So, I've had my HD7 for a few months now, and I'm quite pleased. Recently I've decided to invest in an external mic. I already have a boom pole, shock mount and some cables, so all I needed was the mic. I went on ebay, and stupidly, without much research, I bought the Audio-Technica ATR-55.
http://www.audio-technica.com/cms/wired_mics/8db33c5971d3add5/index.html

I plug it in to my camera, it works okay, but I realize that it only records on the left. When I play the footage back in my NLE with headphones on, and I only hear it in my left ear.

So, I'm asking, since I'm confused, can my mic work? Do I need some sort of stereo mic? Any help would be very appreciated.

Most if not all NLEs have a 'Fill Left' preset that would take and duplicate the left channel onto the right channel. This is what you'll need.

I shoot pro video using a similar Azden mic, the reason it records to only one channel is that it is in fact a mono mic. There is no reason during capture to duplicate it to both channels, though there might be an option, as there is on the Z1 (what I use). The mic is fine, you just need to customize your workflow to properly deal with it. A good example would be that many shoots I've done has involved 1 lav mic and 1 boom mic, recording separately to L/R. In post production, I mix the two together, and make sure the levels are balanced. That way, if one is too loud over the other, I can fix it. If it mixed them, I would not be able to.

C

Thank you so much. I found an option to combine the L/R tracks that I didn't even know to look for.

I have a mono Sennheiser MKE 300 that did record to only one track, and used a mono to stereo adapter on the jack. I get sound on both channels, and with the earphones plugged in the VA jack with Steve's adapter, I am also able to monitor the sound live.