These settings will give you audio quality similar to XWA's radio voices.

Goldwave

Filter-->Low/Highpass
Initial hz:  500
Highpass
Steepness:  5
Static.

Effects-->Resample:11025

File, Save As.  8 bit.  mono.  unsigned.

Cool Edit Pro 2.0
Edit-->Convert Sample Type...
Sample Rate:  11025
Mono
Resolution:  8 bit

Effects, Amplitude, Amplify...
Boost the decible volume to the max level without letting the voice peak out (touch red).
File, Save.