1.Set the power-off of the display in the power settings.
2.Display of the power is turned off by the setting.
3.The power-on of the display by the return.
4.Then to the speech from the HDMI will not be output.
Display Device Manager are viewing the normal state.
Disable the HDMI audio device from the Device Manager, and then to also be there if that becomes the voice comes out in the enabling.
Disable some cases that is required to reboot when you change there.
Since occur in two environments, the hardware is not a separate problem.
Windows10 + Radeon HD 7870, Windows10 + Radeon HD 7770
Phenomenon in Catalyst 14.12 does not occur.