iTunes AAC bad quality encodes, ABXable easily even at 192kbps VBR Options

[skuo]

Didn't Apple update the encoder between February and now? Is the bug still present in iTunes 6.05/Quicktime 7.1.2?

To my best knowledge, the fix will be shipped along with Mac OS X 10.5, and its previewed version will be available in WWDC 2006.

[Maurits]

Didn't Apple update the encoder between February and now? Is the bug still present in iTunes 6.05/Quicktime 7.1.2?

To my best knowledge, the fix will be shipped along with Mac OS X 10.5, and its previewed version will be available in WWDC 2006.

You wouldn't happen to know other fixes/extras in store for that version (gapless playback for instance), would you?

This post has been edited by Maurits: Jul 5 2006, 19:02

[drezon]

To my best knowledge, the fix will be shipped along with Mac OS X 10.5, and its previewed version will be available in WWDC 2006.

Good to know the bug report has been read (I wasn't actually sure about that) and a fix has been developed. This lets me hope that Apple isn't as bad as I pictured above (I was actually a bit exaggerating , though the MP3 issue still holds, as does the distorting eq, no gapless playback etc..).

Any chance for you to tell us when there will be a fix for Windows Quicktime / iTunes?

[rootkit]

excuse me, but what is this ABX?

[gaekwad2]

Sticky (in General Audio): What is a blind ABX test?

[Pepzhez]

Just redid the test with latest iTunes (6.0.5.20). As expexted (at least by me) still exactly the same.

I kept havng the same miserable results until today, actually. I updated to OS 10.4.8 and iTunes 7.0.1. Just tried encoding the "glockenspiel" file at 160 and 256 kbps VBR AAC, fully expecting the results to be the same, but, amazingly, the bug appears to have been fixed. Has anyone else noticed this?

This post has been edited by Pepzhez: Oct 1 2006, 09:18

[Serge Smirnoff]

...I updated to OS 10.4.8 and iTunes 7.0.1. Just tried encoding the "glockenspiel" file at 160 and 256 kbps VBR AAC, fully expecting the results to be the same, but, amazingly, the bug appears to have been fixed. Has anyone else noticed this?

No, I didn’t notice the “glockenspiel bug” disappeared (I used iTunes 7.0.1.8 on my Windows XP SP2 system), it still persists.

[Pepzhez]

...I updated to OS 10.4.8 and iTunes 7.0.1. Just tried encoding the "glockenspiel" file at 160 and 256 kbps VBR AAC, fully expecting the results to be the same, but, amazingly, the bug appears to have been fixed. Has anyone else noticed this?

No, I didn’t notice the “glockenspiel bug” disappeared (I used iTunes 7.0.1.8 on my Windows XP SP2 system), it still persists.

You're right. I took the time today to compare a bit more carefully. It looks like I got a little too ahead of myself. The artifacts are still there, but not as pronounced. However, there is a very noticeable difference since the 10.4.8 update. It appears that someone at Apple attempted some sort of fix to the encoder, but still didn't quite succeed. I guess it doesn't matter because broke is still broke, so I guess I'll just have to continue using LAME 3.97 mp3.

[John Lockwood]

...I updated to OS 10.4.8 and iTunes 7.0.1. Just tried encoding the "glockenspiel" file at 160 and 256 kbps VBR AAC, fully expecting the results to be the same, but, amazingly, the bug appears to have been fixed. Has anyone else noticed this?

No, I didn’t notice the “glockenspiel bug” disappeared (I used iTunes 7.0.1.8 on my Windows XP SP2 system), it still persists.

You're right. I took the time today to compare a bit more carefully. It looks like I got a little too ahead of myself. The artifacts are still there, but not as pronounced. However, there is a very noticeable difference since the 10.4.8 update. It appears that someone at Apple attempted some sort of fix to the encoder, but still didn't quite succeed. I guess it doesn't matter because broke is still broke, so I guess I'll just have to continue using LAME 3.97 mp3.

As a fellow iTunes user, I would like to extend my appreciation for your finding, reporting and pursuing this quality issue. However I am curious, as quality appears to be such an issue with you, why don't you simply use a lossless format like Apple Lossless? Doing so reportedly also apparently also improves gapless playback as well.

[kornchild2002]

John,

The point behind lossy formats like the iTunes AAC format is so you can carry your music around with you on your protable without eating a hole in the battery. So yes, quality is a issue but not the point of only putting 200 songs on a 60GB iPod just to retain that "true CD quality." Additionally, all updated 5G iPods, all 5.5G iPods, and iTunes 7 now support gapless playback of mp3 (both iTunes and Lame), iTunes AAC, apple lossless, wav, etc. files so there really is no need for lossless unless you want to have a digital backup of your CD's.

[drezon]

Just to let you know, I tested thunder.wav again with itunes 7 and I didn't notice any change. Stereo positioning still borked as usual..

I hope Quicktime 7.1.3 isn't the "fixed" version skuo was talking about.

But even if the fix finally comes with Leopard (due to somewhen in early 2007): one year to fix a (IMHO serious) bug in probably the most used AAC encoder is way too long. Especially considering that all iTunes-Store songs are encoded with a buggy encoder (with no way for the end-user to reencode) -- another reason not to buy lossy music.

[rpp3po]

As time went by, Quicktime 7.2 is out.

Any news on this front?

I'm still waiting to start converting a TB of flac files to AAC. This bug discovered by drezon really saved my day when he discovered it.

Quicktime 7.2 should be the version skuo was talking about - maybe prereleased due to the delay of the whole Leopard package.

Can anybody confirm that drevons discovery has been fixed? Apple had more than enough time to fix such a serious issue.

[rpp3po]

Damn, it is not fixed!

I just did a blind test using Westone UM2 directly plugged into my Mac Book. I instantly get 10/10 up to 256kbs AAC. The original thunder just cuts "sharper" through the sound stage.

That's really a shame. Skuo, can we expect anything different for Leopard, yet? For my ears that's unusable.

Apple is really risking very bad press about their new 256kbs "'Premium" tracks. Any audiophile journalist who picks this up could build a catchy story on top of simple, provable facts. That's not premium at all.

This post has been edited by rpp3po: Jul 15 2007, 18:38

[chrisgeleven]

You are worried about one killer sample that isn't really music? Every encoder has its killer sample.

[kornchild2002]

You are worried about one killer sample that isn't really music? Every encoder has its killer sample.

I was kinda thinking the same thing. Every encoder has killer samples. Even Lame has some samples that people can effectively ABX at 320kbps. I guess I don't see what the big deal is. It might be a bug but this bug is being heard on this sample (and probably a couple of samples). If Lame is allowed some killer samples, then can't iTunes AAC be allowed some as well? It is not like I use iTunes AAC (I use Nero AAC for their better VBR implementation and now the iPod/iTunes support gapless playback of Nero AAC files) but I think some people should cut it some slack instead of focusing on this one sample.

[Maurits]

Damn, it is not fixed!

[..]

That's really a shame. Skuo, can we expect anything different for Leopard, yet? For my ears that's unusable.

As previously mentioned, it is supposed to be fixed in the major encoder update that will come out together with Leopard. Since that upgrade is still a month or two away you shouldn't be surprised it is not fixed yet.

[kennedyb4]

You are worried about one killer sample that isn't really music? Every encoder has its killer sample.

You are right.

But I hope that Itunes vs Nero at some bitrate commonly used on portable players will be tested more widely asap.

[muaddib]

We at Nero are always willing to improve quality of our encoder, so whenever killer sample for Nero AAC Encoder is found please report it here at forum and we will check out what can be done about it.

[kenny01]

[quote name='drezon' date='Feb 8 2006, 16:03' post='362873']
After reading about the listening test here on HA praising 128kpbs iTunes AAC and such I decided to do my own listening test with real music I listen to.

I'm not very experienced with this, so I started at 64kbps to spot problem regions under the assumption that these will remain problem regions with similar artefacts at higher bitrates. Besides lots of other things I noticed that the stereo image was not correct, but thought this was normal for 64kbps (maybe its using is, or whatever).
However, to my surprise the stereo image problems remained up to 128kbps "VBR" (I was going in steps) and even at 192kpbs "VBR". I can't imagine no one noticed this untill now. Even 192kpbs is a piece of cake to ABX cause of this.

To make sure it's not the decoder I also decoded using iTunes with the same results.

Original sample can be downloaded here.
(Since I'm new to this: should I have uploaded the encoded version, too?)

The thunder right at the beginning is not correctly positioned. Also the second, higher frequency synth sound (the one that is percusion-like used and to the right, first used after the main synth "melody" begins) sounded strange at 128kpbs (and is also not correctly positioned) -- didn't bother to check at 192kbps.

Granted, the problem is not an anoying one -- I probably couldn't tell which is which without direct comparison, but anyways I'm less than impressed by iTune's performance.
I wouldn't have thought that AAC is so easy to ABX even at 192kbps VBR:

CODE

foo_abx v1.2 report
foobar2000 v0.8.3
2006/02/09 00:02:12

File A: file://H:\test\thunder.wav
File B: file://H:\test\_\_\_ 00 - _.m4a

00:02:13 : Test started.
00:02:42 : 01/01  50.0%
00:02:49 : 02/02  25.0%
00:02:55 : 03/03  12.5%
00:02:59 : 04/04  6.3%
00:03:13 : 05/05  3.1%
00:03:20 : 06/06  1.6%
00:03:26 : 07/07  0.8%
00:03:30 : 08/08  0.4%
00:03:45 : 09/09  0.2%
00:03:50 : 10/10  0.1%
00:03:54 : Test finished.

----------
Total: 10/10 (0.1%)

iTunes version used: 6.0.1.3

Can anyone confirm my findings? Is this a known problem.

Don't you have to use more samples for each test? I've noticed that I can get first 4 or 5 right because the abx program does not switch between the two samples (x, y) immediately. If your testing withing the first 15 seconds, one after another, they will all be the same. I think you should try about 20 samples over a 3 minute song to really just the accuracy of an ABX test.

[Ivan Dimkovic]

You are worried about one killer sample that isn't really music? Every encoder has its killer sample.

This is not a "killer sample" but rather, in my opinion of course, a bug in iTunes encoder - and I think a very old one.

Same problem with the same encoder happens with usual MPEG test clip called "glockenspiel" (forgot the exact name of the file, but it is easy to find it) at the end when bell sound goes into slow fade-out, the noise spectrum starts jumping up and down without apparent reason - it seems to be a bug in estimation of the AAC scaling factors, where too much noise is modulated almost few dBs below the signal energy.

I remember that one from long time ago (during time we were tuning our SF estimation ) and it is a bit strange people @Apple did not fix it yet.

This post has been edited by Ivan Dimkovic: Jul 16 2007, 21:40

[rpp3po]

This is not a "killer sample" but rather, in my opinion of course, a bug in iTunes encoder - and I think a very old one.

Exactly. This is no strange synthesized killer sample, but a stereo recording of a natural phenomenon.

Stereo recordings of thunders have very complex stereo images extending several kilometers. That's a perfect benchmark to separate men from boys regarding the preservation of spatial information. I bet that any natural recording of a thunder which has been recorded as close to the source as this one would make Quicktime fail at this point.

You may ask now why in hell would we need the capability to reproduce kilometer wide soundscapes, if we just want to listen to ordinary music? Well, a decoder which can handle a thunder just indicates very good algorithmic solutions for spatial representation. It scales from tiny space to landscapes and is able to represent images containing both without trade-off. It hints an elegant solution instead of a patchwork of special case optimizations.

And what about the sound of a great opera hall or plain reverbation in pop music? Artist like Björk work for weeks on the perfect sound of single samples. If you buy it on iTunes you may never know what she really had on her mind what it should sound like. Take this thunder sample. It brutally cuts through the scene in the original. The 256kbs Quicktime sample sounds completly "thundery" but severely misses the sharp cut through the scene. If a musician wants you to hear and feel that cut, he can't get this message to your ears using the iTunes AAC platform right now.

If Nero's encoder is able to handle this, I congratulate sincerely. I also appretiate muaddib's message about Nero's attitude towards problem samples. That encoder seems really worth that I give it a try.

I haven't followed the compatibility issues for a long time now. Can they be considered solved? I'm talking about iPod compatibility, iTunes tags and gapless playback on both.

This post has been edited by rpp3po: Jul 18 2007, 03:08

[menno]

I haven't followed the compatibility issues for a long time now. Can they be considered solved? I'm talking about iPod compatibility, iTunes tags and gapless playback on both.

As far as I know there are no known problems. iTunes/iPod handles the Nero gapless info (not the other way around, but in your case that doesn't matter I think). And the Nero tools write all the tags in iTunes and NeroDigital format by default.
Just have to make sure your files are called .m4a and not .mp4

[rpp3po]

A couple of days ago I said I'd give the Nero Digital encoder a try...

Now I have just finished an intensive listening session with neroAacEnc encoded files (drezon's thunder sample).

My ears' results (profile: Low Complexity):

1. Nero-AAC indistinguishable from original at Q 0.5 ~174kbs! - ABX: 8/20 ~ 86.8%
2. Nero-AAC slightly different from original at Q 0.4 ~134kbs - ABX: 15/20 ~ 2.1%
3. Nero-AAC at Q 0.4 ~134kbs light years better than Quicktime-AAC at 256kbs - ABX: 10/10 ~ 0.1%

Q 0.4 was VERY hard to differentiate and worked only with my Westone UM-2. Allesandro MS-1 didn't do it.

Good job Ahead!

This is going to be my new reference encoder.



Edit: For future reference: neroAacEnc 1.0.7.0, ABX scores added.

This post has been edited by rpp3po: Jul 25 2007, 16:37

[muaddib]

Nice to hear this
Thank you.
We will do our best to improve encoder even more in the future.