Tech Question: Sound through HDMI

[wwenze]

HDMI has enough bandwidth to send multichannel uncompressed. Which is what the audio controller will be generating when doing normal stuff like watching YouTube and playing games.

The only time where it will be sending DTS or DD would be when you play DD / DTS audio and you select pass through. When you do that, all other sounds on your computer will be disabled when the program has control.

There is a third scenario of generating uncompressed and converting them to DD or DTS on the fly, called Dolby Digital Live or DTS Connect respectively. But this was only relevant in the SPDIF days which has insufficient bandwidth for multichannel uncompressed. Most GPU don't come with this capability since it requires licensing cost.

 

[Kiwi8]

On a side note, I wonder what happens if a HDMI GPU card is installed in a motherboard that does not have integrated sound chip (those very old motherboards).

Does it still process the sound that's output via HDMI port?

 

[wwenze]

On a side note, I wonder what happens if a HDMI GPU card is installed in a motherboard that does not have integrated sound chip (those very old motherboards).

Does it still process the sound that's output via HDMI port?

Yes.

If you look in device manager, the integrated sound has its own device ID (usually with a vendor id 8086 = Intel), the GPU sound has its own device ID (1002 for vendor AMD)

 

[Alphas]

A way to view the different format of audio data is to take DTS as red boxes, DD as green boxes and PCM as blue boxes. These data comes from a source such as a movie and the audio data can either go to the GPU or sound card or motherboard audio controller.

The audio controller then convert the data to SPDIF, it is a transport signal and let say its a van where the boxes are loaded. It can either pass through the HDMI, optical, or coxial, just like how the van can take different routes to the destination. However the van cannot change the box colour, so green box cannot become a red box etc. That's where the sound card or some motherboard audio controller comes in, it can encode multichannels PCM audio to DTS/DDL, so the blue boxes are encoded to become red/green boxes. So far GPU audio controller does not have the capability, maybe in the future. All the data are in the digital domain, so technically there is no loss in quality, until it get decoded to analog sound.