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Mics in noisy areas, recording a distant but significant signal

Discussion in 'Microphones (live or studio)' started by janos.papp, May 2, 2017.

  1. janos.papp

    janos.papp Active Member

    Joined:
    May 2, 2017
    Location:
    Hungary
    Hello!

    I have a use case, where I need microphones in traffic situation, attached them to a car. The estimated noise in this situation is around 56dB. In our use case, we shall detect ambulance/police/fire truck sirens from a distance, where usually people ears can listen as well. What kind of microphone/microphone setup do you recommend for this use case?
    After some research, I'm thinking about:
    - omnidirectional MEMS microphones - gets sounds from all around, even from the back of the mic, so the ego-noise shall be cancelled
    - 2-3 cardioid mics - the ego-noise is canceled because of the architecture.
    Other than that, what parameters shall I check when I choose microphones?

    Thanks for your further answer!
     
  2. Boswell

    Boswell Moderator Distinguished Member

    Joined:
    Apr 19, 2006
    Location:
    UK
    Home Page:
    The last time I was involved with this sort of thing was for a budget film (video) that needed surround sound. The action for this particular scene was shot on a disused airfield, and involved a vehicle being buzzed by a helicopter. The vision shoot was done first, then they wanted the Foley sound pass. I taped four omni boundary microphones spaced out on the roof of my car which I fed into preamps and an Alesis HD24 recorder powered via an inverter. I set the recorder running, then drove along the runway while the helicopter came worryingly close overhead. It worked out surprisingly well. The sound editors did a great job in blending it with the action, and the surround sound for the helicopter was very realistic, including plenty of 20-30Hz blade turbulence. However, I was alarmed to hear all the gunfire in the final cut, which I somehow had missed during the recording.
     
  3. janos.papp

    janos.papp Active Member

    Joined:
    May 2, 2017
    Location:
    Hungary
    So in this case you wanted to record a scene, where some action happened, also gunfire had to be recorded by your set up, and the helicopter was used for filming and was a disturbing factor?
    If you say it was worked out surprisingly well... in case the helicopter was really close, you were able to record significant signals like gunshots as well? Maybe in this disturbed states, 4-5dB SNR is sufficient... what do you think?
     
  4. Boswell

    Boswell Moderator Distinguished Member

    Joined:
    Apr 19, 2006
    Location:
    UK
    Home Page:
    Not quite - I was using a slightly dramatic turn of phrase. What I had to record was the close-up noise of a helicopter flying low over a moving car. The gunfire was added from a separate source by the sound editors during mixdown.

    The reason I got involved was that the producers had tried canned sound effects of a helicopter flying over a fixed array of microphones, and it didn't give the result they wanted. Apparently the surround sound spatial perception of a fast-moving helicopter is different from a static or slow-moving one. Since they had to shoot the video sequences on the airfield, they came up with the idea of doing sound recordings at a few different moving speeds while the helicopter was still available. I don't know which speed pass was used in the final cut, but I remember having to drive at over 100 mph for the last run.
     
    pcrecord likes this.

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