Ever since I have upgraded from Catalyst 12.4 (I tried 12.6 Beta, 12.6, 12.7 Beta, 12.8) I had problem with getting HDMI audio to work properly. Whenever I switched to single HDMI display, after few seconds HDMI audio became VERY quiet (it is audible if I pump volume on my AVR up to +10db, while usually sitting in -20db - -30db range). Odd was, it sometimes was not happening.
2 weeks ago I had GPU-Z running and some music playing, when I switched from my DVI monitor to HDMI (which changed also my default audio device from usb dac to hdmi). While on hdmi output, music played for several seconds more (on AVR, player switched output as default sound device changed), and then went silent. It happend exactly at the same moment as my HD7970 went to low-power mode (150MHz core clock, 300MHz mem clock) as I observed it on GPU-Z.
I did some testing, which confirmed my observation - as long as I kept my cards clock above 150/300, sound worked fine all the time. I tried keeping some 3D application up, using hardware accelerated video decoder, and even keeping 2 displays active up - all worked fine, keeping clocks above 150/300, but it was not really convinient for every day use.
After poking around, I found this file:
At end of xml there is frgment:
<Property name="Want_0" value="15000" />
<Property name="Want_1" value="112500" />
<Property name="Want" value="20" />
<Property name="Want_0" value="30000" />
<Property name="Want_1" value="157500" />
Guess what? Those "Want_0" and "Want_1" numbers correspond exactly to my low power and high power clocks (I have card overclocked to 1125MHz core and 1575MHz mem)! I changed Want_0 values to 50000 and 100000 (500MHz core, 1000MHz mem), and now in low power mode my card operates at those levels, and hdmi audio work fine all the time without any other tricks .
Hope somebody find this useful.