Music quality differencewith G711a codec between a fixed or Call call.

[support_alkivi]

Hello,

We have conducted several tests with different styles of music, and always get the same result:

• When a caller calls from a landline, our hold music is of good quality.
• When a caller calls from a GSM line, our hold music has a slightly distorted effect, with a kind of light white noise in waves.

In both cases, the same codec is used, G711a (analysed by tcpdump to be sure).

We have tried several things: Reducing the volume of the wav file (via Audacity) by removing a few dB, etc. Testing different export approaches (exporting at 8000 Hz) at the end of the project or working from the beginning at 8000 Hz. Testing music with more or less treble or bass. Always the same result.

What could explain such degradation with a GSM call?

Thank you in advance,

 

[AWS2P]

Are you sure about codec used while in GSM call ?

 

[support_alkivi]

As written :

"analysed by tcpdump to be sure"

I'm 100% sure

 

[ivank]

>> What could explain such degradation with a GSM call?
Transcoding somewhere down the line to the codec used in the mobile network.
Even if the audio from PBX reaches the cellular network provider intact, most likely it will be transcoded into something "less fat" than G.711 for transmission from BTS to the cell phone.

 

[jade1]

Try to check the Transcoding and the DTMF relay parameters

 

[support_alkivi]

Thank you for this answer, it seems the most logical explanation indeed.

>> What could explain such degradation with a GSM call?
Transcoding somewhere down the line to the codec used in the mobile network.
Even if the audio from PBX reaches the cellular network provider intact, most likely it will be transcoded into something "less fat" than G.711 for transmission from BTS to the cell phone.