Dithering in iTunes?

iTunes does not have any advertised support for 24 bit audio, and although people on this Forum have reported on various experiments, I certainly would not trust iTunes to do the correct thing with 24 bit files.

Also, if you are creating MP3s, iTunes is not a good choice, since it uses a low quality MP3 encoder.

At that level of audio, you would be best off using a high-caliber conversion program, such as dbPoweramp, and then add the resulting MP3s in your iTunes library.

The MP3 encoder can be switched between low quality, high quality and other qualities inbetween. I wouldn't consider iTunes a bad encoder

Compared with any other MP3 codec, iTunes is about the worst there is.
Low, medium and high quality settings are all relative to the codec you are using, not to any standard.

Any reason you are not using AAC instead of MP3?

photonal wrote:
I can play 24bit AIFFs fine in iTunes.

When you look at the conversion options, you will see that it does not offer converting to 24 bit as an option. If you want to see how it does converting from 24 bit, feel free to experiment, but there are way better tools out there.

The MP3 encoder can be switched between low quality, high quality and other qualities inbetween.

The word "quality" in the iTunes MP3 encoding options is used two ways, to refer to the bitrate and to the VBR algorithm. Neither of those means it is not a crummy MP3 encoder.