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How can I verify HE-AAC and HE-AAC v2 support?
henrikk
post Apr 3 2013, 14:36
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My 2012 car decodes aac (.m4a extension) files fine (files are stored on a USB flash drive). The manual simply claims "aac" support but I cannot fine anywhere any specifics in regards to "LC" "HE", HE v2", etc. Question: how can I verify empirically if the media unit has HE-AAC and HE-AAC v2 support? The car does decode HE-AAC files and play them (as expected), but that does not mean it does it correctly.

OK, some will say listen to it and you can tell. Not sure I can. Well, then it does not matter. Maybe, but I still want to know.

Is there a way to tell except by having a attuned ear? Are there some special tracks one can use where the lack of HE support are especially noticeable? Any ideas?

Thanks,
- Henrik
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azaqiel
post Apr 3 2013, 14:45
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if I understand the questions correctly:

with regard to whether or not your car supports HE-AAC... you hear audio if the car supports it, otherwise you don't. with regard to whether or not your car does it correctly... I think you might mean quality, in which case, no one can figure that out for you.

but definitively, if your car plays HE-AAC, it's supported.
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db1989
post Apr 3 2013, 14:49
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QUOTE (azaqiel @ Apr 3 2013, 14:45) *
with regard to whether or not your car supports HE-AAC... you hear audio if the car supports it, otherwise you don't.
Not necessarily. Some decoders will simply ignore the additional SBR info that define the HE- part of the format and simply play the rest of the stream as though it were LC-AAC. Older idevices do this, for instance.
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henrikk
post Apr 3 2013, 15:29
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QUOTE (azaqiel @ Apr 3 2013, 08:45) *
if I understand the questions correctly:

with regard to whether or not your car supports HE-AAC... you hear audio if the car supports it, otherwise you don't. with regard to whether or not your car does it correctly... I think you might mean quality, in which case, no one can figure that out for you.

but definitively, if your car plays HE-AAC, it's supported.


My understanding of HE-AAC is that AAC LC only decoders will decode HE-AAC but simply not be able to reconstruct the SBR or PS portion of the data stream --- so they will work, just not as well as they should. Here is a quote:

"MPEG-2 and MPEG-4 AAC LC decoders without SBR support will decode the AAC LC part of the audio, resulting in audio output with only half the sampling frequency, thereby reducing the audio bandwidth. This usually results in the high-end, or treble, portion of the audio signal missing from the audio product."

on which I based my understanding. If that is incorrect, then I like to know. Hence, I should be able to hear it, hence my original question.


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saratoga
post Apr 3 2013, 16:13
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Encode a test file with a lot of higher frequency sound added. If it sounds weird its probably just decoding the lc part.

For what its worth you have to pay to use the he part iiuc. If they don't mention he they probably aren't paying.
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LithosZA
post Apr 3 2013, 16:24
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HE-AACv2 file on LC-AAC decoder: Missing the reconstructed high frequencies from SBR information. So try to remember how it sounds on your PC.
HE-AACv2 file on HE-AAC decoder: Missing stereo information from PS. Will be played back mono. Try a file with lots of stereo separation?
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Big_Berny
post Apr 3 2013, 17:12
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Maybe there's a demo file somewhere which only has SBR informations and the rest (LC part) is silence?
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henrikk
post Apr 3 2013, 17:14
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QUOTE (LithosZA @ Apr 3 2013, 10:24) *
HE-AACv2 file on LC-AAC decoder: Missing the reconstructed high frequencies from SBR information. So try to remember how it sounds on your PC.
HE-AACv2 file on HE-AAC decoder: Missing stereo information from PS. Will be played back mono. Try a file with lots of stereo separation?


On a PC that *does* support HE-AAC & v2, how can I force it to decode an HE-AAC stream as AAC-LC so that --- on good equipment --- I can listen to what a HE-AAC audio stream decoded as AAC-LC sounds like? I'd like to train my ear to hear the difference.



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henrikk
post Apr 3 2013, 17:15
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QUOTE (Big_Berny @ Apr 3 2013, 11:12) *
Maybe there's a demo file somewhere which only has SBR informations and the rest (LC part) is silence?


That would be awesome... if such an item existed.
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Big_Berny
post Apr 3 2013, 17:35
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I found this: http://lists.apple.com/archives/streaming-...g/msg00007.html

There are files for HE-AAC and HE-AAC v2. Maybe you have to change container first as it's stored in a 3gp-file.

EDIT: I think on the server there are other versions (m4a and mp4) of the same file: ftp://ftp.orban.com/1010/Calibration/aacPlus_Test

This post has been edited by Big_Berny: Apr 3 2013, 17:38
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mixminus1
post Apr 3 2013, 17:52
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Useful files, thanks, but all encoded at 0 dBFS?!

Turn your volume *way* down before playing these!


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henrikk
post Apr 3 2013, 18:07
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QUOTE (Big_Berny @ Apr 3 2013, 11:35) *
I found this: http://lists.apple.com/archives/streaming-...g/msg00007.html

There are files for HE-AAC and HE-AAC v2. Maybe you have to change container first as it's stored in a 3gp-file.

EDIT: I think on the server there are other versions (m4a and mp4) of the same file: ftp://ftp.orban.com/1010/Calibration/aacPlus_Test


Wow! Exactly what I was looking for. I will download and test.

Than you!!!

- henrik
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Big_Berny
post Apr 3 2013, 23:29
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No problem. smile.gif

Don't forget to read the description on the website how to find out if he-aac or he-aac v2 is supported. And report if it worked!
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henrikk
post Apr 4 2013, 01:34
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QUOTE (Big_Berny @ Apr 3 2013, 17:29) *
No problem. smile.gif

Don't forget to read the description on the website how to find out if he-aac or he-aac v2 is supported. And report if it worked!


Here are the results. The 32kbits/s test file will not play at all in my car stereo. By that I mean, they do not behave the way described --- the system just errors out ("unplayable file"). Strong clue #1 that HE-AAC v1/v2 are not supported. However, since I had already discovered earlier that the car would not play regular AAC-LC files of 32kbit/s or less I am not yet 100% certain. So, test #2: I converted the HE-AAC and HE-AAC v2 test files to 48kbit/sec. I verified they work on my PC as expected and are proper HE files. When played in my car they confirm what I suspected: both the the SBR and PS test files play in the sense they do not error out. The PS test file gives me a nice mono tone (no stereo) and the SBR test file is silent (but plays).

So to conclude. My car does not support HE-AAC and HE-AAC v2.

Thanks everyone for their help!

- Henrik

This post has been edited by henrikk: Apr 4 2013, 01:35
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mixminus1
post Apr 4 2013, 03:59
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For future reference, what is the make and model of your vehicle?


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henrikk
post Apr 5 2013, 20:08
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QUOTE (mixminus1 @ Apr 3 2013, 21:59) *
For future reference, what is the make and model of your vehicle?

2012 BMW 328i with all available multi-media related options. I believe this is the same multimedia unit found across all BMW's (low to high end 7 series) and even Rolls-Royce cars. Of course it is possible different cars have added functionality, I doubt it.

Note, however, BMW completely redesigned their multimedia unit in 2012. My unit is the CIC-2008 (latest 2012 firmware) and the new one is CIC-HIGH(NBT)-2012. Here is a snipped about their new unit: "The current CIC unit already provides a highly optimised Multi-Media Interface (MMI) so the objective of NBT is to focus on design and performance." So I am not hopeful it has proper HE-AAC support, but I do not know.

- Henrik
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