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For context, FreeDV is an SDR system based on Codec2, which is a codec designed to pick up at bitrates lower than where Opus stops being useful, which is about 12kb/s

Codec2 goes up to 'only' 3200b/s. Seems like there's a hole there for open codec between 3kb/s and 6/12kb/s.

That hole is mostly covered by G.729 and AMR-NB.

https://en.wikipedia.org/wiki/G.729

https://en.wikipedia.org/wiki/Adaptive_Multi-Rate_audio_code...

> That hole is mostly covered by G.729 and AMR-NB.

G.729 seems to be open with many/most patents expiring in 2017.

AMR-NB appears to need licensing, so not as open as Codec2 or Opus.

Regardless: if Codec2 could be pulled up and/or Opus pulled down, then most audio applications could do with really only two libraries.

David Rowe's blog at rowetel.com details a lot of the development behind codec2 and is always an interesting read.

It definitely sounds better than AMBE2 in DMR.

DMR's AMBE+2 works reasonably well for English, but certain languages sound as if the speaker was drunk and having a stroke at the same time.

FreeDV – Digital Voice mode for HF radio