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Playing iTunes' AAC-encoded music on a PC
Authored by: NetCurl on May 13, '03 03:01:34PM

OK, this may sound like a stupid question, but I need to settle this in my own mind. I have, for quite a long time, encoded my entire music collection (some 300 CDs) to my PowerBook G4. I have *always* used 160kbps, with VBR set to high quality. This, at times, results in larger MP3 files that have varying bit rates ranging from 160kbps to as high as 242 kbps (that's the highest I've seen, but I believe it can be anything greater than 160kbps).

So my question is, I'm thinking of switching to AAC format. This hint solves one of the reasons I wasn't willing to switch (needed to make sure my windows friends could read some of my music), but the second roadblock is quality. Is AAC at 160kbps going to rival my MP3 w/ VBR at 160kbps +?

I've seen plenty of comparisons between AAC and MP3, but I've never seen anyone take into consideration VBR. Can someone enlighten me?



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Playing iTunes' AAC-encoded music on a PC
Authored by: Anonymous on May 13, '03 03:55:37PM

sounds like you're using the iTunes encoder. LAME is much better. use it along with the "Encode with LAME" applescript. i use the "--r3mix" tag which yields high quality VBR encoding.

the problem with your 160k setting is that it sets the minimum encoding rate, which is silly. if you have a stretch of silence, why encode it at 160k/sec?

with LAME and "--r3mix", my files average 160k/sec, but the individual files can range from 100 to 230.

as for AAC encoding, from what i can tell, its not there yet. mp3 encoders have recieved a lot of focus for quite a while and AAC is just now being used as an MP3 alternative.



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Playing iTunes' AAC-encoded music on a PC
Authored by: tc_nyc on May 13, '03 04:23:46PM

That's not totally correct.

A VBR MP3, at least when using LAME, will ignore it's base limit if there is silence. Use the histogram to watch how it encodes an MP3 with a hidden track, so there is a length of silence between the two songs on one track. It will not stick to 160k, but jump down to 32k packets until there is something to encode again. Unless you use the -F flag to "strictly enforce minimum bitrate".

I will agree wholeheartedly that after many MP3/AAC encoder shootouts using LAME 3.93.1 and QuickTime AAC, the LAME still sounds much better. I think the AAC codec has promise and could potentially be much better than MP3, but the QuickTime codec stinks.

But then again, I'd rather have a bigger/badder iPod and just store AIFF files anyway. That's another story altogether.



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Playing iTunes' AAC-encoded music on a PC
Authored by: david-bo on May 16, '03 08:23:32AM

-r3mix is an old setting, not taking the advances of lame in recent years into account. -alt-preset-standard is the current recommandation for lame

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Playing iTunes' AAC-encoded music on a PC
Authored by: carsten on May 13, '03 07:13:20PM
Music encoded with AAC at the same bit rate as an mp3 file will be slightly smaller than an mp3. That is, provided you encode the AAC and MP3 files from the original uncompressed audio source. (Or, if you bump up the quality/bitrate a bit for the AAC file, you'll end up with the same size AAC file as an MP3 but with higher quality/bitrate.)

Note that converting from mp3->aac, or mp3->aiff->acc, mp3->wav->aac or ogg->aac is an utter waste of time, it's like trying to recompress a jpeg: you will lose quality along the way. You need to encode to AAC directly from the original audio CD.

MPEG4-AAC files are always VBR.

To date I have not heard any compression artifacts in any music I compressed with AAC at 128k, but to be safe I re-ripped my absolute favourite CDs at 160k with AAC. Compression artifacts in mp3 files seem to be very common, but that also depends heavily on which mp3 encoder is used (LAME, or Frauenhofer-based enocder etc. etc.)

My listening tests were done with my Harman / Kardon USB digital audio soundsticks with subwoofer; IMHO these speakers achieve an excellent frequency response, with 4 tweeters in each of the L/R speakers, although the sound tends to be unidirectional (as opposed to omnidirectional).

Note that with the QuickTime Player Pro prior to 6.2, you could select a specific (minimum) VBR for MP4 audio pretty much at any bitrate from 8 to 320kbps by holding down a modifier key and dragging the slider. Unfortunately, now with 6.2 you are strictly limited to the evenly powered bitrates in powers of 2 (112, 128, 160, 192 etc.) iTunes 4 also constrains the bitrate selection in this fashion.

DVDs already use AAC to enode the audio track, so for ripping soundclips or music from movie tracks you can probably skip the conversion to AIFF process (but I haven't actually tried this yet.)

I also updated my iPod to the latest firmware and AAC m4a files sound great there too. By re-ripping my CDs as AAC, I'm now saving about 5-10Mb disk space per album as opposed to mp3s of the same bitrate (128k VBR or 160k VBR depending on the album).

So all my ogg files and mp3 files will remain as-is as part of my collection, until I can get my hands on the original CDs to reencode them as AAC.

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Playing iTunes' AAC-encoded music on a PC
Authored by: toddsnc on May 14, '03 09:05:03AM
Frauenhofer (the default iTunes MP3 encoder) clips @ 16K Hz for "psycho-acoustic reasons," meaning very few people can hear frequencies above that. it also saves space as a lot of information is being dropped in the fastest-changing waveforms.

For people with vintage 1990 computer speakers (or laptop speakers) this is probably fine, but newer speakers are much better at reproducing the entire audio spectrum (typically 20-20K Hz) and some people can hear them while many others can feel them to some degree, or at least have some vague feeling something is missing. You can fire up a program like amadeus, open a spectrum analyzer window and watch the sound.

LAME typically encodes the entire frequency range (20-20K) and produces sonically superior MP3s. AAC appears to do the same, with much lower CPU overhead (anyone who's used the LAME plug-in for iTunes knows what I mean). There's no reason not to use the AAC format, except of course that you have to pay for QT Pro.

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