You may need a powered microphone. Many of the mics that I’ve used on consumer and prosumer cameras that only have a 1/8-inch mic input came with a button-type battery that would power the mic. Without that, the mic does not have the power to send the signal to the camera. Here’s an example of what you may need. http://www.soundprofessionals.com/cgi-bin/gold/item/ATR3350iS
