M4A/AAC playback makes some weird sounds

[vladkorotnev]

The m4a decoder makes a lot of high-frequency crackle and bleeping on some files.

Test case: http://vladkorotnev.me/webtunes/player.php?list=74&track=1
Listen to tracks 1 and 2.
Expected behavior: acceptable quality playback.
Resulting behavior: music along with bleeps and cracks around 10kHz and almost missing high frequencies.
The same files sound awesome in QuickTime 7.

The tracks can be downloaded (play a track and then click the right "down arrow" key in the player control display) and played in QuickTime to prove that it's not the files being low-quality.

Great JS plugin otherwise though, enjoyed building with it, thanks Audiocogs!

[devongovett]

Interesting. I think I hear it, but is there a specific timecode in one of those songs that you year it the most at?

[vladkorotnev]

Not quite timecodes but still.
Track 1:
00:32~00:35 [slight chirp]
~0:37 [even slighter]

It's 1 AM here so can't turn music on for a long time but I have added track 3 which is a copy of this video: http://www.youtube.com/watch?v=ZK0TvORCnA0 in m4a format.
Compare them, and at about 0:54 just before the main riff comes in you hear these chirps too.

[devongovett]

OK I'll take a look. Thanks for reporting, and by the way, awesome app!

[vladkorotnev]

Hehe, thanks, made a small video about it recently. http://www.youtube.com/watch?v=8XF-FwMMBEM
It would be nothing without your code though! Thanks a lot

[devongovett]

You should add a link to it to https://github.com/audiocogs/aurora.js/wiki/Known-Uses :)

[devongovett]

After fef4ab2 it sounds a little better, less pops I think, but I still hear some really high pitched overtones sometimes. Still looking.

[vladkorotnev]

Uh, now i need to figure out how to compile it and test it ^^''''

[mahadevan-k]

We've been experiencing the same issues on our platform too. I've tried forcing a resampling etc. nothing works.

We use VBR encoding via faac, and if the quality level is anything less than 100, the noise gets worse, at around 70-80 it starts getting impossible to listen to the audio.

Whoever fixes this is god lol

[justinddunlap]

I also hear high-pitched static, in my case with ADTS-encoded AAC. I can provide sample files if needed.

[mahadevan-k]

ADTS encoded AAC at our end too. Is this an ADTS specific issue?

[devongovett]

Sample files would be very useful, thanks.

[justinddunlap]

Here's an example: http://1drv.ms/1OrjGDf

[devongovett]

The reason it sounds weird in this case is that the file is encoded as an HE-v2 AAC file, which is not currently supported by AAC.js. The SBR (spectral band replication) data is being ignored currently, which accounts for the high pitched overtones you hear. See #1 for the open issue about HE-AAC support, and read more about it on Wikipedia.

[mahadevan-k]

Is there are similar problem with VBR as well?

On Sun, Apr 19, 2015 at 7:42 AM, Devon Govett notifications@github.com
wrote:

The reason it sounds weird in this case is that the file is encoded as an
HE-v2 AAC file, which is not currently supported by AAC.js. The SBR (spectral
band replication http://en.wikipedia.org/wiki/Spectral_band_replication)
data is being ignored currently, which accounts for the high pitched
overtones you hear. See #1 #1
for the open issue about HE-AAC support, and read more about it on
Wikipedia
http://en.wikipedia.org/wiki/High-Efficiency_Advanced_Audio_Coding.

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#4 (comment).

[devongovett]

@bitonator do you have a sample file?

[devongovett]

FYI work on SBR happening here: #13