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ac3 vs. aiff level discrepancy

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Edward Cooper
ac3 vs. aiff level discrepancy
on Jul 20, 2009 at 3:18:21 pm

Hello,
I work at an audio post facility, so I should probably already know this, but you know... In preparing our reel in DVDSP, we mixed all audio to an aiff which peaks at -6dB. I then converted it to .ac3 with compressor, using the recommended dialnorm setting of -31dB and turning off all additional compression.
Simulating the disc in DVDSP with ac3 audio shows all levels to be identical to the aiff (-6dB), but actually burning the disc results in a DVD that peaks at 0dB. Interestingly, a disc burned with the raw aiff file does not change the audio level.
Does the Apple DVD player somehow recognize and normalize ac3 audio? Do standalone DVD players do this? Any help would be appreciated. I'd really like to preserve the levels we decided on. It seems like this is the opposite of the problem most people have with ac3s, namely, that their audio ends up too quiet because of dialnorm settings...

thanks,
eddie


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Michael Sacci
Re: ac3 vs. aiff level discrepancy
on Jul 20, 2009 at 4:10:26 pm

There are no meters in any of these programs have are you monitoring your peaks?

DVDSP is not normalizing your audio. It sounds like you have encoded it correcting and that you are just boosting the volume level on your output.



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Edward Cooper
Re: ac3 vs. aiff level discrepancy
on Jul 20, 2009 at 5:10:50 pm

thanks for the quick reply - mine somehow got erased, so here it is again:

We use precisely calibrated analog audio meters here, which receive their signal directly from the computer's audio interface. It's a great way of checking levels, particularly as TV mixing has such specific specs.

As an experiment, I ripped my own dvd and extracted the audio with quicktime pro - lo and behold, it peaks exactly where it should. That means to me that Apple's DVD player recognizes and somehow boosts ac3 audio to 0db. Again, DVD player did not boost the level of a DVD burned with aiff audio.

-Eddie


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Michael Sacci
Re: ac3 vs. aiff level discrepancy
on Jul 21, 2009 at 10:55:42 pm

I would never test monitor off DVD Player software, I would want only do it off of a high quality player.

Also is the ac3 a stereo or 5.1 stream?



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