I have ripped each of my CDs using the Apple Lossless Format within iTunes. I don't want to keep all these large files in my library, but want to transcode them into AAC files and keep the lossless for if I never need them again. What options should I set for optimal settings within iTunes for my encoding bitrate? I know Apple/EMI is going to release DRM-free AAC files @ 256 kbps - is that would I should also encode all my tracks to? I have an 8 GB iPod nano, but I'm also looking at getting a larger iPod later in the year...

Here are the AAC encoding options within iTunes...

Stereo Bit Rate: 256 kbps
Sample Rate: (auto - default)
> 44.100 kHz
> 48.000 kHz
Channels: (auto - default)
> Mono
> Stereo
[] Use Variable Bit Rate Encoding (VBR)

thoughts? comments? and/or suggestions?

Generally, AAC is transparent at 160 kb/s, but it could be higher or lower depending on how well you can hear. You should do some ABX'ing to determine the lowest bitrate that's transparent to you and use that. (It's probably much lower than 256 kb/s.)

so if I transcoded my lossless into 160 kbps AAC files (CBR, not VBR) then I'd be set?

VBR is usually recommended over CBR. Don't take 160kbps as fixed and set, rather do the experiment yourself and try a double blind ABX test with different bitrates - use music you listen to most of the time. You might be surprised how low the needed bitrate really is! That means you can fit more of that music on the iPod =)

how does vbr differ from cbr? I know file sizes are smaller, but doesn't it make the sound less?

vbr @ 160 kbps doesn't sound as good as a cbr @ 160 kbps, or are they "equal"?

You had better come up with some blind ABX results before you post something like that.

Normally, anytime a encoder offers VBR encoding, you use it. VBR stands for variable bitrate. Many encoders like iTunes AAC, Lame mp3, Nero AAC, and Microsoft WMA all support VBR encoding. Although many people think that the iTunes VBR AAC encoder is more of a quasi-ABR encoder, it still does a decent job. The way the iTunes AAC encoder works is that you pick a bitrate (say 160kbps) and you enable the VBR encoding. iTunes will then encode a song in which the bitrate will not drop below 160kbps. However, during complex parts of the song, the bitrate can actually increase beyond 160kbps. I have some 128kbps VBR iTunes AAC files and their overall average bitrate actually came out to around 154kbps, so the bitrate can increase way beyond its selected target bitrate.

More than likely, you suffered from the placebo affect in that you think VBR is worse than CBR so your ears heard that. Download a program called foobar2000 and conduct a blind ABX test. You will probably surprise yourself to find out that you will probably have a hard time even hearing the differences between 128kbps VBR AAC and the source lossless file.

I really think high bitrates are over rated. There are actually some people (most of them are members of this board) who can hear a difference between 256kbps AAC and the source lossless file or even 128kbps AAC and the source lossless file. However, the audio world (have a look at the forums on iLounge) is mainly filled with people who think they can hear a difference so they want to encode their audio at the highest bitrate possible. Or they have the mindset that VBR is worse than CBR so they will fight VBR to the death.

The number one rule in audio encoding is to go with your ears. Don't fool yourself into believing that CBR is better than VBR or that 256kbps is better than 160kbps. If you can hear a difference when conducting a blind ABX test then go with your results. Don't choose your bitrate/format based on what other people say. After all, you will be the one listening to your music.

Not with iTunes they aren't smaller - at least not necessarily. What seems to happen is that the iTunes encoder (which is, presumably, the Core Audio one) takes the nominal bitrate as a "floor". If the sound is complex enough to need it, the encoder bumps the bitrate up. You can end up files that have an average bitrate slightly lower than the nominal bitrate, but not by much. They're more likely to end up with an average bitrate a little, on occasion a fair bit, higher.



No, it sounds better. With VBR set the resulting file will use more bits if necessary, where it needs to, and will therefore sound better. Whether the difference is audible to any given listener is another matter.

The iTunes encoder is a little lacking in flexibility, though. As you probably know, with some VBR encoders, e.g., the LAME MP3 encoder, there is no nominal bitrate. You select a quality level instead. The resulting average bitrate of the file can very quite a bit, because it depends on the characteristics of the track/s you're encoding. If you had some old mono recordings on a CD you were ripping then LAME might encode them at less than 100kbps; if you had some particularly demanding tracks to encode LAME might go up over 200kbps, and this is on the same setting. The iTunes encoder is not like this at all.

It is using a more modern format, but it 's not using it very flexibly. Even if you use VBR, you're likely to end up with a files that have roughly the same average bitrate irrespective of the encoding demands of the track. So you stand to either waste bits where they're not needed, or on the other hand not have enough of them where you might. On your computer, this probably doesn't matter, because you can err on the large filesize and not worry about the wasted space. On a portable player, even though hard drive sizes have gone up over the last few years, you'll be losing hard drive space where there's less of it to spare. With higher bitrate files, you'll also be working your player harder than need be and, therefore, running down its battery faster than you need to.

If you're on Windows you might look at Nero's AAC encoder, too. I haven't used it myself: I'm a Mac guy. But you can set it to a quality level - the default is 0.5 - and I'd suspect it may well deliver you files that are better optimized for quality vs. filesize.

Does the ipod have any problems with VBR AAC files like it has problems with VBR mp3 files?

Not at all. In fact, those VBR mp3 issues have been fixed in the 5G/5.5G iPod models. Basically, the older generation iPods were having trouble keeping up with a drastic bitrate change in a song. If the bitrate in a song went from 128kbps then sharply increased to 256kbps or even 320kbps, the iPod would introduce a small audible pause as the processor had to be throttled up to handle the higher bitrate music. This is not the case for new iPods.

In fact, the 5G/5.5G iPods can now playback iTunes AAC (VBR/CBR), Lame mp3 (CBR/VBR/ABR) and even Nero AAC (VBR/CBR/ABR) files gaplessly. When gapless playback was added to the 5G/5.5G iPod models, it only supported the gapless playback of iTunes AAC, Lame mp3, FhG mp3, iTunes mp3, or Apple lossless files. Apple released a slightly newer version of iTunes that now supports gapless playback of Nero AAC files and the 5G/5.5G iPods support them as well.

All in all, any playback functionalities that existed in the older models (sound quality and format support aside) are now gone. I can't vouch for the 2G iPod shuffle or 2G iPod nanos if they can handle Lame VBR mp3 without and problems but I don't see why they would have problems especially since they use flash based memory.

2G iPod nano's handle LAME VBR just fine. In fact, the 1G nano's do too if you have the latest firmware.

Don't know about the shuffles, although it is doubtful that many people will have VBR MP3's on a shuffle due to file size issues.

do whatever your heart desires! (but you're better off doing the AB thing.)

i dumped AAC in favor of LAME V2 because MP3 is universal. the company cars can read an MP3 CD. i'd guess rental car CD players can read MP3 CDs. i can give a friend an evaluation song in MP3 & know he can play it.