Since discovering 24bit music a few months ago I've been experimenting a bit, including iPod playback. I've stumbled on this thread, and here are some thoughts:
Can an iPod play 24bit FLACs? --no, but my 2nd generation iPod Touch can play 24bit Apple Lossless files. If you have FLAC files, you can convert them using a really nice utility called X Lossless Decoder (XLD) which makes bit perfect conversions from FLAC to Apple Lossless and back again. You can download from here -->
http://tmkk.hp.infoseek.co.jp/xld/index_e.html
Can an iPod play 24bit/96KHz Apple Lossless file? --no, apparently not (at least mine can't) which is something I discovered by accident. It turns out my first 24bit music had a sampling rate of 48KHz, so my iPod swallowed it and played it no problem. Then I got hold of a 24bit/96KHz file and was surprised when iTunes told me that my iPod couldn't play this type of file. The answer is to use XLD to down-sample the 96KHz file to a 48KHz file, and use that copy on your iPod. The full fat 96KHz files play fine in iTunes on your Mac, though, so don't discard them.
Why do I downsample to 48KHz and not 44.1? -- think about it: 48 is half of 96, and 44.1 is not. Half the sampling rate means that (thinking about it in movie terms) every other frame is used without any interpolation (and therefore further degredation) of the original. I have seen 24bit/88.2KHz studio master files for sale on some audiophile websites. I haven't tried one yet, so I don't know if these work on an iPod without down-sampling, but again, the answer for me will be to down-sample to 44.1KHz and not 48KHz.
Does it sound better? --oh yes! The first bit of 24bit music I got was a free download 24bit version of a CD I bought. Naturally the first thing I did was to listen to the same bits of music back to back in both losslessly ripped CD (16bit/44.1KHz) and 24bit/48KHz and the difference is astonishing. The first impression is that the 24bit version is less bright than the 16bit version, but very quickly I realised that was because the music had lost that hard digital edge I'd got used to after years of ignoring vinyl for the convenience of CDs. Then I started to notice the extra detail. In one bit of music, the CD version had a vague background huffing noise I couldn't identify except to say it was a bit of studio background noise. On the 24bit version it's unmistakably the depress-release of a piano's sustain pedal. All kinds of detail in the music has become apparent sicne then.
OK, so does it sound better on an iPod? --absolutely! 24 bit sound is vastly better than anything you've heard on an iPod but you've got to upgrade your iPod a little. The player itself is really very good and worth every penny and then some. The negative value left over is in those tinny little headphones Apple insist on supplying, which for years, and through various generations of iPod/Phone I've owned have gone in the bin without even being unwrapped. Hateful things they are -- just get rid of them! Right now I use Shure SE-530 in-ear headphones, which were very good anyway, but since my discovery of 24bit music have really come into their own. These are expensive though, at roughly twice the price of your average iPod, but there are definitely cheaper alternatives that will massively improve your listening experience. The key is to isolate as much noise as possible (isolate, not "noise-cancel" which in my experience doesn anything but that) so if you don't like stuff shoved into your ear canal, a decent quality chunky pair of retro style big ear pad headphones would serve you well I reckon.
What else have I tried? --well, I've discovered that 24bit files made from vinyl originals sould a lot like vinyl originals in both good and bad ways. The characteristic vinyl rumble and crackle is faithfully preserved in 24bit/96KHz form... Secondly, 24bit files ripped from a digital source such as SACD or DVD-A sound amazing. Thirdly, AAC (which is NOT AT ALL LOSSLESS) is far worse than a losslessly ripped CD, so STOP PAYING APPLE FULL PRICE FOR A LOSSY FILE IN THE iTUNES STORE. Whilst I love Apple, this is one area where they are pulling a fast one on all of us. Tell them it's unacceptable, and go back to buying CDs from Amazon until they at least give us the option to buy lossless versions of the music. Finally, MP3 files (God help your ears if you still have some of those) are vastly worse even than AAC files. Lossy compression is bad, and old style lossy compression is the worst of all.
What do I still want to know? --lots of stuff generally, but in relation to this, here are a some questions that still bug me:
* why don't record companies make 24bit music more widely available? Why are we confined to very obscure music offered only on specialist audiophile websites? SACDs and DVD-As are out there, and most self-respecting recording studios these days oftem make 24bit/192KHz masters. Why make the best thing generally available for us to listen to down-sampled and degraded 16bit/44.1KHz versions on a more than 3-decade old physical format? (Answers to this question that involve the word "copyright" will be redirected to /dev/null by the way, on the grounds that they are very boring indeed)
* what is the highest spec Apple Lossless file that an iPod will play? So far I know only that 24bit/44.1KHz and 24bit/48KHz work, and one of these days when I have time, I'll down-sample a 24bit/96KHz file to 24bit/72KHz and 24bit/88.2KHz and see where iTunes stops uploading it to my iPod. If and when I know, I'll let you know.
* why don't Apple publish a proper specification of what kind of Apple Lossless file any given iPod model will play? The second I see "Apple Lossless up to 24bit/96KHz" or better I'll upgrade -- Apple, that's a promise.
