Originally Posted by EliasGwinn
I've just received some very interesting information from an Apple engineer about the operation of iTunes / Core Audio. I'm going to do some testing, and post the conclusions soon.
For now, I just want to let you all know this:
If you are using iTunes 7.0 or higher, it is important to set the sample-rate in AudioMIDI BEFORE OPENING ITUNES. If you have iTunes open, close it, then set the sample-rate in AudioMIDI. Apparently iTunes locks to the sample-rate that is set in AudioMIDI when iTunes is launched, and the sample-rate can not be changed until iTunes is closed and re-launched.
Elias, others;
Ok here is how it works as I just tested this again.
If you set the Fs rate in the Audio pane of the Audio Midi Setup to say 96k. Then you start iTunes and play then CoreAudio is told to upsample from 44.1 to 96k.
If you go into Audio Midi Setup during your iTunes session and reset this to something (like 44.1) else then it will follow.
You don't have to leave iTunes to change the sampling rate.
Therefore say if you are playing Red book stuff but then want to play high rez stuff, keep iTunes and Audio Midi Setup up and change the rate according to the needs of the track.
As for quality of the upsampling got me, I am not one for mucking with the data.
Test Setup: G5 Dual ---->USB Analyzer-->DAC--->Test System
I used for the dac both my Crimson and the Benchmark both had the same results.
With the USB Analyzer I can easily tell what the Fs rate is by the amount of data sent per frame @ 1ms.
Thanks
Gordon