my local copy defaults to both, and the helpfile shows this
-0 Synthesize no audio
-1 Synthesize audio for the first DMR timeslot
-t Synthesize audio for the first DMR timeslot
which would obliquely imply that -3
should be the unlisted default to synthesize all DMR audio (which is evident in the menu toolbar), yet it is an invalid parameter.
The nuances in DSDPlus documentation, help file and GUI are always interesting.