G.722-HD codec not working for outgoing calls via Fritzbox

I use Jitsi 2.10.5550 on Windows 10 as SIP client to a Fritzbox 7490. The Fritzbox can handle G722-HD codec. After enabling G722 codec in Jitsi the codec is used, but the sound is terrible.

I searched the internet and the solution recommended on several forums is to disable G722 in Jitsi - that works, but unfortunatelly then the call is in lower audio quality.
In the forum the same problem was already mentioned in year 2012 - (Jitsi call on G722 via Fritzbox grunts like a pig
[jitsi-dev] Re: Jitsi call on G722 via Fritzbox grunts like a pig) and in 2015 ([jitsi-users] Codec G722), but no final solution was provided.

Maybe the problem is that eventually Jitsi uses two codecs in parallel. Fritzbox Log states G.711u, G.722-HD (both!) for outgoing (Jitsi) and G.722-HD for ingoing (internal answering machine), while in other logs only one codec is listed for outgoing and ingoing. Using other softphones with G.722-HD causes no problems.

Any chance for a solution?

Regards,
Ulrich