>I badly need an english term for the following
>(in German: Tonfrequenz-Rundsteuerung,
>in Hungarian: hangfrekvencias ktrvezirlis):

This is what is sometimes called tone control, which I think you will find
is a reasonably literal translation of the German.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.