HF Digital Voice /FreeDV
https://www.youtube.com/watch?v=XUizi2W1LTk (Comparison of digital voice modes for maateur radio)
FreeDV:
https://freedv.org/
https://ei7gl.blogspot.com/2019/11/freedv-digital-voice-mode-for-hf-bands.html
https://github.com/drowe67/freedv-gui/releases/