Import Cover - Filename 'conversion'

I have exported 1005 covers with the export parameters %artist% - %title% and converted the png to jpg. Than I deleted all the covers out of the mp3 and began to import. But the import only imported 878 covers.

The problem is that I need a kind of conversion from the artist title name to the allowed filename characters.

The titles with a "?" had created a filename without that "?" (Eurythmics - Why? => Euryhmics - why.jpg)
If I do the import the system tries to find a eurythmics - why?.jpg which doesn't exist.

How can I convert the %artist% - %title% parameter to the allowed (filename) characters. There must be a rule because for the export there's an automatic way.

Thx

Did you try $validate(%artist% - %title%,)?

No, but I will try it soon and post, how it works.
THANKS

OK, $validate(%artist% - %title%,) => that works as expected
but you have to do it on both sides for Export & Import