Prolonged music on hold via line-in produces audio clipping

I have successfully configured Trixbox (Asterisk 1.4.22-3) such that people can call in to listen to a public lecture. They dial an extension, and then they are placed in the music on hold queue, which is actually playing audio that from the computer’s line-in port.

Everything works. The problem is that for people that have dialed-in, the music-on-hold audio quality begins to suffer, exhibiting a consistent “clipping” or choppiness, or stuttering. The Trixbox’s canned welcome message played to new callers is fine – no audio problems at all. But the MOH is clipping, and I can’t figure out what is causing it.

If I reboot the Trixbox, the problem goes away for a little while (no clipping). But after 10-60 minutes, it returns. I’m a total Asterisk/Trixbox noob, but it seems like potentially a buffering or interrupt issue. I’ve tried different codec settings to no avail.

Anyone have any ideas?


At a guess, you have a discrepancy between the sound card clock and the nominal Asterisk clock.

I would investigate using the Asterisk console channel drivers. I don’t know if you can auto-answer them, but you should be able to add jitter buffering. You could also try subscribing the console channel to a conference.

Also don’t exclude the possibility of using a phone to provide the audio capture.


Are you using meetme conferencing ?

if so this does require timing and can/does give variable quality if no hardware or usb clocksource is used