Stop the Noiz

Apple's Half-Baked Support for DisplayPort

Frank Fox - 2009.01.06 - Tip Jar

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?


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. LEM

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