Hey guys i was wondering ... for a 6 channel transcode, from an ac3 file, would a 192 LC or a 128 HE be better? Reasons why would also be nice too.

IMHO, use HE-AAC always up to 224-256kbps, on 192kbps is better to use HE-AAC. Reason is: 192kbps isn't enough for LC-AAC encode. For LC-AAC IMHO everything higher than 256 is good.

In my experience that's not valid in general, it highly depends on the contents of the AC3 stream instead. In a movie the AC3 part often consists of nothing but speech, some noise or even complete silence, i.e. an encoder which uses ABR (my preferred encoding mechanism for a movie's audio stream) can save lots of bits in these cases. This allows the codec to drastically increase the bitrates during actual music playback (far above 192 kbps) while still maintaining the specified average bitrate.

I Agree totality with you, but i will stick to HE-AAC for safe reason Aslo when i encode i apply DRC + normalize on AC3, that is aslo one more reason for encode as HE-AAC. In other hand i make some comparations, and looks like LC-AAC use much higher lowpass especialy on LFE, for lower rates.

Those "LC for 224+ HE for 192-" figures are probably valid for 2 channel streams only. Bitrate for 6ch is not like that.

No that is valid for 6ch, we are talking about 6ch, not stereo. This is overall bitrate so when i put 192kbps i get file wich have averge or constant bitrate of 192 dependly of ratecontrol i choose, and encoder internaly give every channel bitrate how much have in pool, but averge is 192. If i put 192kbps i will give file with strict file size, and same like if i encode 192 stereo file.

Starcy, What is ur reason behind putting HE up to 224? I was looking @ Nero Digital Profiles, for Rencode and the default values are usually 128 HE encoding.

If you encode with Nero CLI and use Automatic mode, encoder will automaticly choose best profile for that bitrate. CLI encoder in Auto mode AFAIK use HE-AAC up to 250kbps in Multichannel mode

My reason is keep more quality as possible. For example CT encoder alows up to 213kbps for HE-AAC in multichannel mode.

96-160kbps HE-AAC is good enough for example 1CD Rips were is video usualy H264/AVC or XviD. If you ABX 128kbps HE-AAC and even 96kbps HE-AAC both multichannel with original AC3 you will se that, difference is almost same like comparing original CD and 48kbps stereo HE-AAC.

160-192kbps sometimes is good in LC-AAC but like Junon says it depends of complexity of ac3 stream.

128kbps HE-AAC relly make good surround, and i have tons of moves encoded with 128kbps 5.1 AAC.

On AES.org alredy exist test between three audio formats, HE-AAC @ 160, AC3 @ 384 kbps, EAC3 @ 224

http://www.hydrogenaudio.org/forums/index....showtopic=54615

Back to topic: I'd prefer going for the 192 kbps LC-AAC solution in ABR mode. The reason for not choosing HE-AAC is hardware player compatibility, since I suspect you're about to rip a movie to an MP4 or an MKV file, which would be likely to be burned to a CD/DVD and watched via a DVD player then. Although many modern players claim to support the MPEG-4 standard I wouldn't be so sure about HE-AAC. And I wouldn't want to listen to a multichannel ~128 kbps HE-AAC file with half the sample rate and no SBR.

Edit: The hardware player thing only corresponds to MP4, of course. To my knowledge there's not a single hardware device which is able to parse the MKV container.

Im doing it for pc/xbox usage. XBMC does both lc/he AAC files.

Starcy what q level setting are you using for automatic mode? Are the q level for stereo mode about the same as multichannel audio? Corresponding to this.
http://www.hydrogenaudio.org/forums/index....showtopic=44310

No the quality mode isn't same for stereo and multichannel mode ofcourse. I preffer ABR or CBR and 2pass ABR over quality for multichannel. I usualy use 128 HE-AAC, but for better quality 192+ HE-AAC is recommended.

I'm about to make tiny DVD backups, and I would choose Nero AAC for multichannel reencode, but my test results were odd.

I made some test encodes to test how far I could push the bitrate. I would go for LC also for compatibility if it wouldn't take too much bandwidth. When i chose the -br parameter to set a given bitrate, the sound are terrible. When I set it to 320000 bit it's even worse than any other parameter.

Using the quality parameter, the sound are definately better, but not great until i reach ~420kbit with q0.4, and at that point it's a joke to reencode it for saving space, since most ac3's are 448kbit.

Is AAC just not the right choice for multichannel audio files, or is Nero AAC not optimized for it? Are there a better AAC encoder for multichannel files?