Continuing the saga of iTunes 7.5 performance issues, it appears there are explanations for it all. In addition, benchmark Media has two suggestions for configuring OS X Audio MIDI. Here is a snippet from Stereophile.
This week, we hear again from Benchmark: Elias Gwinn clarifies what he describes as Siau's "initial observations based on preliminary testing." Gwinn writes, "After extensive testing and communicating directly with the engineering team at Apple, some of these initial observations have been explained. We now know the reason for the poor performance observed in the initial tests, and we have conclusive information about the operation of iTunes 7.x on Mac OS X."
We are suggesting two different recommended solutions to our customers:
"1) The 'Set It And Forget It' solution for iTunes 7.x: Before opening iTunes, set the sample rate of CoreAudio (in AudioMIDI Setup) to 96kHz. Do not change the sample rate of CoreAudio unless iTunes is restarted after the change is made. This solution will prevent CoreAudio from applying SRC, as the quality of CoreAudio’s SRC is horrible. Also, by having iTunes locked at 96kHz, all audio with sample rates below 96kHz will be up-sampled to 96kHz. This will cause virtually no loss in sonic quality, as the quality of iTunes’ SRC is very good—virtually inaudible. Also, by avoiding down-sampling by iTunes, this setting will never result in a loss of bandwidth. " Get the full story here.