such as the sm57? got a friend coming in who insists on using the sm57 for recording his voice and i've never recorded vocals with it before. should i let him sing right on top of the mic with his lips touching the grill like he does at live shows? or should i try to get him to back off 6 inches or so like with condensers ? should i use a pop screen? any tips or general rules for recording vocals with this microphone?