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neroAacEnc.exe and 6ch encoding efficiency ... ?
Sagittaire
post May 5 2006, 23:15
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I have little ac3 6ch 448 Kbps. I make these convertions:
file wav 6 chanels 6ch.wav
file wav 2 chanels 2ch.wav (default matrix 6ch->2ch conversion for BS)
six files wav FR.wav, FL.wav, C.wav, LFE.wav, SR.wav and SL.wav

1) Convertion with neroAacEnc.exe
I use this command line for all wav file
neroAacEnc.exe -q 0.3 -lc -if input.wav -of output.mp4

and I find these size for each mp4 files
2ch done 2497 Ko and 114 Kbps
6h done 8764 Ko
FL done 1574 Ko
FR done 1569 Ko
C done 1567 Ko
LFE done 725 Ko
SL done 1481 Ko
SR done 1533 Ko

well it's really curious:
- same quality level for individual chanel done less bitrate than 6ch conversion (8.32 Mo vs 8.55 Mo)
- for same quality level bitrate for 6ch and 2ch sould be simple scalling something like between x2.0-x2.5 ... here it's 3.5


2) Convertion with FAAC.exe
I use this command line for all wav file
faac.exe input.wav -o output.mp4 --tns -q 100

and I find these size for each mp4 files
2ch done 2552 Ko and 116 Kbps
6h done 6559 Ko
FL done 1212 Ko
FR done 1211 Ko
C done 844 Ko
LFE done 2497 Ko
SL done 1233 Ko
SR done 1240 Ko

well here it's normal:
- same quality level for individual chanel done more bitrate than 6ch conversion (7.00 Mo vs 6.40 Mo)
- for same quality level bitrate for 6ch and 2ch sould be simple scaling something like between x2.0-x2.5 ... here it's 2.57

If quality level is the same for each encoding (1.0, 2.0, 5.1 ... etc) then bitrate for q 0.3 6ch file should be in 5000-6500 Ko interal. Chanel coupling seem work for 2.0 but not for 5.1. Bug for multichanel or different quality level ... ???

This post has been edited by Sagittaire: May 6 2006, 02:31
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Garf
post May 6 2006, 08:48
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The reason is simply that the -q levels behave a bit differently in 5.1 encoding.

QUOTE
Chanel coupling seem work for 2.0 but not for 5.1.


You are enitrely wrong, channel coupling most definitely works for 5.1.

QUOTE
Perhaps an old bug for the "fast" preset ...


You are entirely wrong, the new encoder has almost no relation to the old ones.

PS. Making these kind of crazy hypotheses each time you don't understand some behaviour of the encoder is silly and annoying.

QUOTE
- for same quality level bitrate for 6ch and 2ch sould be simple scalling something like between x2.0-x2.5


I wonder based on what evidence you're making this statement smile.gif Do you have access to 5.1 psychoacoustics data that we don't?

What I'm saying is that the intermasking effects of such encodings aren't as well understood yet as we would like, and that you shouldn't be surprised if we manage to drop the bitrate demand of 5.1 encodes very significantly in the future smile.gif

This post has been edited by Garf: May 6 2006, 09:04
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