The classical approach is a matched filter. Here's some references: https://www.rfcafe.com/references/articles/wj-tech-notes/fsk-signals-demodulation-v7-5.pdf

The classical approach is a matched filter. Here's some references: https://www.rfcafe.com/references/articles/wj-tech-notes/fsk-signals-demodulation-v7-5.pdf https://www.rfcafe.com/references/articles/wj-tech-notes/fsk... http://edge.rit.edu/content/P09141/public/FSK.pdf http://edge.rit.edu/content/P09141/public/FSK.pdf There's lots of matlab code floating around out there, if you're willing to try gnuradio that'll work (for example: https://nccgroup.github.io/RFTM/fsk_receiver.html https://nccgroup.github.io/RFTM/fsk_receiver.html), and this looks promising: http://www.whence.com/minimodem/ http://www.whence.com/minimodem/ ETA: Audacity might be able to do it too : https://www.youtube.com/watch?v=tKNNnbgoGdI https://www.youtube.com/watch?v=tKNNnbgoGdI