Someone I talk to on Skype a lot has a very persistent issue, where after a few minutes their voice goes very 'robotic'... still understandable but annoying. We can restart the call and it's fine, but fairly consistently after a few minutes it returns.

He experiences this with other people too, not just me - I don't have anyone report problems with my audio quality.

This is not an ISP issue - he gets the same problem on multiple PCs in different countries, in fact he's even recently moved to a different continent and got a new internet connection... same problem.

It seems somehow to be a problem with his Skype account, which is really quite odd. It's been going on for months of not longer.