Does This Present A Problem?

I believe it doesn't matter. I do not know the exact science behind it, but I experienced no problems with my own setup, and that includes playback of files of various sample frequencies.

To explain:

I don't use my Mac's built-in sound card, I use an external one. A Focusrite Saffire PRO 40, which is used for recording with multiple microphones in my home studio.

I have it set to a fixed sample frequency of 48 kHz, because that's what I use the most.

I watch movies with this sound card too, which are mostly 48 kHz. However, I also listen to lots of music from iTunes and Spotify, which is all in 44.1.

Judging from this I assume Core Audio has real-time sample rate conversion built-in.

EDIT: Works the other way around too. Movies and YouTube videos are almost always 48 kHz because well, it's film. Your sound card set to 44.1 plays back just fine!

Also, there is one very obvious artifact of "wrong sample rate" playback: you will here a strange speed and pitch adjustment! You'll know when you hear it, cause it sounds weird as hell.

leerkeller said:

About 150 of 9122 of my songs in itunes have a 48 khz sample rate (as opposed to 44.1 khz). I had previously assumed that itunes or the computer would automatically change the output settings to 48 khz when those songs were played, but that is not the case.....

Click to expand...

You are correct. The setting is not changed. What happens is that iTunes re-samples the song in real time. You can avoid the re-sampling by changing the setting by hand but that is a hassle and I doubt you'd notice the difference in the sound.

Nothing to worry about, but if it bugs you then you could always convert those 150 songs to 44.1 in iTunes so that everything matches up....