AC-3 now always 24-bit?

ScorpioProd wrote on 5/22/2009, 9:50 PM

I notice in Vegas Pro 9, even though my project is set for 16-bit audio, when I do my AC-3 Pro encoding, it claims it is encoding as 24-bit.

Is this true? There doesn't seem to be ANY way to change it.

Is this any issue for DVD compatibility? I always thought all DVD audio needed to be 16-bit?

Thanks.

Comments

John_Cline wrote on 5/22/2009, 9:55 PM

No, DVD audio can be 24-bit.

ScorpioProd wrote on 5/28/2009, 11:45 AM

OK, but is Vegas Pro 9 really only encoding AC-3 at 24-bit?

Or is this not something I should be believing? It seems like there is a bunch of "data" permanently in the description fields when one goes to render in any format nowadays that one can't change.

gwailo wrote on 5/28/2009, 12:23 PM

if it is forced, it's not a bad thing...

it's what you should have been doing all along

Your mix creates a temporary uncompressed wav file at 24 bits instead of 16 bits then it gets repackaged into an AC3 data stream.

If the middle step (the temporary uncompressed wav file) has better resolution, it will result in a more accurate AC3 encode.

audio in "video DVDs" actually comes in 6 basic flavours, here they are in descending level of quality/fidelity:

1. Uncompressed 24bit - 96kHz PCM audio - 2 channels
2. Uncompressed 24bit - 48kHz PCM audio - 2 channels
3. Uncompressed 16bit - 96kHz PCM audio - 2 channels
4. Uncompressed 16bit - 48kHz PCM audio - 2 channels
5. Compressed AC3 stream - 2 channels
6. Compressed AC3 stream - 6 channels

AC3 streams don't really have a bit depth, just bit rates (the higher the rate, the better it is)
but it will never be as good as uncompressed PCM audio, just like mp3s will never be as good as uncompressed audio.

"Audio DVDs" can go up to Uncompressed 24bit - 192kHz PCM audio but player compatibility is uncertain - i don't think DVD architect even supports burning them

Bluray discs / HD-DVD discs advertise "true audio" this means they can actually have 8 channels of uncompressed 24 bit PCM audio at up to 192kHz (no more need for AC3, unless you want to save space) - but I don't think DVD architect supports this yet either