PBX Delivers Audio - poor quality

[Frazer]

Hi,
We have 50+ Yealink T46S configured with the following codec priority:
G722
PCMA
PCMU
G729

Trunk codec priority is:
PCMA
PCMU
G729

C:\Program Files\3CX Phone System\Bin\3CXPhoneSystem.ini currently set to:
LocalCodecs = G722 PCMA PCMU G729 GSM
ExternalCodecs = PCMA PCMU G729 GSM
3CX Media Service has been restarted since making the above changes, as well as the entire server.

All phones are local to the PBX, on the same subnet in a dedicated voice VLAN.

When making internal calls the audio is clearly lower when 'PBX Delivers Audio' is selected.
S's within speech are particularly poor quality.
Disabling this on both extensions increases the call quality.

The Yealink's both show up as a 'HD' call regardless of the above setting, suggesting both peer-to-peer and PBX methods are using G722.

Any ideas how to achieve peer-to-peer G722 quality while using PBX Delivers Audio or is this not possible?

Thanks

 

[nb]

Hi nb,
I understand the principals around transcoding, going from high-low and low-high.

I was not expecting G.722 to be used during external calls. I would expect the external calls to be of lower quality as they are using PCMA with a different bitrate/sample rate/codec so transcoding is necessary from G.722 to PCMA, as per configuration in the trunks.

The problem is G.722 on internal calls (where bandwidth is not an issue) AND when 'PBX Delivers Audio' is ticked, or when 'Record All Calls' is ticked. The resources available to our 3CX server are quite high and it is up to the customer to decide what resources they can provide to the server.
Both phones support G.722 as does 3CX - no need to transcode or down-sample the G.722 codec.

When making an internal call I wouldn't expect any transcoding to be done at all, just pass-thru at the same codec/bit-rate/sample-rate while recording the audio.

Are you saying _by design_ 3CX will down-sample internal calls when 'PBX Delivers Audio' and 'Record all calls' are ticked regardless of the codec priority?

1) No its up to you to tell the customer what resources he needs to apply. If this is my customer and he has X amount of calls, I will go and tell him "You need this machine - and these resources because I am the expert and you are not. If you dont do this, go ahead but don't call me". This is a pbx not some notepad application. and if it is busy, then come on...

2) To elaborate for you..
So 3CX, once the option PBX Delivers audio is enabled, it will Transcode. Transcoding is not subject to whether it is a local or external call. Its simple - if the option is enabled, it will transcode all calls. EVEN IF IT IS NOT NEEDED!!! (Yes it sounds funny but it is how it is). And there is a reason for it.

There are features like SRTP, Barge in and recording. these features force media server to Transcode and MIX FORCEFULLY. So when you have a G722 stream and another device also sending a G722 Stream, if the pbx delivers audio is enabled, TRANSCODING WILL STILL OCCUR (even though it is not needed technically). Because if we don't do this and some guy tries to barge in on a call, there will be no audio..

For now I suggest that you remove remove all PBX Delivers audio and set all phones to G722 and PCMU/A as second. Get the provider and leave PCMU / A.

On a side note, We do have plans to improve this possibly in V16. There is legacy code coming from the old days that says Transcode if option is on. This is because transcoding also solves Media issues related to NAT. But now routers and firewalls are doing better jobs delivering media so transcoding is no longer required to solve one way audio issues. We will definitely improve this..

 

[Frazer]

I removed 'PBX delivers audio' a while back in this thread - I think this was left on by our initial setup (not sure why, I didn't do the initial setup, but this thread has helped me to realise it should not be on), that has solved the problem of 'PBX Delivers Audio' lowering the internal call quality.

When we did further testing, we discovered 'Record All Calls' had the same issue. We do want to implement 'Record All Calls' on some extensions so we have proof of abusive callers.

Our setup from the start was G.722 1st and PCMA 2nd in the codec order on phones for internal calls, PCMA is 1st for the trunk codec.

1) I am the customer, I over-provisioned our 3CX resources to avoid any issues with quality because our Hyper-V hosts have more than enough resources available. Once we discovered the issue, I posted here.

2) Thanks for explaining the process, lets hope V16 goes some way to restoring the call quality when recording.

 

[nb]

Hi guys

Good news and as promised... we do have an update on this.

We have a build that will upgrade the frequency of the media server mixer to 16 kHz when required, specifically for those cases when one of the participants has a G722 negotiation.

Anyone who wants to try this, please send me PM so I can provide instructions. This fix will be included in the upcoming v15 SP5. Please specify if you want windows or linux build.