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Old July 3rd, 2005, 06:24 AM   #1
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AC3 too quiet ?

Hi,

I'm using Vegas6 to render my sound track to AC3 files. The Vegas manual doesn't contain much information on the AC3 encoding, and a search on the web yielded no info to solve my main problem : the ac3 audio is VERY quiet.
I tried to edit the presets to change the dialog normalization to -1 dB from default -27 dB. No change. I also tried the various modes ofthe "Dynamic Range Compression" on the Pre-processing page. No go. Am I doing something wrong ? When I compare an AC3-encoded to its MP3 source, the AC3 is MUCH (perhaps -24 dB) quieter .

Any ideas ?

Thank you
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Old July 3rd, 2005, 06:36 AM   #2
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Searching on "AC3" restricted to this forum yielded the following thread
(on the first page):

http://www.dvinfo.net/conf/showthread.php?t=40673
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Old July 3rd, 2005, 03:40 PM   #3
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Yeah you have run the audio file thru sound forge and use the Normalize filter with the RMS average box checked. That number is what you should set the dialog normalization filter to. On my last project I used -21 and film light for compression with good results, but it all depends on the overall rms of the project.

From somejoe at Doom9:
The dialog normalization parameter needs to be set to the LAeq level of your program material. LAeq stands for the long-term A-weighted sound pressure level. Loosely, this is the average volume level of your source material. Us lowly consumers really don't have a tool that can measure this parameter, but we can get close. Sonic Foundry's Sound Forge has a "Normalization" feature that can measure the RMS level of a .wav file. CoolEdit may also have a feature like this. To use it in Sound Forge, open your .wav file containing the movie audio. Go to "Process"/"Normalize". Select the "Average RMS Power (Loudness)" radio button. Then click the "Scan Levels" button. The displayed "RMS" level is very close (within 1-2 dB) to the LAeq level.

That RMS level is the number that the dialog normalization parameter should be set to. In other words, if the RMS level in Sound Forge shows as -17.6 dB, set the dialog normalization parameter in your Dolby Digital encoder to -18 dBFS.
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Old July 4th, 2005, 08:34 AM   #4
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When rendering to AC3 go into the custom menu and rest the "normalization" to -31 and the "pre processing" tab change BOTH LINE and RF to "NONE".
Both of these are found when you click on "custom" after going into the RENDER to AC3 menu
That will take care of the problem

Don
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Old July 4th, 2005, 08:29 PM   #5
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Thanks Don,
I shared the same frustration until I tried your setup. Works great!
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Old July 4th, 2005, 10:31 PM   #6
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Thanks for the rapid reply, Rob.

I tried the suggestion to change the Dialog Normalization to -31dB and
the Line and and RF mode profiles to None. This didn't work for me.
My workarounds are to render my Project audio to WAV or MP3.
I dislike the additional coding of the MP3 mode, but the WAV file
is written as PCM even though my DVD Architect project audio mode is set
to AC3. If this is the WAV problem is a bug, I'd like to report it.

Thanks,

Gints
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Old July 5th, 2005, 12:40 AM   #7
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>This didn't work for me.

Meaining, the audio was still too quiet.
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Old July 5th, 2005, 09:11 AM   #8
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The -31 method sounds like it might be a bit of a bandaid fix. It might work sometimes, and others it might not I would think. RF should not be checked for DVD work, but Line in is what DVD uses for output.
I suppose it would limit the dynamic range compression?

Check out doom 9's site here for a great description of these settings:

http://forum.doom9.org/showthread.php?s=&threadid=56020

I really struggled with ac3 until I when thru this process. One of the other problems you can avoid by doing this is the compression pumping sound that can be heard when using incorrect settings.
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Old July 8th, 2005, 04:38 AM   #9
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Thanks, Jeff. The article was quite informative. Why is two channel AC-3
set to such a low level ? Since the settings in the default preset are for dynamic range compression enabled and the dialog normalization set to -27 dB, is the general user generating a DVD with sound at a very low level ?
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Old July 8th, 2005, 04:53 PM   #10
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My guess is that the defaults for the ac3 setting assume a Theater environment playback prensentation with dolby equipment and loud volume settings. Not so good for most home theater setups. But also the professional audio workflow is different than many of us have access to in our digital environments.
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