Apple's Mini DisplayPort
doesn't do audio? What the heck is going on?
How could Apple release a new connector but not support the
audio?
That was the issue raised when an alert reader, Daniel, who let me
know that all the audio for the fancy new Apple LED Cinema Display is being
carried by USB, not the Mini DisplayPort.
The USB Cable
I know that the iSight camera and microphone use USB, because these
are separate from any video and sound input from the computer. But it
didn't make sense that Apple wouldn't use the audio portion of the DisplayPort specification (which
supports up to 8 channels) to handle sound.
I was mystified by this news. To double-check, I searched for
detailed reviews of the LED Cinema Display. I found a review at
Engadget that confirms that sound only started working once USB was
connected.
The DisplayPort Specification
I then searched for the specification
of the Mini DisplayPort and confirmed that all 20 pins are there, just
like the full size DisplayPort connector.
The pins - and presumably the means - for sending sound is there. I
checked on VESA's website to
confirm that audio is supported - it is.
So what the heck is going on? All the pins are there, and the
specification supports audio, so why does Apple send the sound through
USB instead?
Confirmation
I still couldn't believe that Apple would forget to send the sound
through the Mini DisplayPort. Time for me to take a trip to the Apple
Store to confirm the facts for myself.
There was no doubt once I was there. Unplug USB, and the sound goes
back to the computer's internal speakers. I checked the sound control
panel in System Preference, and the only options were internal speakers
or USB speakers.
That finally convinced me that the DisplayPort wasn't handling
audio.
What about other computer vendors? Both
Lenovo and Dell seem to
having similar problems.
The Source of the Problem?
What hit me about the Dell link was the idea that the video card was
the source of the problem. This makes sense, especially for a PC - they
have long had separate video and sound cards. The folks at Nvidia and
ATI/AMD are not sound experts. It's likely that they haven't
incorporated sound on their video cards. Therefore it may not be a
problem with Apple, Dell, or Lenovo, but rather the video cards
themselves that lack audio.
So far no one has claimed responsibility for why the audio is not
being sent via DisplayPort.
While searching for info on the 9600M GT video card used in the new
MacBook, there was a hint of the issue on the Wikipedia page
about the Geforce 9 series video cards. Way down on the list, it talked
about the Geforce 9800 GX2 having a S/PDIF-in connector for
routing audio to the HDMI cable. At least for that card, the audio had
to come from somewhere else to be routed to the HDMI.
The folks at Nvidia and ATI don't have to be sound experts if they
can just pipe the sound in from somewhere else. The question is, why
aren't they doing this audio routing for the DisplayPort
connection?
Unfortunately, that question remains unanswered. It could be that PC
makers, including Apple, aren't ready for it yet, or that the chips
aren't done baking. (Please note that some video cards may have sound
working while similar models don't. My research shows that video card
get modified by different OEMs, e.g., Apple's video cards won't work in
a PC.)
No wonder
there aren't any Mini DisplayPort-to-HDMI converters yet. Any
adapters will need to get the sound separately.
Partial Implementation
Until enough hardware starts using DisplayPort technology, who knows
what the standard configuration is supposed to be? Apple got around
this by releasing its own monitor, a nice solution that hides the
limitation. (Granted, if they had stayed with DVI, audio would still be
separate.)
I'd prefer to have this technology working fully before I buy
anything that uses it - or at least a commitment from computer vendors
to keep things this way for awhile. There's nothing I hate more than
new kit being out of date in six months.
Since I'm not in the market for a MacBook at this time, I'm not too
upset. I just hope they have this resolved by the time the new Mac
minis and iMacs come out.
Somehow I doubt that it will be, and my wait for another computer
will continue. 
