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Mastering to DigiBeta – audio levels question
I’m about to output something to DB. I got the WAV files from the studio, laid them down under the picture in FCP, 4 discreet channels going to to the deck via SDI. I mapped each channel appropriately in FCP timeline (1 to 1, 2 to 2 etc.) and in the “sequence settings > audio outputs”, I selected 4 channels of audio outputs, dual mono, downmix -3dB (default for that config, it was 0dB for Stereo). When I play the sequence in FCP, the tone that was inserted by the mix house in front of the audio, shows up on DB as perfect -20dB on each channel. However when it comes to the actual program audio, it seems to be peaking at almost 0dB. I know that as long as it never goes above 0, I’m ok distortion wise but the specs from the network say that the audio should average -15dBfs and not exceed -10dBfs. Is it something I’m not understanding about digital audio and dBfs or the mixes are in fact too hot?
Also: if the specs are saying that ch1 is Program Left and ch2 is Program Right (3 & 4 – mono mixes), do they mean that it’s a stereo mix? So why would the mix house send me two mono files named Program Left and Right instead of the stereo mix? Does it mean in audio output tab I should choose Stereo Mix 0dB for these two? Or stick to my original plan of outputting 4 discreet mono channels?
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20 Replies
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[Michael Niemcewicz] “if the specs are saying that ch1 is Program Left and ch2 is Program Right (3 & 4 – mono mixes), do they mean that it’s a stereo mix?”
As long as they are panned right and left, they will be a stereo mix.
[Michael Niemcewicz] ” So why would the mix house send me two mono files named Program Left and Right instead of the stereo mix?”
Because that is how most places do that.
[Michael Niemcewicz] “Does it mean in audio output tab I should choose Stereo Mix 0dB for these two? “
No…then you will be making them mono.
[Michael Niemcewicz] “Or stick to my original plan of outputting 4 discreet mono channels?”
Yes, do that.
But that seems AWEFULLY high. At most they should peak at -6db. Did the audio post facility follow the specs?
Shane
GETTING ORGANIZED WITH FINAL CUT PRO DVD…don’t miss it.
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If reference tone is -20db on a digital scale, then peaks to zero are just wrong and not your fault.
the simple fix is to razor the clip after tone and then drop the audio by -10db to be broadcast compliant.
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Well, sure but I was hoping that I could rely on the paid professional for paying attention to the specs and take the responsibility for the levels. Now, if I alter this mix and it comes back for whatever reason, the mixer may turn around and just say “you tweaked it, you own it”.
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Don’t tweak it. Send it. If it gets kicked back, it’s on them. OR…call them and VERIFY the levels are where they should. I think they are still a bit high.
Shane
GETTING ORGANIZED WITH FINAL CUT PRO DVD…don’t miss it.
Read my blog, Little Frog in High Def -
Don’t bother sending it to be rejected. That is just a waste of time. Contact the audio people and make sure they make it broadcast levels.
Also, make sure that the producers bothered to provide them with the specs. Best to apportion blame where it deserves to be.
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I’m not a specialist in all things audio, especially when it comes to comparing levels in digital and analog domains. I just voiced my concerns based on what I saw on the Digi Bete meters: rock solid -20dB on the tone and levels approaching zero on the program. Specs are the first thing I send to mixers and they stand behind what they did:
“Specs call for an average mix level (not peaks) of -15 db. BTW: this can only be measured by a VU meter, NOT the peak meter in FCP. Also your average mix level cannot go over -10. (we do average -15 and we do NOT average over -10.”
I was actually looking and being concerned with DB meters but they DO show me the same thing FCP meters do. And I don’t have VU meter to compare this with.
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Mixer is wrong, simple. Your spec says audio can average -15 but not go over -10. They went for an average of -10, therefore mixed to a completely wrong level. Send it back, with the specs, and have them read it again. This is simple simple stuff for any post audio mixer. If they can’t follow rules like this on a simple spec sheet, I wonder how much business they’ll ever do. -10dBFs peak is a pretty standard thing in TV delivery for USA.
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Also – your deck’s meter IS a VU meter. Just not a very detailed one. However, this is PERFECTLY valid for reporting to you the correct VU levels going to tape. If you see even a smidge over that -10 line, send the mixes back. No reason any post mixer using software of the last 10 years can’t hit that perfectly.
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This comes up time and again when dealing with audio post that do more music than TV or movie work.
Sometimes I have to remind our own in house audio engineers they forgot to bounce the mixes at the proper levels.
happens all the time.
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Broadcast specs talk about dbfs levels which means db full scale on a digital meter, not a VU. A VU meter is not the correct scale to be judging broadcast levels on. -20dbfs tone is meant to show 0 VU.
-15 db or -10 db on a VU will correspond to -35 to -30dbfs digital scale – far too low. Forget VU meters and use the FCP digital metering or external meters on your digi or HDCam deck.
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