Codec G722 vs G711

[Marcel Junk]

Hi,

we Running latest 3cx Version. - We use as Client the 3CX Client and Yealink T41X T42X Phone.
Our Provider Support G722 aka HD Voice... to i think to switch to G722

At this moment we use G711u, G711a , G722 as Codec for Internal and External Calls.


The Yealink Support HD Voice so i switch for a Test some Phones Codec Order: G722, G711u , G711a on the Phone in Display is shows: "HD Voice" - But the Sound is horrible....... it sound like a old phone... very bad qualy.

the same on the 3CX Soft Client..... i tryed with "PBX Deliver Audio and Without".

Is this normal ? - Or is there a "settings" that i forgot?

PS: the Clients are connect via LAN in our Office.

Best Regards,
Marcel

 

[cobaltit]

So does the quality sound bad on internal calls (extension to extension) or just external calls. If only external calls I'm assuming there is some transcoding going on that is degrading the sound. It's great that your provider supports G.722 but you'll want to look in the logs or wireshark to confirm it's actually being used.

 

[Marcel Junk]

Hi,

its Internal / External the Same.

On g711 good on g722 bad

 

[Marcel Junk]

okay, Upgrade...

i ch3xk my configs... there was a Problem with the Internal Phones.

We have some phones in Branch Office, ther are connected via Stun direct. with this phones are the Problem.

Internal in my lan evrytging is fine.

Best Reagrds, Marcel

 

[YiannisH_3CX]

Hello @Marcel Junk

First you need to make sure that you have enough bandwidth to support calls with G722 as it much more demanding than G711. Then you need to make sure that all the audio streams are G722 so there is no transcoding taking place which might affect quality.
Set G722 as the primary codec under your extensions and try a call between them first. if that is ok then try a call from the provider. As a test you might want to remove all codecs from your trunk settings except G722 and test

 

[nobody]

I also tried G722 (yealink T4/T5, Android, windows phone). Same results. It sounds "metallic", or, "hissing", or sounds like transcoding a sound file with a buggy vlc version. However, a customer of mine using starface and yealink has no such problems.
It also does not change if I switch between qsc or dus.net (both supported providers)
I tried to make sure that none of the low bandwidth G722 codes are used only the high quality. The T46s displays a "H" and the T58 a similar symbol during the call.
Switching back to G711 will fix the quality problems immediately.
I don't need G722, but I think if it is used the quality should be about the same as G711.
Since the other party using yealink (T48G not S) has no problems, it is unlikely that the phones itself are the culprit.
How can I find out if the 3cx phone system is transcoding the call or not? I have set the record all calls feature to on.
3cx Version is: 15.5.15502.6

 

[YiannisH_3CX]

@nobody

You will need to use wireshark to see what codec is negotiated between the provider and the PBX and make sure that no transcoding is taking place. You will also need to see the codec negotiated between the phone and the PBX.

 

[nobody]

ok, Wireshark shows that the desk phone (T58V) speaks G722 to the pbx. The PBX speaks G711 to QSC. So, transcoding is done in the PBX.
Still, I don't see a reason for the IMO bad quality. That could be done better.

 

[YiannisH_3CX]

Transcoding means that the PBX will try to change the format and quality of an audio file to match the codec of the other call leg. During this process some quality may be lost as the PBX will try to upscale or downscale the audio. In lack of a better example think of an non HD image displayed full screen on a full HD display that does up-scaling. The CPU will try to fill in the blanks but it won't do a perfect job. For the best audio quality make sure that you are using one codec across the board so no transcoding is required.

 

[nobody]

Yannish,
Thank you for you reply. But still I think there is a problem in the used decoder/encoder. G722 is a wideband codec, and G711 carries less information compared to G722:
G711: 8Khz, 300-3.4khz
G722: 16khz, 50-7khz

Transcoding from G722 to G711 should be possible without loss of quality compared to using G711 in the first place. Its like reducing the size of a jpeg which normally can be done without quality loss. I partly agree with you the other way around, if you transcode G711 to G722 - which will happen with the data the called party sends, then you have to interpolate data. But regarding the frequency range this should not be a real problem because you can limit the frequency range to what G711 allows, and apply a digital filter with noise or silence. I guess a current version of ffmpeg will deliver perfect quality. I will make a test if I have the time. Then we know that for sure.
Also, the pbx from starface seems to have no such problems. So, it is doable..

Another thing is how to use G722 without transcoding? The provider I use (QSC) supports G722. Now, to use G722 I have to put it on top of the list of preferred codecs. There are 3 places where this can be done:
PBX settings
Trunk settings
Phone settings

I think, if I want to use G722 the preference should look like this:
G722
alaw
ulaw

But if I do this, and make an outgoing call, QSC will most of the time force G711, so the pbx has to transcode. Only calls to customers which also use QSC will be done using G722.
If I dont put G722 on top of the list it never will be used if I start the call. Or is there a setting which will renegotiate the used codec from the pbx to the phone if the provider enforces G711?

 

[YiannisH_3CX]

If you provider supports G722 in all call scenarios then you could only have G722 under your trunk settings removing the other codecs. This will force the provider to negotiate G722 for every call. But if QSC does not support G722 for certain call types like international calls then calls will fail.

 

[Lee Cramman]

Note - if you're playing with CODEC priority in phone provisioning or hot desking you may need to re-provision the endpoint after each change before it will take effect.