so I can adjust if the level is 0 on the tape.

Most folks here in these forums are probably using gear that either has no setup option or their decks are like mine, DSR11 and DSR-20 or 25 and may not have an add setp option. Also remember this is to add it back in on the back end of the production. If you can't make it 7.5 in analog, and that is what television, plasma and LCD displays are set for, that would be wrong and you would be loosing some of that detail in the blacks.

Sean McHenry

[Graeme Nattress]

First Sean, Digital video is never measureed in IRE as IRE is an analogue measure. Digital video is measured in a 0-255 range, where 16 is black, always, and 235 is white. FCP for instance, which is what I'm familiar with, called this range 0% to 100%, but that's just a way of looking at things. The underlying video is at 16 for black and 235 for white, even if FCP won't let you see that.

If you set your DV camera to have setup added, chances are, it will be adding it in the digital domain, which is wrong, and that's because black is now at 32 and that is wrong, as black is always meant to be at 16. There is no such thing as setup or 7.5 IRE in the digital world.

For a DVD, it is digital, so black is at 16, or 0% or whatever your system calls it. This is correct. If you add setup in your camera, black is now at 32. The analogue outputs of the DVD player add setup, so your output analogue black is now at 15IRE - yuck.

Sure, if you shoot digital with black at 32 (not 16) play with it in your Avid, it will show in percentage terms black to be at 7.5IRE, but that's because Avid have done something silly and calibrated a digital scope in analogue units which have no meaning in a digital world, and if the analogue outputs of the Avid don't add setup, the output on your scopes will be 7.5% which looks right, but is only because you've added setup in digital where you shouldn't and not added it in analogue output where you should have!! The end result is that your camera has used the 32-235 range on tape, rather than the correct 16-235 range, which means you've only used 93% of the available 8bit space for the tonal range of your image, which in my mind means a 7% reduction in quality.

Any correctly operating DtoA converter in a DVCAM deck should, if in North America, convert a digital level of 16 to 7.5IRE. Many do not, but that does not mean that you compensate by putting your digital blacks at 32, but that you, instead, put a proc amp after the DVCAM deck and set it so that it adds 7.5IRE to the pedestal?

Remember, DigiBeta is also a digital tape format. It's 10bit, so that black is at 16*4 = 64 and white at 235*4 = 940. If you were to dub a 32 black DV tape over SDI to DigiBeta, the black on the digiBeta would now be at 32*4 = 128!! Which is obviously wrong.

Graeme

[Graeme Nattress]

Unless you're working with analogue video, 7.5IRE setup is just not an issue. You calibrate your monitor to your DV deck to your NLE, and remember that setup is "just" a brightness control, you set up your monitor pretending you live in Japan and so that the 0IRE black out of your affordable DVCAM deck looks correct. This is fine.

Making a DVD you must have the blacks set correctly at 16 in your camera, or else they'll come out grey. As most people on this forum distribute on DVD, that's totally correct.

Now for making a broadcast dub - you take your DVCAM black at 16 tape to your dub house, connect your DVCAM deck to your DigiBeta deck via SDI and that gives black on the DigiBeta at 64, (because it's 10bit) and that's also totally correct.

I thunk you read Adam wrong when you say: "Most broadcast facilities and post houses have this set to off (as mentioned above) to keep from unintentionally doubeling the black level. They also employ trained people like me to setup each tape that comes through the facility manually so I can adjust if the level is 0 on the tape."

If the pro deck correctly adds setup on the analogue outputs only (and conversely removes on inputs) it is totally correct to have that switch on to do so in North America, and off in Japan. If you record on your DV camera with setup on, and it adds setup digitally and puts blacks at 32 it is no longer 601 spec as Adam points out, and the correctly set up deck at the pro dub house will now produce blacks on your BetaSP tape after an analogue dub at 15IRE because you've added setup twice, and because digital video does not have setup, they were not expecting a digital tape to have black at anything other than 16.

Graeme

[Sean McHenry]

I think we are to the point where it won't make any difference what each of us believes in. I still have to disagree based on my broadcast, post experiences and the other engineers in broadcasting have to say about this one.

In the end, to have to fool your monitor by artificially setting the setup to a non NTSC level so it will look right is not something I plan on doing. the whole issue seems to come down to the thing you keep pointing out which is that 0 is correct for digital. Yes and no. Per Adams article, 0 is only proper in Asia.

As my normal output is to a DSR-11 or DSR20, I will shoot at 7.5 to give me the proper NTSC levels that will play back correctly on my NTSC monitor with the proper analog setup from bars.

After all, what if you need to look at analog footage on the monitor you just set up to fake 7.5 for DV? As you still have to get to 7.5 in the end, I'll hold that starting at 7.5 is simply more proper. That's how everyone in the broadcast world shoots here in Central Ohio.

The Sign Video page has a good article on setup and DV also but it fails to mention that you can set 7.5 on some cameras. They are doing something similar to your setup and telling folks to add the 7.5 at the end.

There is too much room for error in that method for me. Set it and forget it for me. You may have somethin gon the digi-beta dub however. I'll look more into that part too.

Do any of the plugins you have worked on come in PC flavor? I have heard some good things but I think they are for FCP?

See ya,

Sean

[Graeme Nattress]

No, the plugins are FCP only, although I am working on stand-alone software.

The setup issue is really simple. If it's digital it has no setup - never. Don't just ake my word for it - go look it up in the 601 spec for digital video. It's not a case of belief, but of demostratable fact, and the spec for digital video the planet over is identical, and it always has black at 16. If you arbitarily change that to compensate for your deck not adding setup on output then your tapes are incompatible with the rest of the digital world, and you've just made your post production house an island. If you shot tapes like that for me, for anyone else, they'd be rejected as not conforming to 601 spec.

Setup is only for analogue video in North America. It's not for digital video. Your compensatory method will produce bad DVDs, it will dub incorrectly to DigiBeta, and it will not work right with NLEs the world over.

0 is not right for digital - if you mean 0 IRE, as there is no IRE in digital. How can an analogue measure in milivolts have anything to do with 0s and 1s, or an 8bit or 16bit scale of integers?? Digital has black at 16, which is often represented as 0% in your NLE, but it's still 16.

Graeme

[Sean McHenry]

I understand but the idea of not being able to interchange with other NLE users isn’t right. The NLE will work with whatever you put into it. My Avid for example doesn’t care what setup (or lack of) I am using. I can just as easily send that tape to any other Avid, Premiere or whatever user and a good NLE will not take it upon itself to alter the video in any way. In fact, it will go back out the other side as 7.5 video and so on.

What this is telling me is that if I should be in a position to be working with both DV and analog footage, I need two sets of monitors, or to recalibrate them every time I change projects. On top of which, in the case of Avid and the ability to mix DV and other uncompressed SD formats, the DV better be at 7.5 on the way in. Otherwise I will need to force the blacks back up in the timeline for every clip I import. Or, as you mention, use a proc amp to force it on the way in.

It would be far easier and less prone to the vagaries of yet another physical conversion device to simply shoot it at 7.5 if the video is going to a mixed format edit. The same would be true of any other analog I/O.

As my last parting shot on this subject, and I think this is important to report, I called all my Engineering pals at various on air television stations to see what they have to say on the subject.

In speaking with the Chief Engineer of WBNS-TV (a CBS OnO), he says all his people shoot with 7.5. In speaking with the Engineering staff of WCMH-TV (the NBC OnO I spent 16 years at as an Engineer), all their cameras are set to 7.5. In speaking with the Engineering staff of UPN-53 (a Paramount OnO), all their DVCPro cameras are set to 7.5. In speaking with the current chief of the 3rd largest post house here in Columbus, Ohio, where I was chief for 3 years, he confirms that they indeed shoot digital at 7.5, edit at 7.5 and send things out at 7.5. They have done many DVDs in the time I was there with Miranda and Heuris real time MPEG-2 systems and have never had an issue with DVD setup or anything else using analog and SDI inputs to those systems. Their biggest client is The Limited, Inc. The head Avid editor is a beta tester for Avid and he confirms this flow. The stations freely exchange tapes with the networks all the time and have had no complaints over the years.

The reason they all shoot with 7.5 is that their final output is analog. In the analog world you need the 7.5 and it won’t matter a hill of beans if you bump the black level up on the front or the back side of the equation except as I mentioned earlier, you need to recalibrate your monitors to show you levels they weren’t meant to show if you shoot at 0 IRE. Another point about bumping up the black levels on NTSC monitors, you have some headroom in the dynamic range if you set for 7.5. If you pump 0 IRE to be where 7.5 should be you are changing the response of the monitor and that may alter other aspects of the image.

I will continue to follow the broadcast world and shoot at 7.5. If I need to go to DVD, I will export a QT Ref file (which requires very little render time) and bring that back into the Avid. I can then crush the blacks to 0 and make the DVD from that file. Seems like a better way than fiddling with your monitors and dragging them out of spec so you can view analog video that is out of spec just to make an occasional DVD. I and all the Engineering pals I have in Ohio are still recommending people shoot at 7.5 to make their analog output legal. In the end, we all view an analog signal.

That's about all I can possibly say on this one.

See you all in the funny papers (who said that anyway? I've heard that since I was a little kid.)

Sean

[Graeme Nattress]

1) how can you shoot at 7.5IRE on a digital camera as there's no IRE in digital video. I hope we're talking about digital cameras throughout here.

2) If such a camera has a switch or menu misnamed to be 7.5IRE it can work in one of two ways:

a) it can add setup on analogue outputs

or

b) it can add setup to the digital signal, shifting 601 black which is at 16 to 32, thus making that tape no longer 601 standard, but has the effect of outputting from the analogue outputs of the camera with black at 7.5IRE

3) DV, DVCam or DVCPro footage is brought into your NLE over SDI or Firewire.

4) If your DV deck does not add setup on the output, as many do not, then you have 2 ways of dealing with this:

a) put a proc amp on the analogue outputs to add 7.5IRE

b) raise your blacks in the NLE, from correct 601 levels of 16 to incorrect black levels of 32, loose 7% of your picture quality, but get 7.5IRE blacks on your output

5) if your DV deck does not have removal of setup on it's inputs, and you want to dub analogue tape to DV, or pass through analogue video into your system, you have two choices:

a) put a proc amp on the analogue input and remove the 7.5IRE setup

b) dub your analogue to DV, but your blacks will be at 32 instead of the correct 601 level of 16. You'll loose about 7% of your picture quality by not using the full 601 range, and you'll have to crush you blacks before exporting a movie to turn into an MPEG2 for DVD

6) You want to monitor the output of your DV system using firewire to a DV deck, out to your NTSC monitor. Your deck may, or may not, add setup:

a) your deck correctly adds setup to the analogue outputs. You can therefore calibrate your monitor to the deck / NLE and all is fine.

b) your deck does not add setup, so you pretend you're living in Japan and calibrate to the deck / NLE and all is fine until.... your monitor has dual inputs and you need to plug in a VHS deck, a DVD player, and a Beta SP player. All of them have setup on their outputs so you put a proc amp on the output of your DV deck.

So.... What can you do.... You can buy a proc amp, or a DV deck that correctly adds setup on the analogue outputs and removes it on the analogue inputs. I think JVC make an affordable one, and have a great flash movie explaining all this.

As for NLEs dealing with non-standard blacks. This does cause issues when filters and effects expect black to be at the correct 601 level of 16. Imagine a dissolve which is expecting to go to black at 16, and one where the images have black at the incorrect 32. The dissolve will look different in each case.

As for your TV experts, either you asked them the wrong question, they didn't understand your question, or like many TV station engineers, they don't know what on earth they're talking about, because if a DV camera adds setup in the digital domain, causing black to be recorded at 32 rather than 16, (like the PDX-10 certainly does - I know, I have one) then they are wrong.

Now, I haven't spent all day writing these posts to be an obstinate bastard, or an argumentative twat, but to try and be helpful and show understanding to the problems of dealing with setup in North America.

if you remember this, you won't go far wrong:

"Digital video does not have setup. Black levels on digital video are standard the world over at 16 for 8bit video and 64 for 10bit video. Often NLEs refer to this black level as 0%, but that is not IRE because IRE is a purely analogue measure, and has no meaning in the digital world."

and

"The correct place to add setup or remove setup is only on the conversion of digital to analogue, or from analogue to digital. Changing the black levels in the digital domain to compensate for incorrect setup on analogue inputs or outputs reduces quality and results in non standard digital tapes."

Or read what Adam Wilt has to say, and read it carefully, for he is correct.

Graeme

[Tony Hall]

Ok, I haven't read this whole thread because... well you wrote a lot, but I was just wondering what your thoughts for monitoring a DV cam on a waveform monitor are. I just got DV rack and I set my digital waveform monitor to 0IRE and it seems to give me a good idea of what's over/under exposed.

If IREs are irrelevant to DV, then how does DV Rack's waveform work? It's not basing it's readings on the cameras analog-out because the video is fed through a firewire cord. It's all digital.

I assume that the "setup" function on my new GL2 is completely useless as well since all it does is make it "look" like it's changing the setup, when all it's doing is washing-out/crushing the blacks in the video.

Rob Lohman (I forget how to spell his name) said that he changed the setup on his XL1 so that it was at the lowest setting (as opposed to the default). He thought that that was the setting that gave you a floor of 0IRE on a waveform. Initially, I did a test in DV Rack and it looked like he was right, but I had my waveform set to 7.5IRE instead of 0IRE. Now, it looks like the Canon Default gives you a floor of 0 and any change to this setting just crushes or washes out the blacks. On the DV Rack waveform, if you change the setup (on the GL2) so that it's all the way to the left, You get a concentrated line around the 0 mark... indicating that you're probably clipping information.

[Graeme Nattress]

Well, a purely digital waveform cannot be logically calibrated in IRE. If DV rack is doing so then they are pretending that their waveform is a real waveform when it cannot possibly be one. If the DV rack is correctly designed then the waveform should have black at 16 and white at 235, but I dont know what they are calling black on their arbitary scale. FCP, which is what I know best, for instance, called 16 black 0% and 235 white 100%. You only know what IRE that corresponds do after the digital has been converted to analogue, which, unless the DVrack comes with scope probes and works as a digital voltmeter, the DVrack software has absolutely no idea what voltage the digital 16 will be converted to by whatever Deck or camera you're using.

So in esscence, a purely digital waveform monitor with digital inputs should not be calibrated in IRE as it is meaningless.

Graeme

[Sean McHenry]

You will probably have to ask the folks at DVRack about how they base their measurements. They may be artifically telling us 16 in DV is the same as 7.5 IRE or 0 IRE, I just don't know.

I have played with DVRack and think it is the only way to measure what you are really getting. I just this week read a report on the PD150 and PD170 that say the analog outputs do not accuratly track the DV signal. That is to say, if you base your DV footage on the analog signal you see from the RCA or S-Video outputs, you are not really seeing what you are recording. This is potentially due to using less expensive D/A processing. I haven't looked into that any further.

I think the brick wall Graeme and I are on either side of is simply this:

The DV and or 601 digital spec says a digital level of 16 is the normal black level for digital video signals and 235 is the white level cutoff.

If you view UNPROCESSED digital through any D/A system, like a deck with the nefarious "add setup" turned OFF (or if it is lacking this adjustment, like the DSR-11 or DSR-20, etc), you will see the analog black level is incorrect for NTSC use. It needs to be 7.5 IRE. This would include by the way any dubs made straight from your camera to VHS, SVHS or any other analog source. If you have "0" as the setup on your DV camera, you cannot make a direct, NTSC legal dub via the RCA or S-Video outputs.

This means 2 things to me. I am going to have a hard time, unless I add some sort of D/A processing, like a Proc Amp to boost the black levels to 7.5, mixing any other footage from a betacam for example in my time line as the beta footage will have the 7.5 but the DV footage will not. I would have to either adjust each DV clip in the timeline to be at 7.5 or boost the level on the way in with a Proc Amp. That's a D/A and A/D trip that is actually unnecessary. Besides, I want to bring my footage in lossless via firewire, like it was made to do.

My contention is, if my DV camera has a 7.5 level adjustment, it is pre-correcting that digital footage I will be bringing in via firewire (so I don't have to leave the digital world via a D/A and then back to digital in my timeline).

Graeme is correct that this would violate the DV / 601 spec. To which I answer - so what? If I am in a closed loop, as broadcast stations and post production houses tend to be, I am only skipping a few steps that can potentially degrade my video. If my final resulting footage will be analog, and again, every glass viewing device in the US is NTSC, I am in analog and need 7.5 setup.

Just like boosting the black level to 7.5, it's just as easy to drop it down if I need to later.

As for the spec, there should have been a US 601 spec a long time ago to correct this oversight and this would all be a non-issue. If a US 601 said black was 32, we would have nothing in this thread to talk about. The spec would be right, the analog output would be right and DVD manufacturers would have probably done things a bit different.

GRAEME IS CORRECT, but only if you never leave the digital realm. Then again, everyone I know in the broadcast and post business is adding the setup at the source when possible, and it just plain works. See my previous list of who is adding 7.5 at the source.

Choose your path carefully however. Again Graeme is technically correct.

Sean

[Sean McHenry]

In a related question, to look at this issue backwards, if I am bringing analog footage into a DV deck, like the DSR-11 or DSR-20, what will the level be on my DV tape? I bet its a digital 32. Same as adding 7.5 at the camera.

Graeme, can you confirm this? I'm not at home right now.

Sean

[Graeme Nattress]

Thanks Sean. I put an email into the DVrack people asking how their scopes are calibrated.

As for workflow, if you're a pro house, or even semi-pro, the "correct" way to do things is capture, edit and shoot with correct 601 levels, and if you deliver on a digital format, then everything is fine. If you have to deliver on a analogue format (and in this day and age, if what you're doing is very pro, it will be a delivery on DigiBeta which being digital means there is no setup on it either) and you don't have a DV deck with a correct Digital to Analogue converter, then you should, as a matter of course, buy and correctly use a proc amp. It really is as simple as that.

As for any broadcaster, for them to be adding setup digitally on shooting is utterly ridiculous and I have to laugh. Everyone I know who broadcasts does so with a purely digital workflow from begin to end, wether they shoot BetaCamSX or DVCPro, and it goes direct from the camera over SDI to the edit suite, and from there to a large digital media server from where it gets played out, or even digitally over satellite to another city. Finally, it some point, it gets converted to analogue, and at that point, the DtoA is correctly configured to turn digital 16 to 7.5IRE.

It is very important for compatibility with the rest of the world to shoot proper CCIR-601 levels, and also for you not to loose 7% of your recordable dynamic range. The only occaision I can think of for using the setup switch on any video camera is if you're shooting something live, with an analogue connection back to a switcher, and you therefore need a correct analogue output. That's it. That's the only one I can think of.

Now for horror stories. My comments about broadcasters have brought to mind the fact that our local TV station is wired together with composite cable, not component!!! And as for NTSC black levels, some editors know less than nothing and get it wrong all the time.

And recently, I got some dubs done at a pro dub house. They were from Quad 2" to DVCAM, and they got the dub spot on. The blacks were perfectly at 16 and I was happy. Later that week I got some BetaSP to DVCAM dubs done at a local dub house, and the blacks were at 32ish, and I sent them back and complained like hell!! Standards are there for a reason, and I will not accept a dub like that as it does not adhere to international standards.


As for your situation Sean where you have to bring both Analogue and Dv into your system, I think the correct approach is:

DV over firewire - and shoot it 601 standard blacks and with no fake setup added.

To bring Analogue in via your DV deck, either as a DV dub or passthrough, you must remove the setup on the inputs via a proc amp. Yes, that's another piece of kit to buy. Or if you're using a pro capture card, it will have a switch to allow you to set the inputs to expect 0IRE or 7.5IRE for blacks, and that also takes care of things for you.

This way, your digital footage is kept pristine, and your analogue footage is not really harmed by going through a good quality proc amp. Or get a Sony J30 and bring in your SP over SDI or firewire and again completely avoid the issue.

Now for output, you can take a cop out and get that DV tape dubbed to digiBeta and forget about it. Digibeta being CCIR-601 has the same black levels (scaled because it's 10bit, but the SDI inerface takes care of that).

Or if you're doing it at home to you BetaSP deck, again, buy that proc amp. Or take the DV tape to a pro dub house and get them to make an SP dub as their DVCAM deck has a correctly set DtoA converter output.

There are many ways to solve the problem by use of a proc amp on the digital to analogue and analogue to digital converters, or by keeping to a purely digital workflow. One good suggestion on this forum is for client VHS dubs is to make a DVD (great for backup master if nothing else) and because your DVD player correctly adds setup and turn 16 int 7.5IRE, you can make a sweet VHS dub with no bother at all.

Hope that helps,

Graeme

[Tony Hall]

If you're trying to get your footage to VHS with the correct setup level... couldn't you just make a DVD master and then dub it to VHS. I read somewhere that NTSC DVD players add setup... so your VHS copy should look like your DVD copy.

[Tony Hall]

Oh, and I just posted a message at the DV Rack forum asking if someone can confirm what I think. I think that the waveform monitor in DV Rack is probably just based on percentages of brightness between 16 and 239 (they mention 239 rather than 236 in the user manual) just like the zebras and the histogram.