[Asterisk-Users] choppy and cracking sound from zyxel prestige 2002

[listasterisk.20.eenewz at spamgourmet.com]

Steven Critchfield - critch at basesys.com wrote:
>>
>>Does anyone have suggestions hooking Zyxel Prestige 2002 to Asterisk?
>>
>>I have tested Zyxel Prestige with both supported codecs.
>>
>>Call with G.711 sounds very choppy and cracking. Almost can't understand 
>>a word.
>>
>>Today I installed G.729 support into Asterisk but unbearable voice 
>>quality remains. It's a little bit better though.
>>
>>I have tested that Zyxel ATA with some commercial SIP providers 
>>(stanaphone, simpletelecom etc.) and the quality is OK.
>>tcpdumping connection with both providers showed that G.711 alaw/ulaw 
>>was in use.
>>
>>Some Grandstream phones are also hooked into that same Asterisk pbx and 
>>using G.711. Those devices voice quality is superb.
>>
>>Firmware installed in Zyxel Prestige 2002 is V3.60(MD.2)C0 (latest).
> 
> 
> Have you tried the (seemingly) standard problems/fixes. Make sure VAD is
> turned off. Quick test might be to make noise on your end and see if
> quality increases. Possibly play background music loud enough to
> transfer to the far end. If so, track down how to turn VAD off.

Yes, but no luck :(

When VAD was turned on sound quality was even worse.

Calling with G.711 to voicemail sounds very robotic and cracking.
Sometimes playing music on hold mp3 loop via G.711 gets a little bit 
better for some seconds. But then cracking and distortion starts again.