The NVidia HDMI ALSA device, present on recent hardware when the nvidia driver is used, is not properly used by Pulseaudio. You need to use hw:NVidia,7 (I think Pulseaudio uses hw:NVidia,3 by default), the number of channels needs to be configurable (I use six) and Alsamixer control "SPDIF 1" needs to be unmuted. It may also be helpful to lock the sample rate to avoid switching delays. load-module module-alsa-sink device=hw:NVidia,7 channels=6 rate=48000 # This is what I use All this can be done by manually specifying alsa-sink and unmuteing the channel but it really should be automatic as more and more users are getting these systems and thus suffer of the problem. The nouveau driver also displays all the same controls but no sound is heard (for now at least), so do not bother trying to use that.
