[asterisk-users] scratchy sound

[Vieri]

Hi,

I'm experiencing a few (but meaningful) cases of audio distortion (or bad quality). I can't say yet how often this happens.

Please listen to the following sound file:

http://213.96.91.201/temp/distorted_audio_1.wav

This was recorded by Asterisk while the local SIP caller was dialing out a SIP trunk (so the problem is on my side, definitely, and it doesn't seem to be related to the bandwidth between my peer and the SIP provider). You can hear a scratchy sound during the whole fragment.

I can't determine the possible cause of this kind of distortion. Maybe an expert ear can give me a clue. It shouldn't be the Asterisk server's CPU usage. Could it be a network issue between the Asterisk system and the SIP client? (it happens with SIP hardphones as well as softphones so I guess it's improbable it's the client software/firmware) Both softphones and hardphones use GSM and usually work fine (this kind of issue is not too frequent). The LAN isn't dedicated to voice but has QoS prioritizing VoIP.

Could the cause of the distortion be network-related? And only on "my" side? Should I consider other causes?

Thanks,

Vieri