+public:
+ Moment get_start_moment () const { return start_moment_; }
+ Real get_start_volume () const { return start_volume_; }
+ Real get_duration () const { return duration_; }
+ void set_end_moment (Moment);
+ void set_volume (Real start, Real target);
+ Real get_volume (Moment) const;
+ Audio_span_dynamic (Moment mom, Real volume);