Old 1st October 2006
  #1
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Question Broadcast A/V limiting question....





i got a friend who asked a very interesting question and i figured y'all be the ones that could answer....

"fox news just screwed up and played, for a few seconds, one of the 'standby' feeds--colorbars on hold for incoming video. it said:

fox news
-18dBf
and then some other crap

what does the -18dBf thing mean? i was talking to a friend who's making a film soon about sound for film and broadcast, and i was explaining how limiters set a ceiling appropriate for broadcast. i said it was probably close to zero db. and i said that when those 'annoyingly loud' commercials sometimes come on cable channels, that those commercials are using a different, louder limiting scheme than the network programming is.

how wrong am i about all this stuff? does the -18Dbf mean that the fox ceiling for limiting is -18 db? or am i way off with this? i've been wondering about this ever since i began noticing these volume fluctuations on cable between certain commercials..."


and on the same subject, i thought "yeah, but what about the local commercials that are obsurdily loud? i get 'em alot down here....all the network stuff is the same volume, then theres a local car salesman that's damn near twice the SPL.....i've often wondered about that....i STRUGGLE to compete with 'commercial' levels, yet some A/V guy can get obsurd levels that's twice as hot....sup wit dat?"


thanks for the passin' the knowledge

wyd
Old 2nd October 2006
  #2
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It was probably -18dBFS, and was the reference tone level.

There is also dBFB, which stands for "Fair and Balanced."

DC
Old 2nd October 2006
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Quote:
Originally Posted by dcollins View Post
It was probably -10dBFS, and was the reference tone level.

There is also dBFB, which stands for "Fair and Balanced."

DC

dBf stands for dB's referenced to 1 femtowatt, or 10 to the -15th power. It's sometimes given as dBfW, but the -18dBf in this case may stand for -18dBFs. Most ADC's are set -0dBFs = +24 dBu. -18dBFs = +6dBu. I've seen -20dBFs more often as it equals +4dBu, but I've also seen broadcast referrences required at -14dBFs and -10dBFs. Not sure why they don't have a set standard though.


As far as the commercials being louder than the program material. You can always get the spoken word hotter before limiter degradation than music tracks, especially very busy mixes, you may notice that the background music isn't that much hotter, but the car salesmans rap and the zingers (sound fx) are. This has nothing to do with peak though, as the program and commercials both typically have the same ceiling set in accordance with the FCC's peak limitation, however the way to get that track louder and not exceed FCC peak limitations is by raising RMS. ITR, the car commercials likely have a higher RMS than the program material and peak gain is the same.
Old 3rd October 2006
  #4
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-18 dbFs is a standard calibration measure in broadcast.
Aes-Ebu (US and Europe) have decided that this is the level for audio alignment with test tones in digital transmissions.
dbFs means simply Full scale and is referred to the digital scale, 0 dbFs = digital clip = square wave = horrible sounds, so the international agreement has set this level for average transmission with a 18 dbFs headroom for transients and modulation, keep attention to the fact that when you think about the resolution of your converters (16 bit = 96 dbFs, 24 bit = 144 dbFs, theoric values) you have to think in negative, say we have a converter that give you a 122 db resolution, that means from -122 dbFs to 0 dbFs.
I can tell that is normal to print on tape at a voice level between -18 and -10 dbFs, but for example mastered musical videoclips from great european broadcasters reach 0 dbFs and are lowered in level when put on air.
In the analog world every country or broadcaster in the world had their standards but with digital equipment everything is more simple, less different standards and the AES-EBU digital standard is the most used.
When you prepare a broadcast limiter you know you have a standard at -18 dbFs for static tones but you can go up with the equipment as you like, even if rules do not permit to do this.
Let's say I set my brickwall to stop transients at -6 dbFs and then I multiband-compress my program as I can with my equipment: now I'm sure that I cannot go over -6 dbFs but if I have set the equipment properly I can achieve a great loudness, even if I change dramatically the sound of the original program, for example I can achieve an average program at -12 dbFs with brickwall at -6 dbFs.
A lot of broadcaster, tv stations and radio stations have nothing to do with something like a "conservative approach" in audio treatments: the goal is to reach the highest level in terms of perception at home.
The result is that a lot of stations transmit always at a higher level than was established by AES-EBU and they do often a little trick having advertisement more louder than the average program.

I hope to be clear, my english is not so good...

Andrea
Old 3rd October 2006
  #5
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Quote:
Originally Posted by Ronny View Post
dBf stands for dB's referenced to 1 femtowatt, or 10 to the -15th power.
It's never quite as funny when you have to explain the joke..........................

DC
Old 3rd October 2006
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wow! thanks for such a detailed explanation!....my theory was kind of like that....i was guessing "i think they do hyper-compress everything on broadcast networks...but they set the levels (maybe) at -18 and THAT is what the individual (local) station recieves, then the station brings it up after to something closer to 0dbfsd then it hits the antennas (or gets digitally streamed)....but when someone sends a 'homemade' (aka small budget) commercial, THEY don't send it to the station at -18db, and WHO WOULD anyway? so the station is pretty much runnin' on autopilot (audio wise) and they put the local commercial through, it hits their limiters (which are set real close to 0dbfs) and BAM! EVRYTHING LOCAL IS LOUDER!....."

does that make much sense?

again, y'all rock!
Old 3rd October 2006
  #7
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Quote:
Originally Posted by whosyourdaddy00 View Post
wow! thanks for such a detailed explanation!....my theory was kind of like that....i was guessing "i think they do hyper-compress everything on broadcast networks...but they set the levels (maybe) at -18 and THAT is what the individual (local) station recieves, then the station brings it up after to something closer to 0dbfsd then it hits the antennas (or gets digitally streamed)....but when someone sends a 'homemade' (aka small budget) commercial, THEY don't send it to the station at -18db, and WHO WOULD anyway? so the station is pretty much runnin' on autopilot (audio wise) and they put the local commercial through, it hits their limiters (which are set real close to 0dbfs) and BAM! EVRYTHING LOCAL IS LOUDER!....."

does that make much sense?

again, y'all rock!

The -18 dbfs is a reference level for tone at the beginning of the tape. This is how the station knows how to calibrate their VTR. Just like having tones on an analog tape. Where is 0? For broadcast they want where is dbfs? As for limiting and such most stations do not allow for more than a +14db peak ie -4 peak meter in this example. But the usual post spec that we deal with is -20dbfs =0vu. And if that is true then a +14 peak would be at -6db. There are some specific audio specs that most stations have or they will reject your program.

Hope this helps

Mike
Old 3rd October 2006
  #8
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-20 dbFs is the SMPTE digital standard, in fact you can find this reference level in broadcast VTRs, I don' know why they don't fix the reference to Aes-Ebu standards, probably there's a reason...
Aes-Ebu standard is the one for any digital transmission, satellite or digital terrestrial, and so for any digital recorder.
This is so important because we have less and less analog transmissions in the world, so any difference in reference standards is bypassed by the fact that a digital full scale is the same in any country.
No one can give a station a "hard driven master" with over compression and levels beyond the usual standard, all the settings I was referring to about limiter and compressor settings are done in the Master Control Room (we call it in this way in Europe), the room where stations have the equipment for transmission.

It's great to post here and to be in this great community,
thanks to everyone.

Andrea
Old 3rd October 2006
  #9
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Quote:
Originally Posted by dcollins View Post
It's never quite as funny when you have to explain the joke..........................

DC
Sure Dave, but jokes don't answer questions. Some people are going to think that dBf stands for reference to femtowatts, when it's so easy to add the s.
Old 3rd October 2006
  #10
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Quote:
Originally Posted by Ronny View Post
Sure Dave, but jokes don't answer questions. Some people are going to think that dBf stands for reference to femtowatts, when it's so easy to add the s.
I know I'm wasting my time here, but my hilairious joke was about an imaginary reference called dBFB. Not dBf, which would never ever be used in audio....

Fwiw, all audio I've ever generated for video was at a reference level of -20dBFS, which seems to be pretty standard in the post world. If "minister" is on here he can do 20 minutes about the various standards and protocols out there.

DC
Old 4th October 2006
  #11
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minister's Avatar
Quote:
Originally Posted by dcollins View Post
I know I'm wasting my time here, but my hilairious joke was about an imaginary reference called dBFB. Not dBf, which would never ever be used in audio....

Fwiw, all audio I've ever generated for video was at a reference level of -20dBFS, which seems to be pretty standard in the post world. If "minister" is on here he can do 20 minutes about the various standards and protocols out there.

DC
Ah, the old Borsht-Belt 20 minute protocol routine, or, "How to keep your audio levels in the Shecky Greene".

Dave, I am surpised you missed this : dBFS stands for deciBels Fox Sports.

As has been pointed out, this is Reference Level -- though, it is odd for -18 to show up on a 'merican Network... In Europe, Japan, Australia, some parts of South America it is a -18 DIGITAL FULL SCALE ref., and, yes, the Society of Motion Picture and Television Engineers standard is -20. a 1kHz tone is set to -20 dBFS on the playback and calibrated to be 0 dBVU on your meters and on your recorder. But, this is the reference level, not the ceiling... this allows the networks to align their playback systems to know how much headroom they have. Each Network is a little different, but your headroom could be 10 dB or 9 or 14. You have to read the deliverable Specs that come with your contract. In Europe, I believe, it is standard across the board of -18dBFS= 0 VU with instaneous peaks to not exceed -9 dBFS. MOSTLY, in Amerikka, it is -10 dBFS ceiling....But i have seen -2 and -4 from FOX. Fair and Balanced and LOUD!

when whosyourdaddy00 says :
Quote:
but when someone sends a 'homemade' (aka small budget) commercial, THEY don't send it to the station at -18db, and WHO WOULD anyway? so the station is pretty much runnin' on autopilot (audio wise) and they put the local commercial through, it hits their limiters (which are set real close to 0dbfs) and BAM! EVRYTHING LOCAL IS LOUDER!....."
i think you don't understand what Reference Level means.

when Ronny says :
Quote:
dBf stands for dB's referenced to 1 femtowatt, or 10 to the -15th power....jokes don't answer questions. Some people are going to think that dBf stands for reference to femtowatts, when it's so easy to add the s.
I think he doesn't understand that dBf stands for deciBel Fembot. IOW, how loud to make the sounds and vocalizations of the female-like androids that fight Jamie Sommers.... I mean, if you can't hear the Bionic Woman over the Level of the Fembots, what's the point in broadcasting the show?

Also, to "Who Could Perhaps Possibly Be Your Father Nought Nought", if your friend is doing a 'film' for festival or other distrobution, there are different standards and necesssities to deal with....so, they need to find those out rather than following the broadcast standard.
Old 4th October 2006
  #12
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Thread Starter
yeah, i think i get it now....so send a tone at the beginning of the audio before program material, and it should show up as whatever it is labled on your meters....

cheers, and thanks again

wyd
Old 4th October 2006
  #13
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Quote:
Originally Posted by minister View Post
Ah, the old Borsht-Belt 20 minute protocol routine, or, "How to keep your audio levels in the Shecky Greene".

Dave, I am surpised you missed this : dBFS stands for deciBels Fox Sports.

As has been pointed out, this is Reference Level -- though, it is odd for -18 to show up on a 'merican Network... In Europe, Japan, Australia, some parts of South America it is a -18 DIGITAL FULL SCALE ref., and, yes, the Society of Motion Picture and Television Engineers standard is -20. a 1kHz tone is set to -20 dBFS on the playback and calibrated to be 0 dBVU on your meters and on your recorder. But, this is the reference level, not the ceiling... this allows the networks to align their playback systems to know how much headroom they have. Each Network is a little different, but your headroom could be 10 dB or 9 or 14. You have to read the deliverable Specs that come with your contract. In Europe, I believe, it is standard across the board of -18dBFS= 0 VU with instaneous peaks to not exceed -9 dBFS. MOSTLY, in Amerikka, it is -10 dBFS ceiling....But i have seen -2 and -4 from FOX. Fair and Balanced and LOUD!

when whosyourdaddy00 says :

i think you don't understand what Reference Level means.

when Ronny says :

I think he doesn't understand that dBf stands for deciBel Fembot. IOW, how loud to make the sounds and vocalizations of the female-like androids that fight Jamie Sommers.... I mean, if you can't hear the Bionic Woman over the Level of the Fembots, what's the point in broadcasting the show?

Here's what Dr. Lyle Blackwell Professor Emeritus VIT Electronic Engineering deparment and Dr. James Cercone of the computer science department have to say about it.


dBf This unit is more recent and is a standard for the extremely low signal levels at the input of antennas, communication receivers and so forth. The reference is 1 femtowatt, or 10 -15 watt.

0dBf = 10 -15 watt
0dBf = 10 log (P/10 –15)

For an FM receiver, for example, the sensitivity might be given as 10 dBf. Since the standard input impedance for such receivers is 300 ohms, this would correspond to an input signal 1.73 micro volts. For an FM or television receiver, 0 dBf would represent an input signal of 55 micro volts.


I wouldn't quit your day job of writing tv serials if I were you, Tom, it's clear that you are talking dBA, I'm correctly relating what dBf means and where IT IS USED in broadcasting. Maybe it's possible that FOX didn't leave the s off because they were really talking dBf, the poster interpreted a background reference that the consumer isn't supposd to see and everyone automatically assumes it's a mistake for an audio reference signal, so you jokesters can joke all you want and the poster can take what I've said seriously.

DC, please call your next expert to the witness stand.
Old 4th October 2006
  #14
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Color bars 75% and a static test tone, usually 1 kHz, 400 Hz or 440 Hz, at -18 dbFs.
This is the international reference for digital transmission, Audio Engineering Society and European Broadcasting Union.
Probably this is what you have seen, alignment tools.
Matching between digital and analog meters differs for any broadcasters.

Andrea
Old 4th October 2006
  #15
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minister's Avatar
Quote:
Originally Posted by Ronny View Post
Here's what Dr. Lyle Blackwell Professor Emeritus VIT Electronic Engineering deparment and Dr. James Cercone of the computer science department have to say about it.


dBf This unit is more recent and is a standard for the extremely low signal levels at the input of antennas, communication receivers and so forth. The reference is 1 femtowatt, or 10 -15 watt.

0dBf = 10 -15 watt
0dBf = 10 log (P/10 –15)

For an FM receiver, for example, the sensitivity might be given as 10 dBf. Since the standard input impedance for such receivers is 300 ohms, this would correspond to an input signal 1.73 micro volts. For an FM or television receiver, 0 dBf would represent an input signal of 55 micro volts.


I wouldn't quit your day job of writing tv serials if I were you, Tom, it's clear that you are talking dBA, I'm correctly relating what dBf means and where IT IS USED in broadcasting. Maybe it's possible that FOX didn't leave the s off because they were really talking dBf, the poster interpreted a background reference that the consumer isn't supposd to see and everyone automatically assumes it's a mistake for an audio reference signal, so you jokesters can joke all you want and the poster can take what I've said seriously.

DC, please call your next expert to the witness stand.
Really, I am a comedian in a Composer and Audio Post Pro's clothing.

Ronny, I am aware of dBf. The paper you quote from, talks about an FM or TV receiver. Care to explain to the class watt (he he) a transimitting outfit is doing providing receiver input load information? Please also explain to the class, if 0 dBf has an input signal of 55 micro volts (are you assuming 300 ohms...or, is it .2739 µvolts into a 75 ohm load??? ) what is -18 dBf? and why would that be stated against the beautiful NTSC color bars? (i really think the guy simply didn't the 'S'...you have assumed that he is reporting accurately what he saw and when he saw it he didn't know what it was.... don't you think it plausible that he simply lopped off the 'S' and it was dBFS and not dBf ?)

CLEARLY i am NOT talking dBA ! since when do they use A-weighted mesurements in TV bradcasting? i am tawkin' dbFS to VU.
Old 7th October 2006
  #16
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Quote:
Originally Posted by minister View Post
Really, I am a comedian in a Composer and Audio Post Pro's clothing.

Ronny, I am aware of dBf. The paper you quote from, talks about an FM or TV receiver. Care to explain to the class watt (he he) a transimitting outfit is doing providing receiver input load information? Please also explain to the class, if 0 dBf has an input signal of 55 micro volts (are you assuming 300 ohms...or, is it .2739 µvolts into a 75 ohm load??? ) what is -18 dBf? and why would that be stated against the beautiful NTSC color bars? (i really think the guy simply didn't the 'S'...you have assumed that he is reporting accurately what he saw and when he saw it he didn't know what it was.... don't you think it plausible that he simply lopped off the 'S' and it was dBFS and not dBf ?)

CLEARLY i am NOT talking dBA ! since when do they use A-weighted mesurements in TV bradcasting? i am tawkin' dbFS to VU.

Sure it's possible they left the s off, I think I mentioned that possibility myself. I was carrying the tongue-in-cheek further, refering to the dBA with your comment on how loud the fembots were versus Jamie Sommers, not that he was seeing -18dBA on the color bars.
Old 7th October 2006
  #17
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if it is, as you suggest, dBfemtowatt and 0 dBf would represent an input signal of 55 micro volts (or 10 log (P/10 –15)), then what is -18dBf?

and does that number make sense for an input impedence? or is it a transmit impedence?
Old 9th October 2006
  #18
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Quote:
Originally Posted by minister View Post
if it is, as you suggest, dBfemtowatt and 0 dBf would represent an input signal of 55 micro volts (or 10 log (P/10 –15)), then what is -18dBf?

and does that number make sense for an input impedence? or is it a transmit impedence?
ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ.

DC
Old 10th October 2006
  #19
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Quote:
Originally Posted by minister View Post
if it is, as you suggest, dBfemtowatt and 0 dBf would represent an input signal of 55 micro volts (or 10 log (P/10 –15)), then what is -18dBf?

and does that number make sense for an input impedence? or is it a transmit impedence?

I have no idea, I'm only saying that dBf is a reference that I've seen in broadcasting. It's not what I suggest, I'm quoting from a paper written by Blackwell and Cercone, also you'll find the same description in the Rane Audio Encyclopedia. I've never used dBf myself for anything and can't speculate to what the poster saw on his tv, nor anything about a given tv stations broadcast specs. Andrea's explanation is as good as any and it's plausible that they just left the s off.
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