Getting Audio to work as well as video
The fix is fairly simple, but it might take a few times. What you need to do are flush out your Mac’s PRAM and SMC, resetting them.
Resetting your PRAM is easy:
1) Shut down your Mac totally.
2) Locate (but don’t press) the following keys on your Mac’s keyboard: COmmand, Option, P and R. Put your fingers over them, but don’t press them yet.
3) Turn on your computer.
4) Immediately after turning on your computer, hold down Command+Option+P+R. This must be done before you see the gray boot up screen.
5) Hold down the keys. If you do this correctly, your Mac will restart and you’ll hear the startup sound a second time.
6) Release the keys.
Congrats, your PRAM’s reset! Now let’s reset the SMC for good measure. The instructions on doing this vary from computer to computer, but Apple’s got a great support document that explains how to reset the SMC on any Mac you own.
Once you’ve flushed both the SMC and PRAM, allow your Mac to boot properly. Plug in your Mini DisplayPort or Thunderbolt to HDMI adapter, make sure that HDMI is selected as your Sound output in System Preferences and give your Mac a whirl. Your sound should now hopefully be working through HDMI under OS X Lion. Hoorah!
Using the above steps, I got HDMI sound working on my MacBook Air as well as my girlfriend’s MacBook. How’d it work for you? Let us know in the comments.
By John Brownlee