[Asterisk-Users] Distortion/crackling/skipping problems on outgoing calls -- please help!!!

[Robert Geller]

Rich Adamson wrote:

>>So, can no one give me any suggestions? Perhaps I can elaborate upon 
>>further testing and attempts to debug this tremendously frustrating problem.
>>
>>My softphone (typically IAXComm, but same results connecting via SIP on 
>>Xten Xlite)  is installed on a P4 1.6 w/ 256 megs of RAM and an 
>>integrated sound chipset (Intel/AC97). I've had some problems with this 
>>chipset in Linux, and it doesn't support hardware mixing, so I've had to 
>>attempt to get dmix and ALSA running in an acceptable fashion; needless 
>>to say, I still have problems, and I don't know if this is related.
>>
>>I can record and playback my own voice and other audio (podcasts, Net 
>>radio, and music) fine with this headset (some cheap, Chinese $15 
>>headset). However, when it comes to receiving decoded audio on the other 
>>end of a VoIP conversation, it sounds "scratchy," distorted, crackly, 
>>whatever you want to call it. It's not the clarity so much as it is the 
>>other things I just mentioned. It's very hard ot put into words, but I'm 
>>hoping *someone* can associate with my problem.
>>
>>To make sure it wasn't my Asterisk box that was mucking things up, I 
>>connected directly with my softphone to my outgoing VoIP terminators, 
>>voipjet and Voxee. Sure enough, it sounded *exactly* the same as it does 
>>going through my * box on the LAN and then out through the public Net to 
>>voipjet and/or Voxee. Thus, I know it is my side of the equation that is 
>>mucking things up, but I cannot for the life of me pinpoint exactly 
>>*WHERE* this is taking place.
>>
>>Actually, I also unplugged my headphones and plugged back in the 
>>speakers, and it sounded roughly the same, but it's harder to tell 
>>because they're not surrounding your ears, quality isn't as clear, and 
>>ambient noise can be more easily heard and is distracting.
>>
>>I'm thinking, at this point, that it's my sound card that's messing 
>>things up, or its configuration or something. However, can anyone 
>>explain *why* non-VoIP-conversations sound perfect on my speakers and 
>>headset, while VoIP calls sound very bad?
>>    
>>
>
>If I were to try to diagnose the above, I'd be using Ethereal to 
>capture the voip packets coming from your itsp's, and analyzing 
>that captured data to look for unusual things.
>
>If your itsp connections are sip based, ethereal has a utility to 
>analyze/summarize some of this for you. If those connections are iax
>based, then you will need to analyze the packets yourself looking
>for unusual things.
>
>Analyzing the packets (either sip or iax) can consume a lot of time,
>but you really need to ensure those packets are arriving in a consistent
>manner, timestamps contained within the packets are consecutive and
>proper, packets are not arriving out of order, etc. At the same time
>that you're capturing those packets, use the facilities within asterisk
>to summarize what it thinks is going on (eg, 'iax2 show netstats'),
>so _that_ data can be correlated to the info derived from the packet
>captures.
>
>If this is a small soho * system, then run ethereal right on the same
>asterisk system capturing the data as it arrives at the system. Doing
>so will help identify any issues that you might have involving your
>local lan, broadband issues, etc, etc.
>
>Assuming the problem that you've described is consistent and happens
>on a regular basis, you don't need to collect and analyze megabytes 
>of packet captures. Just collect a short duration sample that is 
>assured to contain the representative packets associated with the
>bad audio (maybe five or ten seconds worth). If the analysis does
>not indicate a problem at that point, then at least you know the
>problem is internal to asterisk, etc.
>
>If you don't feel you have the skills or knowledge to do that
>analysis, then hire someone that can.
>
>Both your original post and the followup post contain a ton of 
>adjectives and adverbs describing a technical problem, but contain 
>little (or no) technical data (such as the results from above or 
>results from various * show commands) that would allow anyone to 
>comment on your problem. So, doubtful anyone is ever going to reply
>to such postings with anything helpful.
>
>  
>
Thank you very much for your response. I do acknowledge that my previous 
posts did not contain much technical information to speak of, but it was 
mainly because I wasn't/am not familiar with the Asterisk CLI and 
troubleshooting Asterisk problems, so I apologize for that.

I did get the idea early this morning to try to analyze packets with 
ethereal, and I captured packets when I was made an internal IAX call to 
the Asterisk system (voicemail). I don't really know what to look for, 
but I will learn (again, I'm not very familiar with ethereal). Do you 
hapeople say ve any suggestions for filters to use, to evaluate possible 
packet loss or resending of data?

Regarding the command that you suggested in the CLI, iax2 show netstats, 
it doesn't recognize that command or anything similar, and 'help' 
doesn't return anything similar that I can see (I'm using 1.0.7 if that 
helps).

At this point, I'm thinking that it could be a matter of bad cabling or 
something. The Cat5 cable that's running the 8 or so feet from my PC to 
my router is homemade by me, and many people do report problems with 
homemade cables. I may not have made it exactly right, or the untwisted 
segment may be longer than 1/2", which supposedly causes distortion and 
interference. Perhaps I ought to run out and buy a couple factory-made 
cables to test the difference, if any, between them.

Regards,
Robert Geller