[Ground-station] FreeDV QSO party, FreeDV GUI as a starting point for P4G?

[Phil Karn]

On 2/25/19 14:04, Michelle Thompson wrote:
> 6 kb/s isn't really where I'm looking at for us. We need something more
> like 20 kb/s. The 6kb/s choices still sound bad to me. It's just still
> an inferior experience at 6 kb/s. 

That's fine. 6 kb/s is just the minimum (though I think it's been
lowered to 5); Opus can go all the way up to 510 kb/s though it is
obviously overkill for voice. The point is that it subjectively
outperforms just about every over codec at a given bit rate.

> Opus at 20 kHz bandwidth (I think it's their 40+ kHz sampling rate)
> might fit the bill. If Opus had something higher, then that's even better. 

Bandwidth is just one of the things that Opus varies dynamically
depending on the data rate you give it. It can also shift algorithms
between those optimized for low rate speech and high quality music. I
regularly use Opus at 32 or 16 kb/s to pipe communications receiver
audio around, and it sounds just fine. To make the best use of it, you
should handle variable length packets at fixed intervals. The minimum is
2.5 ms and the maximum is 120 ms, but I typically use 20 ms as a good
compromise between audible latency, CPU scheduling and packet overhead.

Phil