Every digital voice mode covered elsewhere on this site, D-STAR, DMR, System Fusion, lives on VHF and UHF. FreeDV fills a different gap entirely: open-source digital voice on HF, where none of those other modes operate at all.
Open source, top to bottom
Unlike D-STAR’s proprietary AMBE codec or DMR’s commercial ETSI roots, FreeDV is built entirely on open-source codecs, most notably Codec 2, developed specifically to compress voice into a very low bitrate without the licensing restrictions that come with proprietary vocoder chips. That matters if you care about running software you can actually inspect and modify, rather than trusting a closed, patented black box to handle your voice.
How it fits into an SSB signal
FreeDV runs through your existing SSB transceiver using a sound card interface, the same basic setup you’d use for FT8 or PSK31. The software encodes your voice into a digital signal shaped to fit within a standard SSB channel, and modes like the newer 2020 profile can deliver noticeably clearer audio than analog SSB in marginal conditions, at the cost of a harsher-sounding failure mode when the signal drops out entirely.
Why it hasn’t caught on more widely
FreeDV activity remains niche compared to analog SSB or even FT8, mostly because the audience willing to run a somewhat fiddly software chain for HF digital voice is small, and there’s no dedicated FreeDV hardware the way there’s a dedicated D-STAR or DMR radio. Still, if you’re curious about digital voice on HF and already have a sound card interface set up for other digital modes, FreeDV costs you nothing extra to try, and the FreeDV community is active enough to find contacts on a given evening.
Related reading: M17: The Open-Source Alternative to DMR, D-STAR, and YSF · What Is SSTV? · JTDX vs WSJT-X