Newbie 7.5 IRE Confusion…

[Graeme Nattress]

Digital video has no setup, and 8bit digital video works on a scale called REC601 which has black at code 16 and white at code 235, which FCP represents as 0% to 100%.

IRE is a strictly analogue phenonema. You have to worry about it if you convert analogue video to digital or digital video to analogue. You also have to worry about it in certain cameras, specifically DV cameras which don’t add setup correctly on the analogue outputs but fake it by recording black at code 32 on the digital scale, which produces “incompatible” DV tapes that need to be corrected in post.

What devices are you using to being in your analogue video or output analogue video. The control panel for that device will allow you to set the correct value of setup, 0IRE or 7.5IRE depending on your source or destination.

Capturing DVCpro50 over firewire is a digital transfer, so FCP just keeps the levels whatever they are on tape, which should leave black at 0% (code 16) and white at 100% (code 235). If you’re using the DVCpro50 deck as an analogue to digital converter for bringing in BetaSP into your system, you should set the menus to deal with the setup correctly on the analogue inputs and outputs.

Graeme

– http://www.nattress.com – Film Effects for FCP

[Matthewg]

Graeme, thanks for your response! Specifically, if I capture DVCPRO50 via firewire and edit and then MASTER via AJA IO componenet to BetaSP (which is still the broadcast standard where I work), how do I insure proper IRE???

[Graeme Nattress]

There’s a setting on the IO control panel that will add 7.5IRE setup to the analogue outputs. You should make sure that that setting is set correctly. I’d also, if you’re keeping a personal master, do a DVCpro50 master too to preserve the quality of your project, should you need to go back to the master and recapture as DVCpro50 is a very much higher quality format than BetaSP.

Graeme

– http://www.nattress.com – Film Effects for FCP

[Matthewg]

Sounds good! One more question: is it possible to add 7.5 to a program that is already 7.5, and if so, visually what does this anomoly look like?

[Chi-ho Lee]

Your blacks would not look as black. It would start to look grayish.

-CHL

[Graeme Nattress]

Yes. That’s right, and it’s something you’ve got to be careful of when you begin mixing analogue and digital video.

Graeme

– http://www.nattress.com – Film Effects for FCP

[Matthewg]

Wow, now I am getting a bit confused…so here is what I think your saying. If I capture pro50 via firewire and then master via component to betasp, I want to make sure my D/A box is ADDING 7.5. However, if I am capturing BetaSP footage to fcp via IO and then mastering back to Beta, I want to make sure it is not adding or subtracting. And if I am recording from betasp to Pro50 deck via component I want to Sub 7.5 on my Pro50 deck? And FCP just keeps the IRE level as whatever it was brought in as? so if I come into FCP via I/O BetaSP, my program will be at 7.5, but if I come in firewire off pro50 my project will be 0. Ow, my head is beginning to hurt.
Okay and for a broadcast overview question…if a tv station were working entirely in dvcpro (which some are) through the entire chain, when would the 7.5 be added (isn’t 7.5 the required broadcast standard)?

[Graeme Nattress]

“If I capture pro50 via firewire and then master via component to betasp, I want to make sure my D/A box is ADDING 7.5. ”

YES!

“However, if I am capturing BetaSP footage to fcp via IO and then mastering back to Beta, I want to make sure it is not adding or subtracting”

NO. The IO should be set to remove setup on input so that the blacks in FCP are at code 16 which is 0%, and the IO should add setup on output so that those blacks go to 7.5IRE on analogue tape. In FCP blacks should always be at code 16 or 0% on the FCP scopes. That’s because FCP is designed to to work correctly this way – just think of it as non-linear digital video tape, and think of dubbing Analogue to digital and then back to analogue.

“And if I am recording from betasp to Pro50 deck via component I want to Sub 7.5 on my Pro50 deck?”

YES!

“And FCP just keeps the IRE level as whatever it was brought in as? so if I come into FCP via I/O BetaSP, my program will be at 7.5, but if I come in firewire off pro50 my project will be 0. Ow, my head is beginning to hurt.”

FCP will, but FCP does not deal with IRE, but with digital video. IRE gets added or subtracted by the DtoA and AtoD converters in the IO.

Whenever you go from analogue to digital, you must make sure that your blacks end up at code 16 or 0% on the FCP scopes. To do this, you have to set the AtoD converter to correctly remove setup if present. Similarly on going from DtoA, you have to tell the converter to add setup if necessary.

“Okay and for a broadcast overview question…if a tv station were working entirely in dvcpro (which some are) through the entire chain, when would the 7.5 be added (isn’t 7.5 the required broadcast standard)?”

7.5IRE is the broadcast standard in North America only. If you submit a digital tape, then it’s not analogue and hence there is no IRE at all. Only when that tape gets converted to analogue, does setup get added if appropriate, and this will happen somewhere in the broadcast chain. If they are broadcasting digitally, it might even get added in the viewer’s home in their digibox.

Graeme

– http://www.nattress.com – Film Effects for FCP

[Matthewg]

Thanks a ton Graeme…I am thoroughly up to speed. I really appreciate your time and patience with me, you rock!