clipping a camera when the meter say it's not

Discussion in 'Amateur Video Production' started by Ty Ford, Sep 16, 2012.

  1. Ty Ford

    Ty Ford Guest

    HI,

    I ran into a familiar problem last night on a shoot but decided to try a
    different solution.

    After calibrating my mixer to the camera, line to line, we tested and found
    that unclipped audio from the mixer was clipping the camera even though the
    camera's meters were not close to clipping.

    I have run into this before and switched to feed the camera mic to mic level,
    which worked, but there you are at mic level.

    This time we tried something different. Camera stayed at line level input. I
    switched my Sound Devices 442 to -10 output and re-calibrated. Much better!
    No clipping.

    I have talked with others about cameras with "soft audio front ends" that
    clip too early. I'm thinking the mfgr chose the wrong standard (if any) to
    design the audio front end. Sort of like the Red when it first come out.

    So if you run into this, there may be another solution than to drop to mic
    level.

    Regards,

    Ty Ford

    Try my new blog; http://tyfordaudiovideo.blogspot.com/
    Try my audio sample archive: http://tinyurl.com/796z25d
    Try my gear reviews: http://tinyurl.com/79q797r
     
    Ty Ford, Sep 16, 2012
    #1
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  2. Ty Ford

    Don Pearce Guest

    I've come across this before. It was caused by the camera having a
    pre-amp before the gain control. The pre-amp clipped, but the gain
    control stopped the signal peaking the meter.

    the solution was to make sure that (in this case) the camera gain
    control was always above 7, and turn down the input level to suit.

    d
     
    Don Pearce, Sep 16, 2012
    #2
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  3. Ty Ford

    Scott Dorsey Guest

    Yes, I carry around a few of the Shure adjustable pads for just this
    application.
    This is a matter of headroom. The thing is "+4 level" in that you can
    feed it a reference tone at +4 and it won't clip. But, once you put a
    real world signal in that has a lot of peaks well above the reference
    level, it clips. Part of this is a matter of people using average-reading
    meters for levels of equipment that clips due to peak levels.

    This is what the headphone output is for!

    Note that some of those cameras have the same front end for line and mike
    anyway... when you switch to line level they insert a pad....
    --scott
     
    Scott Dorsey, Sep 16, 2012
    #3
  4. Ty Ford

    Trevor Guest

    You've just got to be aware that anything that is not designed for +20dbu
    peaks, and uses a digital input attenuator, is going to clip regardless of
    it's own settings. When you can't switch the mixer output to consumer level
    as you have done, you can simply insert a real pad before the camera input.
    I never leave home without one, and a box of adapters :)

    Trevor.
     
    Trevor, Sep 17, 2012
    #4
  5. Ty Ford

    billy Guest

    Yes, the crest factor of a sine wave is a lot lower.
    I made up a bunch of cables of various lengths, with 1/8" stereo phone
    plugs on one end and 1/4" (cable-mount) jacks on the other. Some cameras
    have speakers in them, and unplugging the headphones sends audio to the
    speaker, unless you turn down the volume pot - which is sometimes a pain.
    So, I connect my cables, which keep the speakers muted, and then someone
    competent can frequently check the audio easily, and quickly. I have
    this done (roll back and listen to playback) at least after each scene...

    Billy Y..
     
    billy, Sep 17, 2012
    #5
  6. Ty Ford

    John Hardy Guest

    A customer of mine had a similar problem many years ago when sending the
    output of an M-1 mic preamp to the input of a Wadia A/D converter. It
    turned out that the Wadia unit had an input stage that was operating
    from +/-5VDC supplies ("five volt" supplies). So, any input level above
    +8dBu or so would be clipped by the input stage of the Wadia. Then came
    a level control, followed by a meter. So, the input stage would clip,
    the level control would turn the level down to a point where the meter
    would tell you that all is well.

    Dumb design.

    By the way, the meter of the M-1 indicates the level of the output of
    the M-1, and there is no way to have distortion earlier in the signal
    path before the output clips.

    Thank you.

    John Hardy
    The John Hardy Co.
    www.johnhardyco.com
     
    John Hardy, Sep 18, 2012
    #6
  7. Ty Ford

    Ty Ford Guest

    Thanks for that, John.

    The camera, BTW, was a DMC 150 Panny.

    Regards,

    Ty Ford

    Try my new blog; http://tyfordaudiovideo.blogspot.com/
    Try my audio sample archive: http://tinyurl.com/796z25d
    Try my gear reviews: http://tinyurl.com/79q797r
     
    Ty Ford, Sep 18, 2012
    #7
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