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9th October 2010, 23:11 | #1 | Link |
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LC-AAC and HE-AAC for 5.1 audio
I am trying to understand a bit more about multi-channel AAC. Can someone help?
1) What is the difference between LC-AAC and HE-AAC in multi-channel (5.1)? 2) For 5.1 audio, which one is better (quality wise)? LC-AAC or HE-AAC? (If the answer depends on the bitrate, please show me the details) 3) What are the available encoders for LC-AAC and HE-AAC? (for 5.1 audio) 4) Is there a "prefered" encoder, quality wise? 5) I've only heard about LC-AAC and HE-AAC for 5.1 audio, but is there a better (quality wise) AAC variant? Thanks, Simps |
10th October 2010, 00:41 | #4 | Link |
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Is the same for stereo or 5.1. With AAC-HE the high frequencies are encoded with a special method (SBR) than work better for low bitrates.
Then for better quality use high bitrates and AAC-LC encode. Please read http://en.wikipedia.org/wiki/Advanced_Audio_Coding
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10th October 2010, 00:48 | #5 | Link | |
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faac There is also QuickTime, but I don't use QuickTime since 1999. Nero encoder is usually regarded as the "b35t" freeware AAC compressor available. |
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10th October 2010, 14:30 | #6 | Link | |
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Thanks tebasuna51 and Midzuki.
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So, how do you encode 5.1 audio (6 mono .wav files) with neroaacenc? |
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10th October 2010, 15:00 | #7 | Link | |
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Nero also accepts input from stdin. edit: Wavewizard can combine the wavs. Last edited by nurbs; 10th October 2010 at 15:03. |
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10th October 2010, 16:11 | #8 | Link |
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Never use faac for any aac encoding, because is unfinished. NeroAAC, CTAAC (now Dolby) or QTAAC is freely avaible, and produce very high quality.
as input you need 6ch interleaved wav file. And keep in mind, never go below 300kbps if you use LC-AAC. |
11th October 2010, 00:49 | #9 | Link |
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Thanks nurbs and shon3i.
I think I will give AAC 5.1 a try. Since my source will usually be a 5.1ch ac3 or dts file, I will do this: 1) demux to 6 mono wavs with eac3to 2) mux the 6 mono wavs into a single 6ch wav (I will need to learn more about this. About the channel order, the tool to do it, etc) 3) neroaacenc. I think neroaacenc will automaticly set LC, HE or HEv2 based on the -q value, or the bitrate. So all I need to do is especify a "q" value, or a "bitrate". My goal is to shrink the audio files in the movies I encode for backup. I usually do AC3 5.1ch at 320kb/s. I hope I can shrink it to 256kb/s with AAC, keeping the same quality... we will see. |
11th October 2010, 03:53 | #13 | Link |
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Nero encoder can do 2-pass ABR. It makes sense for large files (in opposite of songs). Nero VBR is enough constrained but still admits some wider deviation of bitrate than ABR.
Nero goes for HE-AAC up to 200-220 kbps for 5.1 by default (recommended) and higher is only LC-AAC. Plus it depends a lot of compressibility. |
11th October 2010, 12:53 | #14 | Link | |
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11th October 2010, 18:14 | #16 | Link | |
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I will share an info that might be useful to someone... I encoded a 448kbps 5.1ch AC3 with eac3to input.ac3 output.m4a -quality=0.3 and this is what media info says about the output.m4a file: ------------------------------- Audio ID : 1 Format : AAC Format/Info : Advanced Audio Codec Format version : Version 4 Format profile : LC Format settings, SBR : Yes Format settings, PS : No Codec ID : 40 Duration : 3h 13mn Bit rate mode : Variable Bit rate : 222 Kbps Maximum bit rate : 308 Kbps Channel(s) : 6 channels Channel positions : Front: L C R, Side: L R, LFE Sampling rate : 48.0 KHz Stream size : 307 MiB (100%) Encoded date : UTC 2010-10-11 14:12:01 Tagged date : UTC 2010-10-11 14:25:42 ------------------------------- So, for this particular source (will change from source to source), -q 0.3 resulted in a 222kbps 5.1ch AAC file. Note that it is using SBR, so I guess this would be an AAC-HE, instead of AAC-LC. I did some blind test, switching between the 448kbps AC3 and the 222kbps AAC. They sound pretty much the same, with a tiny advantage for the AC3 file, pretty much negligible, very hard to detect. So, I would recomend AAC with -q ~0.3 for 5.1ch audio. This will save space, and will give you the chance to raise your video bitrate for more image quality too. I have only tested -q 0.3 with 5.1ch movie audio tracks. I don't know about stereo or music audio tracks, but I would imagine that for stereo music, -q 0.3 might not be enough, you might wanna use -q 0.35 or even higher values for stereo music tracks. Last edited by simps; 11th October 2010 at 18:27. |
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12th October 2010, 00:00 | #17 | Link |
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-q 0.3 is the boundary betwenn AAC-HE and AAC-LC, for that I recommend -q 0.35 at least to recode AC3 448 or DTS 768.
Still there are players without support for SBR part, then for a little more bitrate you obtain a more compatible stream. With the same sample: encoded -q 0.30 -> AAC-HE 231 Kb/s encoded -q 0.35 -> AAC-LC 266 Kb/s
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12th October 2010, 09:20 | #18 | Link |
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When it comes to playback, Quicktime player does not support AAC-HE (SBR) decoding. And the Pro version does not offer AAC-HE encoding...
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Last edited by SeeMoreDigital; 12th October 2010 at 09:22. |
12th October 2010, 13:38 | #19 | Link | |
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-q 0.30 -> AAC-HE 222 Kbps (SBR: Yes) -q 0.35 -> AAC-LC 260 Kbps (SBR: No) I did some blind test between both files, and I couldn't tell the difference. Dialogs were just as clean in both files. There were some explosions and gun shots too, and I kept going back into those parts to try to see a difference between the files, and I couldn't. The audio is from a war movie, so there were some pretty complicated parts, and also, some silent parts. I couldn't find a difference between both files in the blind test, and I did it with a good HI-FI headphone (AT-AD900) and a X-FI sound card. So, I guess the SBR algorithm is doing a really good job. 222kbps is 85% of 260kbps so you would expect a decrease in quality since 260kbps is already a bit low for 5.1ch audio, but for me, the quality was the same. I couldn't find a difference in the high freqs, or any other freq. I guess if one is concerned about compatibility, then might be good to avoid SBR, as you said, since some players won't be able to decode it. But if that is not a problem, I think there is no point to be afraid of SBR. It really helps compression, and I wasn't able to detect any change in quality, even with an AT-AD900. OF course, if you go down as much as -q 0.25 or so, I am sure quality will suffer a lot. And all of this is valid only for 5.1ch movie tracks. For stereo music, you would need a higher -q value, and no SBR. Both -q 0.3 and -q 0.35 will give you enough quality for 5.1ch movie tracks in my opinion. One will waste a little more bitrate, but will be compatible with more players. Anyway, thanks for all the help you guys provided in this thread. I learned a lot about AAC here. Last edited by simps; 12th October 2010 at 13:53. |
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17th October 2010, 03:52 | #20 | Link | |
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http://www.hydrogenaudio.org/forums/...opic=74781&hl= http://tmkk.hp.infoseek.co.jp/qtaacenc/ Last edited by IgorC; 17th October 2010 at 03:54. |
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