Why Is Audio Volume Reduced by Default?

2G wrote on 5/20/2009, 7:17 AM
The default templates for the ac3 encoders are set by default to reduce the audio volume significantly. If I'm understanding the settings correctly, it pads the audio and compresses it down to about 25% of the original volume. This is supported by the fact that when I look at the audio on the DVDA timeline, it's very low volume (when it was max volume in Vegas).

I have played around with the ac3 parameters, change the pad, compression, etc. I can get the volume waveform back up on the DVDA timeline to what I would have originally expected. But at what cost??

I've proven that i can get the volume back up to 'normal'. But I'm sure this compression/reduction default wasn't an accident. What is the reason that DVDs have to have such low volume? What bad things are going to happen in the playing of my DVDs if I bring the volume back up to "normal"?

Can someone explain the philosophy behind this (and the potential side-effects if I bring the volume up?)

Thanks.

Comments

musicvid10 wrote on 5/20/2009, 8:05 AM
"The default templates for the ac3 encoders are set by default to reduce the audio volume significantly. "

What templates? What Vegas version? What encoder version (Pro or Studio)? What settings?
You need to be specific here.

If you are talking about the Dolby AC-3 Pro Encoder in Vegas Pro, with the DVD templates, I have some information for you.

If you will provide some specifics, I'll be glad to help.
2G wrote on 5/20/2009, 9:09 AM
Sorry. Yes, it's the Dolby Digital AC-3 Pro. "Default Template". I'm using V9. However, the default template for this renderer has been this way for many releases back.
musicvid10 wrote on 5/20/2009, 9:43 AM
OK, I have done some analysis of this.

First of all, regarding the Dolby AC-3 Studio 5.1 template, there is a minor bug that has been acknowledged by Sony. The 90 deg phase shift, which enables older Pro-Logic decoders, has been disabled by default. That is why I don't use it for DVD surround projects. The bug also shows up as out-of-balance downmixed stereo on the DVDA timeline, but not in the prepared dvd files.

Now, regarding the Dolby AC-3 Pro template, which your question is about.
-27 Dialog Normalization really means a -4dB average reduction, and -31 is unity gain (0dB or no reduction). Although I agree this is a silly default, I think they were going for an average "living room" level from uncompressed camera audio, and were not really thinking about the real pro user, who has already pre-processed his audio and would like to keep it the way it is.

The solution, which I have carefully researched and tested, it to set the following parameters in the AC-3 Pro custom settings, and then save it as a new preset template.

I've run some exhaustive tests with calibration test tones and done extensive reading of the Dolby metadata specs, and in reference to your question about the most accurate reproduction with the AC-3 Pro Encoder, I am prepared to make the following recommendations with notes:Hope this helps. I don't see any differences using the default template or the 5.1 dvd template as a starting point. BTW, I'm on 8.0c

TheHappyFriar wrote on 5/20/2009, 11:00 AM
I see this come up occasionally, this should be a sticky imho.
PeterWright wrote on 5/21/2009, 1:44 AM
Yes, I think it was good old Ed Troxel that came up with this a few years back - I've had a "Maintain Level" template in Vegas ever since. I still don't know though, why the "default" isn't like this.
Geoff_Wood wrote on 9/17/2009, 1:51 PM
Thank goodness for forum SEARCH after two days going mental over this 'problem' !

Certainlty this should be a standrd preset.

Audio level meters on DVDA would also be really helpful.

geoff