sharing a possible solution I found:
encountered audio problem for youtube nov-dec 2013
for W7 x32
on the lower right side of the task bar, right click on the volume icon, click
click on the Playback tab
check if the playback device is Default Communication Device or a Third Party
device (i have Digital Power Station as 3rd Party)
highlight the built-in sound device (i have IDT High Def Audio CODEC), click the "Set as Default" button....
check all volume sliders / controls just to see if they are set to mute, untick/uncheck if they are... adjust volume to desired level.
* I still wanted to use DPS so I just reenabled it..
* I used a suggested registry edit from another site
* I updated Flash Player
* either one or all of these might have something to do for the fix..
i hope this helps..