For this song I used Whysynth. A DSSI plugin for GNU/Linux.
You can download the high quality audio from the internet archive
For this song I used samples from Kara square and Speck.
You can find them here:
Kara Square: the female voice
http://ccmixter.org/files/mindmapthat/42191
Speck: the male voice
http://ccmixter.org/files/speck/42207
Which are both licenced under cc by-nc
https://creativecommons.org/licenses/by-nc/3.0/
Then I used a sample from Rez Izain where I can't find the source anymore. Sorry