The f_sound_id_ref is a reference to an earlier DefineSound tag.
The f_stop_playback can be set to 1 in which case the sound stops as soon as the next ShowFrame is reached. All the other flags should be set to 0 when this one is 1.
The f_no_multiple flag indicates whether the same sound effect can be played more than once at a time.
The f_in/out_point indicate the start and end points where the sound should start playing and where it will end. f_in_point should always be smaller than f_out_point. By default, f_in_point is taken as being 0 and f_out_point is set to the f_sound_samples_count value.
The f_loop_count defines the number of times the sound will be played back. I don't know yet whether there is a special value which means playback forever.