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Erik Pagan
which color bars to use
on Jan 18, 2012 at 5:22:47 pm

Hi. Probably a simple question but I don't want to mess this up. I shot a short film that's now making its festival run and I need to transfer a copy to HDcam tape. I shot it on a red and edited in FCP 6.5. The transfer house wants me to download a prores hq version for them and I want to put color bars and tone on the front of the tape. When I went to the color bars tab there were a number of options (some were for pal and I know those are definitely not it). The options available were: HD 1080i60, HD 25p/50i full frame, HD 25p/50i, HD 720p60, NTSC, some pal options and another that said more bars and signals. MY sequence settings are 2048 X 1152, custom (16:9), sq pixel aspect ratio, 23.98, "none" for field dominance fps and of course prores hq. Which color bars do I use for my HDcam tape? - Pretty sure we shot 1080p but that option isn't there.
Thanks


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Andy Neil
Re: which color bars to use
on Jan 18, 2012 at 6:19:02 pm

Use the 1080i bars. It's the proper frame size which is what you need. Don't worry about it not being 23.98. Just decide whether you want unity to be set at -12db (default) or -20.

Andy

http://www.timesavertutorials.com


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Erik Pagan
Re: which color bars to use
on Jan 18, 2012 at 7:30:38 pm

thanks - please explain the unity part of that - i know what decibels are but why -12 or -20?


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Jean-Christophe Boulay
Re: which color bars to use
on Jan 18, 2012 at 8:20:33 pm

Hi Erik,

The -12 or -20dB mentioned is the level of the tone in dBFS. It is the level to which VU meters' Zero level will be aligned to. It is the audio level of the tone in FCP as set in the viewer.

Basically, this should match the delivery specs you've been given and the reference level of your audio mix. If your mix was done at a reference level of -20dbFS=0 VU and you put a -12dBFS tone to which the playback system is calibrated, your mix will come out very low. If you go the other way round, you'll probably distort on the output and make a sound guy very angry. Everything should match.

If you realise your audio mix was done at the wrong level, that should be a quick fix for whoever did the mix. The overwhelming majority of audio specs for video delivery I've dealt with called for a -20dBFS=0VU reference level and most audio post studios are calibrated to that level.

IHTH,

JC Boulay
Technical Director
Audio Z
Montreal, Canada
http://www.audioz.com


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Erik Pagan
Re: which color bars to use
on Jan 18, 2012 at 9:36:40 pm

yikes - i have no idea what the reference level is - i did the sound myself using soundtrack pro 2.0.2 and a set of studio monitor headphones i bought for the occasion (mixed turned out great - listened to it on a variety of speakers - took me 100 times longer than it would have a pro but the one thing i have is time - unfortunately i cannot same the same with regards to money)

is there some default level to stp 2.0.2? - i just opened up the program and dropped it in


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Jean-Christophe Boulay
Re: which color bars to use
on Jan 18, 2012 at 10:15:20 pm

If you mixed directly in STP using its meters, you mixed to full scale. Relating this to an analog reference level gets pretty close to -12dBFS=0VU. Not exactly, but it's the closest standard and that combination used to be a standard for radio spot production so I trust it.

In the audio meter in FCP, which reads peak levels in dBFS, a -20dbFS=0VU mix normally peaks around -10dBFS to -8dBFS. A -12dBFS=0VU mix peaks at the top of the meter, around 0dBFS. You could use this as a rough target if you have to change levels to match specs. Festival specs are a little loose so you should be fine, but on a broadcast project this could be a real problem.

dBFS and V.U. can be quite confusing. More and more, specs only refer to the peak digital level in dBFS but any spec mentioning V.U. must have a reference level associated to it (ie. x dBFS = 0VU) and you need a V.U. meter to really measure your level. In your situation, you should be fine just adjusting the overall level of the mix if needed and refering to digital peak measurements, as read in FCP.

JC Boulay
Technical Director
Audio Z
Montreal, Canada
http://www.audioz.com


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Erik Pagan
Re: which color bars to use
on Jan 18, 2012 at 10:27:00 pm

thanks - man, nothing is ever easy
cheers


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Michael Gissing
Re: which color bars to use
on Jan 18, 2012 at 11:26:29 pm

Almost no broadcaster uses VU meters for critical QC. Broadcast specs are always in dbFS which means the standard digital scale. For NTSC countries -20db is the almost universal standard. Signal peaks should be no more than -10dbFS with occasional peaks to -8dbFS permissable. In the PAL world there is a standard of reference tone as -20dbFS and -18dbFS. Regardless of reference, peak levels should never exceed -10dbFS.

In a way the reference level is no longer important. Absolute peak levels are. The is also a lot of issues around apparent loudness with various scales being used to measure long and short term loudness. Many broadcasters use the Dolby promoted system and insist apparent loudness fall within a certain range. Mostly they are concerned about overly compressed material sounding too loud.

Check with your broadcasting contract about levels and audio deliverables. Did you create stem mixes of separate elements like music, narration, dialog and effects? The problem with avoiding audio post pros is not just money, but their ability to deliver both technical levels and deliverables.


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Andrew Rendell
Re: which color bars to use
on Jan 19, 2012 at 8:57:39 am

I'm in the UK - PAL world. Reference level here is ALWAYS -18dbfs, nothing else is ever used in broadcast.


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Michael Gissing
Re: which color bars to use
on Jan 19, 2012 at 10:55:36 pm

I am in Australia, also PAL and ref tone here is -20dbFS. Weird I know but...

International distributors also ask for PAL masters to have -20db tone as well, so when they do the NTSC standards conversion, they have the correct tone level.


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