USB Audio Out Broken on Intel Macs

Yes, the joys of having a Rev. A hardware product from Apple are boundless. My new MacBook Pro seems to have a problem dealing with USB audio output devices. According to a reply I got on Apple’s discussion boards this affects Intel-based iMacs as well.

Thanks to the fact that Apple won’t open the xnu (Mac OS X kernel) sources for the Intel systems, I can’t effectively chase down the issue myself (potentially saving some beleaguered Apple engineer some work rounding up a suitable test rig). So I’ve resorted to filing a bug with the Apple’s developer feedback interface: 4460973 – USB Audio Output Fails on Intel Macs. I’ve never used this before and my previous experience with Apple’s bugfix process was lackluster.

1. plug in a USB audio output device


2. select it for output in System Preferences


3. click Play in iTunes

Feb 25 21:57:09 macbook kernel [0]: USBF: 89320.749 IOUSBPipe[0x4244600]:ClosePipe for address 6, ep 1 had a retain count > 1. Leaking a pipe

I always figured there would be some sort of minor issue like this, being Rev. A hardware and all. On the whole the machine is great, but I imagine this would be a serious bit of sadness for DJ types that weren’t just using the built-in outputs. USB audio output devices work if, and only if, the device was plugged in at boot and the machine hasn’t been in “sleep” mode between then and now. So just reboot, over and over and over again! I’d just as soon leave that fun usability experience to the folks with that other operating system.

It’ll be interesting to see how quick Apple can get a fix for this. Since it affects iMac users as well it’s most likely a problem with the USB controller or the driver for it. However, it’s hard to say for sure without digging a lot deeper, and dig_deeper() is returning ENOXNUSRC.