Explain this

I have this computer running on Windows 98SE. I have FS9 installed, and running Ok. Lately, I updated to Windows Xp Professional. Reinstalled DirectX9, and ran FS9. First impression, My frame rates appear better as well as overall engine sound. The surprice was to hear ATC and pilot. Everybody sounds like they have inhaled helium>>> High pitch voices. Even the morse ID code sounds one octave higher. Just in case, I checked sound producing stuff ( Cd playing) ,, Normal .
Explain this.
Bob
Explain this.
Bob