> I assumed that hardware / software does
> automaticly set the speed to a reasonable value.
And you assumed correctly. If media is *properly* supported by firmware
you have *all* rights to expect that firmware automatically picks
reasonable speed for it.
> And now after playing around a long time I figured out
> that the media is designed for 1x ;-)
And formally you have all rights to expect that you firmware recognizes
it as 1x media. As growisofs manual page implies -speed=1 is everything
> Nevertheless, I tried the version 5.13 as you recommended
> but I can't switch to speed=1 (error message, that growisofs
> can not switch to this speed).
> When I use 5.14 and speed=1 it burns with 2x.
Failure to set or pick expected speed means poor media support by
firmware [or simply broken firmware].
> What can I do?
Test several media brands and stick to one which works with your unit.