A woman plays bass and sings with her bandmate with is a man playing guitar and the drummer plays in the background.
The people are playing for a crowd
A woman who sings with a man playing guitar and a drummer are not necessarily playing for a crowd.
(x)
exists e1 x1 x2.(n_people(x1) & for(e1,x2) & n_crowd(x2) & Actor(e1,x1) & v_play(e1))