rncbc.org a.k.a. Rui Nuno Capela

So it's a freeze, not a crash.

Are you sure you aren't missing an ampersand (&) at the end of the alsa_in or alsa_out command lines ?

You need that for any of those commands to run in the background, otherwise QjackCtl just gets stuck indefinitely while waiting for the scripts to terminate. And it might just look that it freezes, because neither alsa_in nor alsa_out does immediately exit() if started successfully ;)

Check that out.