has a switch under the battery slot labeled M/V.
What might this do?
Unique internal Music-Vocal switch allows choice of bass contouring for desired proximity effect best suited for specific instrument or vocal miking application
Sounds like a high pass filter switch to me.
One is for Music. One is for Voice. The latter having a low-frequency cut off/rolloff "high pass" filter. This compensates for the buildup of bass response from the Proximity Effect of working close to a directional microphone. Not everybody needs nor wants to use that switch. If somebody sounds particularly muddy on that microphone, engage the switch. If they sound too thin? Switch at the other way.
You shouldn't steal microphones without the directions to them.
Ms. Remy Ann David