X-Plane uses Windows “Text to Speech” engine to generate the ATIS voice If you here X-Plane sounds and not ATIS, please follow the steps below:
On Windows 7 thru 8.1, Press the "Windows" key on your physical keyboard. This is located between the CTRL and ALT on the bottom left side of the keyboard and type “text to Speech” in the search bar,and select “Text to Speech Settings”.
In Windows 10, you will have to navigate to Control Panel\All Control Panel Items\Speech Recognition\ and select Text to Speech on the left side of the window.
Once in the settings, select “Output” and select your preferred audio device for ATIS.