This year at Rocky Mountain Audiofest I received a call from a manufacturer having trouble playing some newly acquired 24/88.2 files. He was using a MacBook with OS X Leopard 10.5.5 and a 24-bit USB interface. Every twenty to thirty seconds during playback there was an audible glitch. I offered my MacBook Air with OS X 10.5.5 and we heard the exact same problem. After about forty-five minutes of testing every configuration known to man we could not get 24/88.2 material to playback on OS X without audible errors. PC users will be happy to know Windows XP played the files flawlessly. I talked to the usual suspects around the show and sent a couple emails searching for answers. No solid information could be found.
As I mentioned earlier we tried for forty-five minutes to get the 24/88.2 material playing without errors. Interestingly enough we did get this material to playback perfectly if we used OS X core Audio to upsample to 24/96 and we succeeded in playing back a 24/96 track downsampled to 24/88.2. To be absolutely sure there wasn't anything wrong with the file we had someone in another location play the same source file on his system. Everything worked perfect. The difference between the working and non-working systems was the interface. Using a Lynx AES16e card the 88.2 material played perfect. Unfortunately there was no 24-bit USB interface available for the offsite person to test.
When I arrived back home in Minneapolis I used the same 24/88.2 music with different interfaces on my Mac Pro. I was able to reproduce the same playback errors using my Benchmark DAC1 Pre via USB. Some commonalities between the systems were Mac OS X, USB interfaces, and CEntrance chips. After a few days it was determined that the Mac OS X USB driver was the culprit. Apple was said to be working on the issue and a couple weeks ago I was told the issue had been resolved by Apple but the release date of the patch was unknown. Last night when OS X version 10.5.6 was released the first thing I did was test the USB interface with 24/88.2 material and voila (vwä-?lä) everything was perfect. I could not get the system to hiccup no matter how long I played 24/88.2 material.
If anyone has OS X version 10.5.5, some 24/88.2 material, and a 24-bit USB DAC it would be great if you could reproduce the playback problem. Then update to OS X 10.5.6 and let us know if the problem has been resolved in your system.