What does "PBX Delivers audio" EXACTLY do...?

[YiannisH_3CX]

To provide a better answer i might need some additional information about the installation and setup.
You mentioned that the PBX is hosted by the provider so how are the phones provisioned to the PBX? You mentioned Snom phones but what are the models used?
Also what is the codec priority under extensions settings?

 

[FredyWenger]

2 x Snom d345, provisioned on 3cx over a SBC.
Codecs: G.722, G711A, G711U (the same config and order to all extensions and also to the SIP trunk config on the 3cx).
As I wrote, the voice quality is good in internal calls (only one stream with G.722), but very bad, if the SIP trunk is involved (although G.722 ist used for all three streams according to the trace).
I could imagine, that - maybe - the streams are transcoded "in the background" on the SIP trunk multiple times, what I can't see in the trace (e.g. in: G.722 -> SIP trunk -> G.711A / what ever) -> out: G.722).
This way I only see G.722, but the result (what I hear) was transcoded underway (may be multiple times) to a worse codec.
But, I have no idea if this can be or not...

 

[YiannisH_3CX]

OK, run the following test and let me know of the results. Navigate to the extension settings for both extensions / Phone provisioning and leave only G722 as the available codec and also re-enable the PBX delivers audio option. Reboot the phones so the new settings are applied and make a call between extensions. Let me know if the audio quality is OK.
Also let me know of the build version of the PBX. You can see it on the Dashboard under the Information column.

 

[FredyWenger]

As I wrote, the same codecs in the same order are also configured to the SIP trunk on the 3cx.
Should the SIP trunk also be reconfigured (only leave G.722) for the test or not?

 

[YiannisH_3CX]

This test should be performed with a call between extensions. The provider should not be included in this test. The extensions should only have G722 as assigned codec and PBX delivers Audio must be on.

 

[FredyWenger]

I then don't see the sense of this test...?
As I wrote, internal calls already works correct (only one stream with G.722 and good quality).
So.. we have no problems with internal calls...
The problem occurs, as soon as the SIP trunk is involved (what is the case, if I call one of the extensions over the external number)...