Ah-ha, running jack-dssi-host fluidsynth-dssi.so creates the same white-noise sound, so it is not Rosegarden, it is something wrong with fluidsynth-dssi (but not fluidsynth standalone)
Ah-ha, running jack-dssi-host fluidsynth-dssi.so creates the same white-noise sound, so it is not Rosegarden, it is something wrong with fluidsynth-dssi (but not fluidsynth standalone)