You should expect to see about 100kbps for G.722 for each direction on each leg. There is quite a lot of overhead on RTP.
How are you measuring bandwidth? At normal 20ms packet intervals, 20 kbps is probably totally unusable for SIP/RTP.
There is certainly no place that would limit bandwidth to such a low figure, unless your network was drastically overloaded, or you are trying to run VoIP over V.34 modem. In any case, the OS would not be setting the limit, and nor would Asterisk or FreePBX.
The call recording sounds much better, almost perfect! We tried it using a softphone with a Jabra headset and a Fanvil 6XU. With the softphones, it sounded better than with the Fanvil. With the Fanvil, we got the feeling that some of the frequencies were being cut off.
However, with both options, we felt that there was less “data” than we expected. We had the Panasonic NS1000 for many years, and the sound was great. We were told not to expect such quality, but it still sounds odd to us