Wednesday, September 23, 2009

Windows 7 ATI HDMI audio vs digital coax audio issue

A few weeks ago, I was in France. I took advantage of the occasion to upgrade my mother's computer to much more recent hardware, as well as her television to a new 46" LG LCD HDTV. The PC was setup with the final version of Windows 7 x64.

She kept her old PC monitor, a 15" LG LCD, with only a VGA connection, as well as her old Yamaha RX-V420RDS amplifier, which long predated HDMI.

The PC sported a Sapphire video card with an ATI Radeon HD4850 chipset and dual DVI outputs. One output went to the 15" LCD with a DVI->VGA adapter, and the other went to the TV with a DVI->HDMI adapter and a 15m HDMI cable.

The PC audio was connected to the digital coaxial input Yamaha amp via a 15m coaxial cable.

After I taught her how to switch back & forth between her 2 displays in Windows 7, my mother noticed a very odd problem : when she was using the TV as her display, all sound disappeared ! But when she switched back to the 15" analog VGA LCD, it came back. I was unable to debug the issue for her over the phone. But I still had some more time before flying back home, and determined the root cause of the problem in person : Windows 7 had seen it fit to automatically redirect all audio to the HDMI output of the video card when the display was switch to the TV !

This was of course not what was desired for her setup. The TV's audio was muted and we had no intention of using its built-in speakers. We wanted the audio to always stay on the digital coax output hooked up to the Yamaha amplifier . I fixed this in the Control Panel by disabling the ATI HDMI audio output device. I hope this will help someone else running into the same issue of lost sound when switching displays.


  1. I'm having a similar issue. The TV has a digital audio output and my motherboard supports input but once I change the TV's input to what I want to hear nothing comes out my 5.1 speakers hooked up to the PC. I'm running HDMI off the nforce 750a though; any suggestions?

  2. There are several solutions with the 750a :
    1) If allowed, in your motherboard's BIOS, you can disable the HDMI audio support. There will be an option for audio CODEC "internal/external". Experiment with the values and you should be able to disable the HDMI port completely. Then Windows shouldn't be able to route the audio there anymore.

    2) If that does not work, go to Control Panel and look for the nVidia HDMI audio device. Double-click it and select "disable". That should also ensure that no audio will be routed there.