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  #1  
Old 01-21-2011, 02:52 PM
rabinrocks rabinrocks is offline
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Default Help! TV delivery specs question

Just a question from a newbie trying to understand audio level delivery specs for TV.

I'm mixing a short film and the requested delivery specs from the TV company is as follows:

a 1kHz sine wave at -20dBFS signal shall be used as the audio alignment signal level. This is equivalent to 0 VU, 1kHz in the NTSC analog standard 


master tapes with two-channel full stereo: channel 1 (Lo/Lt left) and channel 2 (Ro/Rt right). Audio channels must be phase coherent within 15 degrees at 10kHz

If anyone would be so kind as to explain this in layman's terms and what I should be using in Pro Tools to figure this out: Master Fader peak, phasescope, maxim etc.

I know this should be fairly straightforward, but for some reason I just can't grasp it.

cheers.
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  #2  
Old 01-21-2011, 06:54 PM
Postman Postman is offline
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Default Re: Help! TV delivery specs question

You have received a spec which is not very modern, or was written assuming you are a caveman. That doesn't make it bad, that just means it is from 5 or more years ago.
Quote:
a 1kHz sine wave at -20dBFS signal shall be used as the audio alignment signal level. This is equivalent to 0 VU, 1kHz in the NTSC analog standard
It is very, very common to have a "reference level" audio sinetone on a videotape, almost always playing under the color bars used for playback video setup. The sinetone level is at "0VU", which is the nominal, or approximate average, program level. In the US it is at -20dbfs. In other parts of the world the reference tone level is -18dbfs, 2 db higher. Regardless of the absolute level, it is an informal (with a long tradition) indicator of how loudly the program was mixed. A "reference point" if you will. Once a video deck's VU meter was set for "0" using a sinetone from your console while its meter reads "0", it was assumed the audio would be played from videotape at the correct volume. That was years ago, we've retained some of that mental approach but use newer tools and more specific definitions now. Now, for instance, we use loudness measurements that are derived in more objective ways than by someone gauging a VU meter by eye.

Quote:
master tapes with two-channel full stereo: channel 1 (Lo/Lt left) and channel 2 (Ro/Rt right). Audio channels must be phase coherent within 15 degrees at 10kHz
This is almost never something to sweat in an all digital world, it is left over from when analog decks had to be in excellent physical alignment to assure good mono combining of stereo programs. If all parts of your program combine to mono and still sound excellent, you should be okay. If the sound becomes oddly "flanged", you've got a problem.
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  #3  
Old 01-22-2011, 02:44 AM
mr.armadillo mr.armadillo is offline
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Default Re: Help! TV delivery specs question

Quote:
Originally Posted by Postman View Post
You have received a spec which is not very modern, or was written assuming you are a caveman.
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  #4  
Old 01-22-2011, 11:00 AM
critictalk critictalk is offline
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Default Re: Help! TV delivery specs question

Quote:
Originally Posted by Postman View Post
You have received a spec which is not very modern, or was written assuming you are a caveman. That doesn't make it bad, that just means it is from 5 or more years ago.
It is very, very common to have a "reference level" audio sinetone on a videotape, almost always playing under the color bars used for playback video setup. The sinetone level is at "0VU", which is the nominal, or approximate average, program level. In the US it is at -20dbfs. In other parts of the world the reference tone level is -18dbfs, 2 db higher. Regardless of the absolute level, it is an informal (with a long tradition) indicator of how loudly the program was mixed. A "reference point" if you will. Once a video deck's VU meter was set for "0" using a sinetone from your console while its meter reads "0", it was assumed the audio would be played from videotape at the correct volume. That was years ago, we've retained some of that mental approach but use newer tools and more specific definitions now. Now, for instance, we use loudness measurements that are derived in more objective ways than by someone gauging a VU meter by eye.

This is almost never something to sweat in an all digital world, it is left over from when analog decks had to be in excellent physical alignment to assure good mono combining of stereo programs. If all parts of your program combine to mono and still sound excellent, you should be okay. If the sound becomes oddly "flanged", you've got a problem.
How about using the phase scope plugin to measure the level?
There are different kind of meters shown in phase scope, VU, BBC, DIN, etc.
I don't think they have the same dynamic range, should they have different references?
Also, what is the average level of LEQ meter?
I always find out that when the mixing level is around -10db, the LEQ meter only shows up around -20, why?
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  #5  
Old 01-22-2011, 05:20 PM
mr.armadillo mr.armadillo is offline
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Default Re: Help! TV delivery specs question

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Originally Posted by critictalk View Post
I always find out that when the mixing level is around -10db, the LEQ meter only shows up around -20, why?
-10 is peak, -20 is RMS.
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  #6  
Old 01-22-2011, 05:59 PM
Postman Postman is offline
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Default Re: Help! TV delivery specs question

Hey critictalk,

First, I hope you are aware of the difference between peak levels (you say "-10") and averaged or rms levels (you say "-20"). If not, have a look here for some basics: http://myhometheater.homestead.com/rms.html

Our ears act much more like RMS meters than peak meters (a VU meter is like an RMS meter). I think you can benefit from some reading about what loudness measurements are and why our industry has begun to adopt them so much. An "leq meter", as you called it, has an rms meter at it's core. While an leq meter is not the same as rms meter, it is designed to keep a running tab on the "loudness" of our programs. Check out this document.
http://tech.ebu.ch/docs/techreview/t...ss_Camerer.pdf

I'm not sure if you'll understand every detail on first read-through, but it totally covers your questions. You are asking about an "leq meter". In that document look for "LUFS" (same thing as "LKFS") meter, which is a currently accepted type of "leq meter". The article's writer has a European background, so some terms may not be familiar. When he says "quasi peak" meters, realize those are another form of peak meter (not equivalent but similar). Your -10 readings came from a peak meter, I believe.

Good luck, this is technical stuff that is very important for broadcast, and not as important for film work.
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  #7  
Old 01-22-2011, 10:13 PM
critictalk critictalk is offline
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Default Re: Help! TV delivery specs question

Quote:
Originally Posted by Postman View Post
Hey critictalk,

First, I hope you are aware of the difference between peak levels (you say "-10") and averaged or rms levels (you say "-20"). If not, have a look here for some basics: http://myhometheater.homestead.com/rms.html

Our ears act much more like RMS meters than peak meters (a VU meter is like an RMS meter). I think you can benefit from some reading about what loudness measurements are and why our industry has begun to adopt them so much. An "leq meter", as you called it, has an rms meter at it's core. While an leq meter is not the same as rms meter, it is designed to keep a running tab on the "loudness" of our programs. Check out this document.
http://tech.ebu.ch/docs/techreview/t...ss_Camerer.pdf

I'm not sure if you'll understand every detail on first read-through, but it totally covers your questions. You are asking about an "leq meter". In that document look for "LUFS" (same thing as "LKFS") meter, which is a currently accepted type of "leq meter". The article's writer has a European background, so some terms may not be familiar. When he says "quasi peak" meters, realize those are another form of peak meter (not equivalent but similar). Your -10 readings came from a peak meter, I believe.

Good luck, this is technical stuff that is very important for broadcast, and not as important for film work.
Thx Postman
Thx for your help
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