NeroAacEnc multi-channel - no coupling between front and back? Options

[sneaker]

Over at doom9 we had a little discussion about multi channel aac encoding.

I made a very small test:

I created three aac files of a 90 seconds stereo music file using neroaacenc 1.5.4.
1.) just stereo, i.e. two channels
2.) a 5.1 file, with the stereo on front left and front right channels, all other channels (center, LFE, surround) digital silence
3.) a 5.1 file, with the stereo on front and surround left and front and surround right, other channels (center, LFE) digital silence

File sizes:
1.) 1.46 MB
2.) 1.54 MB
3.) 2.94 MB

Sample 3 has almost exactly double the size of sample 1. It seems that neroaacenc doesn't do any "coupling" between front and surround channels, so that would confirm the assumption made by the thread start over at doom9. I have no idea why sample 2 has more "overhead" from the silent channels, than sample 3.


Can anyone verify the outcome of this test? Is this a Nero limitation or a limitation imposed by the AAC standard? Or does Nero increase the quality with more channels?

This post has been edited by sneaker: Sep 23 2011, 02:13

[lvqcl]

http://sites.google.com/site/qaacpage/news...multichannelaac

This page referres to ISO 13818-7 standard. As you can see, 5.1 AAC is really mono+stereo+stereo+lfe.

This post has been edited by lvqcl: Sep 23 2011, 04:20

[sneaker]

Ah, thanks. That was a perfect answer.

Do you happen to know if the same holds true for AC3?