switch 1.1.2 mac, and win
http://www.ralcr.com/switch_tests/
open the html's. you can see the same song converted on a mac, and on a pc. first is playing faster, the second is playing normal. both at 56kps.
i hate to run windows even for a small job like this. i don't know what converters exists for mac but i tryed another one that has poor quality with the same bitrate.