Hi All,

Since 5.5.10.35 has multichannel bug fixed, here is a quick guide how to encode multichannel files properly

1. Grab the alternative WAV input plug in from RareWarez (5.5.10.35 does not support multichannel wav-s by default)

2. Be sure that in the original 5+1 wav file the channels are ordered like this:

C, L, R, L", R", LFE

1 - Center Front
2 - Left
3 - Right
4 - Left Surround (Rear)
5 - Right Surround (Rear)
6 - LFE


This is because in Nero 5.5.10.35 plug-in still does not allow multichannel reordering from other configurations.

Also, new plug in version which will be available in the next version will have much improved multichannel bit allocation and more improvements in coding quality for all setups.

Thanks Ivan

Be warned though that trying to burn multichannel wav files to audio cd with the modified/hacked wav plugin from Rarewares Nero will probably crash.

Menno

I was using the AIFF output converter in BeSweet for my decoded AC3 files, works great ..,

People just can't help writing RareWarez >_<

heh

Does that also mean the channels in the aiff file must also be ordered like this?

Yes, otherwise it is possible that wrong pair of channels (for example Left and Left Surround, or Right and LFE) gets M/S (joint) stereo coded, which would lead to unmasking problems and definitely losing coding efficiency (because of low channel corellation).

Hmm, thank you very much for that bit of information since we were doing this a little differently at doom9 like this:
FL.wav
C.wav
FR.wav
Ls.wav
Rs.wav
LFE.wav
Basically, what some of us are doing is using something like azidts to transcode the dts track into six wavs and then create a little text file with all the file paths in the above order and then make that into a 5.1 aif. The ac3 tracks transcoded into 5.1 wav or aif in besweet would probably have this problem too. I guess someone should have asked before we started doing this to make sure it was right but I guess everyone assumed it was like ac3. Thanks again for sharing this with us before more of my movies got messed up,

@Ivan,

Probably a stupid question. I assume that the order of the channels in AAC is also:

C, L, R, L", R", LFE

1 - Center Front
2 - Left
3 - Right
4 - Left Surround (Rear)
5 - Right Surround (Rear)
6 - LFE

Is this the same ordering as what the other AAC encoders produce, like FAAC and aacenc?

@all,
Probably another stupid question. Can CoreAAC identify the ordering of the channels in an AAC, or does it assume a certain ordering?

Was there a specific reason NOT to follow the WAVE_FORMAT_EXTENSIBLE ordering of:

1. Front Left - FL,

2. Front Right - FR,

3. Front Center - FC,

4. Low Frequency - LF,

5. Back Left - BL,

6. Back Right - BR?

Well, such is the channel order defined by ISO standard for AAC - there is a way to overcome that, but I think that some multichannel players won't be able to decode signal with correct mapping then.

Anyway, proper direct show decoder (and encoder, if available) should read and write correct WAVE_FORMAT_EXTENSIBLE structure and make sure that AAC part is decoded/encoded properly, and channels reordered if need be.

I like the solution that will be present in QT 6.4, where you can actually choose channel ordering.

Actually, I am pretty confident that this is channel ordering of the input in order to match AAC ordering perfectly. New version of the AAC encoder in NeroDigtial will also be able to do that.

There is also another way of inserting channel order, by PCE elements in AAC but I would like to keep the default ISO channel configurations instead of putting of custom ones, just for the compatibility sake.

The problem is, as the channel order in WAV files is fixed (see here), one has to produce a custom WAV file with a "wrong" channel order, which is not easy for everyone.

On the other hand producing an AAC file with a custom channel order will only lead to interoperability problems and anyways there's no need for it. The right thing would be having a WAV input plugin that does the channel reordering and outputs the right channel mapping matching the one required for the AAC plugin. So everyone can use standard 5.1 WAV files as those produced by BeSweet -6chwav. The same goes for the AIFF plugin.

I hope this issue is solved on Nero 6, being otherwise a severe handicap for its AAC encoder IMHO.

We are working on it, in Nero Digital - user will have option to select input channel order, and the encoder will automatically reorder channels to fit AAC demands, and vice versa on decoding.

Where is the channel order defined? I can't find it the ISO standard. There is only a smple in the reference source.
Perhaps we should use some standarized channel order instead of the ISO example order.

BTW. The AC'97 order seems to be (another one):
Left
Right
Center
Left Surround
Right Surround
Low Frequency
Alternate Left
Alternate Right

Channel order in AAC is defined:

- by program_config_element
- by predefined channelConfiguration (most used I guess)
- or by definition in standard:
channels are ordered in the AAC from front to back starting with the front center and ending with back center if they are there (detected by detecting SCE instead of CPE), otherwise starting with frontleft1 and frontright1 and ending with backleft1 and backright1. LFE can be any and is easily detected by the LFE syntax element.

For normal usage (mono, stereo, 5, 5.1 and 7.1) channelConfiguartion works fine. program_config_elements are usually only used when there are multilanguage coupling channels in the file, so that a specific "program" for each language can be used.

Menno

Wow. Then there is no problem at all.

Knik,

You can find predefined channel configurations in description of AudioSpecificConfig structure in ISO 14496-3

It's on page 24 in 2001 edition of the standard.

Thanks. I already found it. I just used wrong keywords to search the pdf.