|Reader Comments/Tips on AAC Encoding Sound Quality
Last Updated: 5/1/2003
Tuesday's (4/29) news had some reader comments on AAC encoding quality (noise reported by one reader originally), several other readers replied to that post with their experiences and suggestions.
Reader Feedback (most recent first)
I'd suggest turning off the Sound Enhancer option in the preferences of
iTunes. (to address the first reader's comments on some sort of noise/distortion in the encoding) That makes it sound far better to me, and I usually use headphones.
Sometimes just lowering the level of enhancement can help too, but if you
want to hear the song as intended, off is best.
I'm not 100% sure, but I thought I had the Sound Enhancer off in iTunes 3,
but it was definitely on after I installed iTunes 4.
as an FYI, I purchased 3 single tracks and an entire album from the
Music Store for testing purposes. I was extremely pleased with the CD
burned from them, the quality in my car stereo rivaled XM radio, and
was better than the commercial Audio CDs I have played in it. The
stereo is the stock 2003 GM 6 disc unit with XM and BOSE - 2003 Chevy
Avalanche Z71. I am going to re-rip my entire CD collection to AAC, as
most of it was ripped at 96k mp3.
Same here. Ripped Rodrigo's Concierto de Aranjuez, more out of
curiosity than anything else, to AAC highest possible quality. At least
twice, it sounded as if the music 'skipped'. My sound system is a
Logitech Z-680 which sounds good when music is played from a CD
directly. Haven't had any other problems with iTunes 4, and haven't
tried QuickTime 6 with AAC. I'm not much of a ripper anyway...
I am a professional musician and have been recording music on my Macs for several years now. I have tried encoding AIFF files/CD tracks with the new AAC coding feature in iTunes 4 at various bit rates. I got some pops and clicks at 128 kbs. I then tried encoding again, this time from a different CD player (internal superdrive rather than the external firewire DVD-RAM drive I used before). No problems this time, at bitrates of 128, 160 or 190 kbs. It is possible that the older drive has less sophisticated error correction, and AAC coding is accentuating the media errors (garbage in – garbage out)? Media errors seem to show up as artifacts in only one channel, like I was getting. Still, coding from the newer drive with a scratch-free CD produced great results at most bitrates. I still want to try coding different types of music from different media sources, at different bitrates. I am still trying to determine what AAC bitrate will give equivalent quality to my previous preferred mp3 coding rate of 190 kbs.
Basically, I think that AAC may be less forgiving of the source media quality. First impression of course, more tests are needed. Maybe the older CD drive was the only problem here! The difference in perceptual sound quality between bitrates of 128 to 190 kbs from a good source seems to be minimal though, compared to mp3.
A bit of a status update on my poor playback of AAC music downloaded
from the iTunes Music Store... Some tracks sound very bad when played
in iTunes, which I thought might be since I hadn't installed the
QuickTime 6.2 update yet. Nope. Installed it, restarted, same problems.
However, when I burned the tracks to CD, they played flawlessly off the
CD. Something ain't quite right with the AAC playback, I guess...
-- Jarod W.
The reader that originally reported the quality problem replied to another reader's mail asking if the CD was scratched (thinking that may have been a factor).
Thanks for posting that,
this is definitely not the case since it makes no difference what the
format of the original is. i can record direct onto the hard disk and
it still does, use an already encoded mp3 and it does.
but, i have new information!!!
encoding through iTunes gives the beeps. encoding with QT pro gives the
in QT if i select encoding quality Best instead of better, i don't get
the beeps. all other settings don't matter, this one does! now this is
great, i can finally encode a song in AAC.
But, i still can't encode with iTunes, because iTunes has no setting
for best, better, etc.... =(
very weird anyway, since no else has complained of this problem...
I have the same iBook model as James, who had the problem encoding AAC
files. I had no problems creating AAC files. What I might suggest for
him is to use the QuickTime Player application (QuickTime Pro required)
to rip the tracks into AIFF format, check the AIFF files to make sure
they're okay, then import the AIFF files into iTunes 4, select the AIFF
files in iTunes, and select "Advanced, Convert selection to AAC". Then
he can erase the AIFF files from iTunes, leaving the AAC files. This
will isolate if this is a ripping problem or an encoding problem.
Just read your trouble with Itunes 4 ripping, and the same happened to
me. I may be pushing it by ripping on a B&W 350. I noticed the CPU
usage stayed just a few % below 100%!
Maybe slower G3's just can't keep up and the noises are errors. You'd
think there would be a throughput check and a throttle like on CD
burns, if it has to maintain a certain stream speed. It still tries to
rip at 3x and chokes. I'd rather be able to set it to 1x or 2x and not
have to check and repeat the rips.
I also had it quitting on me after about 1 or two tracks ripped off a
CD. I have a pile of CD waiting for AAC and this is a bummer.
Let me know what you find out.
Thanks! - Paul B
This was Jarod's first report - see his later one above also.
Mike, I've had some pretty bad experiences so far. I purchased and downloaded
about $50 worth of music last night, and there are several tracks with
very noticeable audio anomalies. Within the first 30 seconds of one
song, there is a very steep decline in volume, which I KNOW isn't
supposed to be there. A number of other songs have similar,
less-noticeable dips. Other tracks seem to waver from stereo to mono
and back to stereo over brief sections.
I haven't tried encoding any of my own just yet, these are all direct
from Apple. Not sure if it is a function of bad downloads (I'm on cable
though, and the bulk of tracks are fine), bad encoding, bad source, or
a problem with AAC...Jarod W.
I have also experienced problems with Itunes 4 and QT6.2
some sound files soundlike they are moving from left to right and some seem to lose mid-range sound. I looked at the eq display and could see the volume of the mids dropping off the graph. It's very annoying. I'm trying to see if there is a difference between the mp3's I rippped using an old iTunes 2 on OS 9 vs the newer ones I did in iTunes 3 on X.
Your reader with this problem may have a scratched cd. I noticed that
when ripping mp3s that, if the cd was scratched, I would get these
weird sounds (yes, like out of space invaders). The fix was to run the
cds threw a cleaning device such as this one http://www.skipdoctor.com/
I use this product and can attest to its effectiveness. Another
effect of this is increased reflectivity on the data side of the CD,
which leads to increased read times.
To sum up: The space invader sounds are more than likely a result of
ripping from a damaged cd. Solution: Fix the cd.
Note: CD's with scratches that are visible on both the top and bottom
of a cd usually cannot be repaired.
I sent Chris's comments to James, but he noted that was not the issue.
(First Comments from Tuesday's news follows)
"just thought i'd relay my problem with QT 6.2/iTunes4, since it can't help to at least know one person has a problem
downloaded QT 6.2, iTunes4. restarted. all ready to rip some keen AAC i
wanted to do a simple listening test between 128kbs AAC and 160kbs AAC. what i found was a real disapointment. AAC sounds good, except, well... i get tones that sound like something out of space invaders. they seem to be at random, i can encode the same track twice and they are in a different place, seems in the left channel, sometimes the right.
this happens if i export out of quicktime too.
i have repaired permissions. deleted prefs. no joy.
feel my pain, and maybe, others can find a solution. i just feel a bit
alone because no one else has reported this problem.
If anyone else is seeing this or has a suggest, let me know. (As I noted in yesterday's news, I run repair permissions after every X update and it did repair/correct some permissions for iTunes after the v4 update, but that doesn't seem to be a factor in James' problem.) I've not personally done any AAC encoding yet , but the quality of the apple music store samples seems very good to my ears. Here's a reader's comments from the forum:
I did some very quick n dirty comparisons last night. I have decent speakers (Altec 641's) and I was comparing 160kVBR mp3 vs. AAC at 128k. Only with a Natalie Merchant (Ophelia) CD. They really sounded quite identical. I was usually playing 20 second snatches back and forth. Obviously, the AAC files were smaller; and that seems to be the key issue.
Too bad we don't have VBR for AAC! (see reader's comments below on this-Mike) Maybe QT 7 and Tunez 5! Or better yet, Panther.
Another reader linked to a comparison of MP3, AAC, and OGG.
A reader sent a comment about AAC/VBR encoding:
I have seen many posts saying: What about VBR AAC? If I'm not much
mistaken, ALL AAC is VBR -- there is no non-VBR option. It's one of the
things that makes it so efficient. See
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