Just in passing, I mention that ever since late last year (around November 2018?) the version of nVidia drivers for Quadro (notebook) "broke" HDMi audio going out to external monitors and HDTV's, at least on several Lenovo Thinkpad models that contained a BIOS option for "discrete graphics" (i.e. 100% nVidia GPU and 0% Intel HD Graphics, for both laptop screen as well as DP/HDMI externally connected displays).
The issue was than when operating in "discrete graphics" mode (as opposed to the "hybrid graphics" alternative, a.k.a. Optimus mode, where the Intel HD Graphics supported the laptop screen and nVidia GPU supported exteraal displays, with the nVidia GPU "helping out" on the laptop screen when more GPU horsepower was required for certain apps or situations) physically connecting the external display caused the HD Audio Device driver object to actually disappear in Device Manager. This forced the use of the laptop Realtek HD Audio and built-in analog speakers rather than sending digital audio out over the DP/HDMI cable to the external monitor or HDTV.
This symptom (which was present for both Win7 and Win10) had never been present before with nVidia graphics driver 392.00 and older. But with every graphics driver newer than 392.00, this symptom was present. And it's been this way for the past 4-5 months, with nVidia blaming Lenovo and Lenovo blaming nVidia. Again, there was NEVER a problem with 392.00 and older drivers and exactly the same laptop BIOS implementation of "discrete graphics". But if you installed any driver newer than 392.00, bingo... loss of digital HDMI audio.
Well, after much finger pointing, and Lenovo finally deciding they should fix something in their BIOS for "discrete graphics" (which I've been told by Lenovo engineering will be officially released in the next few weeks at least for their P50/P70 laptops), completely unannounced it turns out nVidia appears to have also fixed their 430.39 driver to somehow get things back exactly to how they worked (i.e. perfectly!) with 392.00 and older.
So whatever they broke right after 392.00 and never realized they broke it, they've now fixed it so that HDMI audio now once again works perfectly, starting with 430.39. And this fixed result occurs with 430.39, even with the untouched current BIOS in the Thinkpad laptops still running the same "discrete graphics" logic. Doesn't seem that the upcoming Lenovo BIOS fixes are needed now, but apparently Lenovo is going ahead with their change anyway. Hopefully things will stay fixed with BOTH changes in effect soon, i.e. both Lenovo BIOS fix for "discrete graphics" and nVidia driver correction now present in 430.39 and newer. Fingers crossed nothing gets re-broken.
I had this problem with both my Thinkpad W530 (Quadro K1000m nVidia GPU) and P70 (Quadro M3000M nVidia GPU) laptops, both of which support "discrete graphics" in their BIOS. Again, "discrete graphics" allocates the nVidia GPU not only 100% for external displays, but also 100% for the laptop screen. Intel HD Graphics is totally disabled. But now that I've installed 430.39 on both laptops, sure enough HDMI audio is now once again working perfectly out to external displays over DP/HDMI cable.
