Workaround for audio problems with OS X 10.6.8 update
A number of people have run into audio problems after installing the latest OS X 10.6.8 update. While a true fix will have to come from Apple, here is a workaround that may help some people.
So far the prevalent issues that have cropped up for the OS X 10.6.8 update have been an inability to print with some printers, and some incompatibilities with a few popular programs that have cause some system-wide issues for people using those tools (crashes and high CPU usage). In addition, another problem that has cropped up is various audio problems including no audio, and audio cutting out after a period of playback.
As with the printer problems, the current audio issue appears to be a problem with an updated system file, namely the AppleHDA (High Definition Audio) kernel extension. The quick workaround for now if you are experiencing audio problems is to revert to a previous version of the kernel extension in hope that it restores audio functionality again.
To do this, you will need a Time Machine backup of OS X, and then follow this procedure:
Go to the /Macintosh HD/System/Library/Extensions/ folder.
Invoke Time Machine and migrate back to a time before you installed OS X 10.6.8.
Select the "AppleHDA.kext" file in the Time Machine backup.
Restore the file, replacing the one in your current folder.
Alternately, you should be able to accomplish the same task by downloading the OS X 10.6.7 Combo updater and extracting the included HDA kernel extension from there. To do this, download the updater in addition to the package management tool Pacifist, and follow these instructions:
Double-click the 10.6.7 combo disk image to mount it, and open Pacifist (wait 15 seconds for the registration request if you have an unregistered version).
Open the updater package on the disk image with Pacifist.
Navigate to the "AppleHDA.kext" file in the updater, which is in the following location:
Contents of MacOSXUpdCombo10.6.7.pkg > Contents of Manual > Contents of MacOSXUpdCombo10.6.7.pkg > System > Library > Extensions
(Alternatively you should be able to search for "AppleHDA" in Pacifist's search bar to locate it.)
Select the "AppleHDA.kext" file in Pacifist and then click "Install" in the toolbar.
After this is done, restart the system and you should be good to go. Since you are restoring from backup the permissions for the file should remain intact, but you can also verify or repair them using Disk Utility as an added step.
This workaround still may not allow full audio functionality, and some more-elaborate audio setups may see no fix at all; however, people who are experiencing audio drop-outs and other odd problems with basic setups have seen the problem fixed by reverting to the prior version of the kernel extension.