Audacity is good to use, but tricky. It takes some fidgeting with the program, because Audacity assumes you have to be crazy/stupid to want a file with such little quality.
First things first, you have to set the bitrate of your individual track to 22kHz. Also, make it mono. I've found that if I'm taking a file that already exists and lowering the bitrate, it'll decrease the speed of the sound as a result. If you copy the track, delete it, make it 22kHz, and paste it, that seems to work. It should look like this.
When you export it, you need to pick the file type:
Other Uncompressed Files.
Select
Options and under header, choose a WAV file. For encoding, choose Unsigned 8-bit PCM.