What would you do if you heard a woman being beaten up by her bf or husband?

I'm just wondering what you would do if you heard the wails and screams of a defenseless woman coming from an apartment or house and the unmistakable sound of his fists and hands inflicting such pain? Would you think it was none of your business or that you don't know the full story? Would you call the cops? Or would you intervene by knocking on the door yourself? In your response please state if you're a male or female. Thanks.