On the second step of Fast Text to MP3 wizard you should select the Speech synthesizers parameters. Select Speech synthesizer from pull down list of speech engines installed on your computer. Set speed and pitch for selected synthesizer. Press "Test" button to test current voice. If you do not like a voice that change its speed or pitch, or choose other voice from pull down list..
Fast Text to MP3 supports all sapi4 and sapi5 speech engines. If to you do not like available voices you can install better speech engines from Internet.
After selecting voice parameters press "Next" button.