AC3 and AAC questions

[Wishmaster74]

Hello everyone. I have been working with MEGUI now for 3-4 months so I am still a noobie at Bluray encodes.

At the moment, I am still trying to decide which audio format to choose. i have narrowed it down tho to AAC or Ac3 up to 640kbps.

I have tried multichannel AAC and AC3 audio both in my tests and i personally can not hear a difference between 640AC3 and AAC at approx 375kbps.

However, my current PC 5.1 speaker are not the greatest either, so this is likely why.
I do plan on purchasing some better 5.1 speakers later, so I wanted to ask a couple things to help me decide on a final format, to prevent recodes later.

I have been using the audio converter built in to MEGUI (nero and Aften) if this makes a difference.


My questions:
With neros multichannel AAC is it better to choose a Qf setting (of say .48 - .50) or a adaptive bitrate?

Normalize. What does this actually do? From my understanding it just raises the volume.
Should This be used with AAC multichannel OR with AC3?

Would AC3 be a better choice for audio over AAC?
If so why? Or rather what advantages/disadvantages will each have.

Any advice appreciated. Thanks

[tebasuna51]

With neros multichannel AAC is it better to choose a Qf setting (of say .48 - .50) or a adaptive bitrate?
Use always variable bitrate with Qf.
The 'Adaptative bitrate' in MeGUI (the ABR, average bitrate, option) need a second pass to be exact and a phisycal file like input. Soft like MeGUI/BeHappy, Foobar2000, ... send the audio data by STDOUT to NeroAacEnc and can't do the second pass.
Normalize. What does this actually do? From my understanding it just raises the volume.
Yes, amplify the audio until the max without distort.
Only needed if you detect low volume or when you downmix.
Need a second pass (inside AviSynth with a physical file input), the first check for the max volume value and the second apply the max gain possible.
Should This be used with AAC multichannel OR with AC3?
No matter the output format.
Would AC3 be a better choice for audio over AAC?
If so why? Or rather what advantages/disadvantages will each have.
AC3 is always compatible with hardware multichannel players, AAC isn't supported always.
Abot quality only know a test between multichannel formats: http://www.ebu.ch/CMSimages/en/tec_doc_t3324-2007_tcm6-53801.pdf

[Wishmaster74]

Thank you very much, and for the link.
Very useful information. Much appreciated!