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I'm shooting footage on a college campus using a wired external shotgun. In certain places on campus, there's an occasional buzz--like someone using a sped-up morse code--followed by a few seconds of thumping. It doesn't happen all over campus, and it's not constant. Since the environment is a college campus, there's a ton of stuff "in the air": phones, internet, the campus network, security guards on radios... First, could these be the causes of the interference, and if so, is there something to do about it?

Thanks for any advice.

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FYI, interference sounding a bit like morse code could be GSM cell phones — the radio protocol was defined such that it has audio-frequency components. –  Kevin Reid Oct 7 '11 at 12:33
    
What kind of shotgun microphone is it? –  leftaroundabout Oct 7 '11 at 21:14
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1 Answer

Those sorts of things could definitely be causes - but you probably can't do much about telling them to stop, so you should concentrate on what you can improve:

The wire between the mic and the camera is going to be the biggest problem - it is acting as an antenna, and as microphone signals are very low you need to improve your signal to noise ratio.

Options:

  • Use a shielded or balanced cable - probably your easiest option. You can get balanced cables for mics that are very resistant to interference but this will depend on what your camera supports
  • Use a pre-amp at the mic to increase the signal - this reduces the effect interference will have
  • Record audio at the mic (thus shortening the wire) and add it to the video later - you will need to look at synchronisation, etc
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