You just started to play your game (possibly Metro 2033) and saw the error pop up about X3DAudio1_7.dll is missing. This error is about Microsoft’s DirectX missing a few required files. All you need is a simple update, so let’s get straight to the fix.
Head over to Microsoft’s website to download DirectX End-User Runtime. This file will update your DirectX, regardless of what version you have installed. I had this issue on a Windows 7 machine and after the update was applied the error message was gone. On previous versions of Windows, you may need to reboot.