Thanks for interesting info again. I have just moved from Ukraina to the republic of Moldova, so it's not so easy to test things out, here either, but its still interesting to work on "the theory".
I think that the following can be summed up:
1. Signal prossessing and data transport for Asterisk is a realtime application.
2. It has been recognized for a while that a standard Linux kernel do not perform "true realtime prosessing".
3. In environments that is working with or using ip telephony it has been quite usual to concider that IP telephony gives slightly porer sound quality than ordinary analogue telephony.
The interesting question is then: When the real time signal processing is performed by the same kernel that also handle quite other processeses like web servers, dastabase servers, etc, will this reduce the capabilyty to perform true realtime processing for the IP telephony function ?
I think that in some way it is likely to believe that the answer is "yes" and that the properties of the kernel, how the Asterisk program is processed by the kernel and the amount of load on the kernel by other processes will have influence on the real time capability, and therebay also the audio sound quality.
If this should be true, one basic design rule for well functioning Asterisk servers (and other iptelephony servers) should be: Let the ip telephony server allways have its own dedicated processor, and never try to mix it with general server processes and general processing platforms like the SME server.
It would be very interesting if also someone testet out for instance Astlinux as the dedicated Asterisk server versus Asterisk on sme or Centos as a more general distro, to come up with a conclusion - yes, there is actually a difference in sound quality, or the oposit - no, there is no hearable difference at all.
Actually I do not trust myself, to much but, I believe that there is a hearable difference that can be confirmed.
From this interesting discussion I will say the well known words - I'm still confused (and I have a bit daubt about it all), but on a higher level.
Anybody else that has tested and compared sound quality ?