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Distorted Audio

1170 Views 25 Replies Latest reply: Apr 22, 2011 4:56 PM by Blacknight582 RSS
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Barbara Smits Calculating status...
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Apr 20, 2011 4:43 PM

I have recently recorded a musical concert with a Canon XL1S video camera using 16 bit audio, two audio channels -- one channel for a line out from the main mixer and one channel for an ambient mic through a second mixer.  Both channels were set at line level input and both were recorded at attenuated levels due to large fluctuations in sound levels and volume from the musicians/group singers.  I heard no distortion through my headphones while taping and recording levels were set low enough not to distort.  Upon editing the sound in Final Cut Studio, I find that that both channels are suffering from some distortion, but the ambient mic run through the second mixer is suffering the most distortion.  For future reference, can you tell me why attenuated audio would distort in the editing process and not be heard during the recording process?  Thanks.

Small Town Gal

Mac Pro, Mac OS X (10.4.11)
  • NLEdit Level 4 Level 4 (1,645 points)
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    Apr 20, 2011 5:59 PM (in response to Barbara Smits)

    Barbara,

       Too many variables to give you a real answer. But normally there's no good reason the audio would be distorted by editing. If you were monitoring ahead of the camera head you wouldn't have heard anything happening at the camera input. If you monitored at the camera (wonder if it has confidence audio out) and it was ok, well, I'd go check the tape. If the tape straight out of the deck sounds fine, well, then there's a issue somewhere in your chain of connections getting the sound into your system.

  • NLEdit Level 4 Level 4 (1,645 points)
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    Apr 20, 2011 6:15 PM (in response to Barbara Smits)

    Sorry, no idea. Not the type of gear I use. I don't think I've touched one for years. But I bet someone here knows. My guess is that there is no difference. You have the one adjustment and something is lying to you. Did you monitor audio at the camera at the time of recording? If you did and it didn't sound distorted I'd guess that the audio port used wasn't putting out "confidence" audio, audio as it's actually going onto the tape, but instead as the audio comes up to the camera. Apparently too hot for the input. Aren't there meters somewhere on that deck or in the viewfinder?  Is all the audio distorted or just the peaks?

  • Studio X Level 7 Level 7 (26,835 points)
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    Apr 20, 2011 6:43 PM (in response to Barbara Smits)

    Setting to -4db with "nothing over 0db" is WAY too hot. The meters on the cam are not all that sophisticated and it is very probable there were transient peaks that hit the digital cut off without registering on the meters.

     

    fwiw - I record average levels around -12db and keep transients to -6db or so. This gives me adequate headroom for that unexpectedly LOUD section. That, and all the audio goes through a mixer with a limiter that will gently roll off the unanticipated spike before it gets to the cam.

     

    Did the audio engineer roll his own tape? If so, get a copy of it.

     

    x

  • NLEdit Level 4 Level 4 (1,645 points)
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    Apr 20, 2011 7:18 PM (in response to Barbara Smits)

    That's what I was trying to saw before AT&T refused to log me in. -12 is a good figure. We use -20 most of the time in the field. It's a pain for me in editing and mixing. But it assures my audio dog that nothing is peaking. Digital can handle the fain boost later. That assumes good gear that suppresses the noise floor.

  • Studio X Level 7 Level 7 (26,835 points)
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    Apr 20, 2011 8:49 PM (in response to Barbara Smits)

    All I can say is I do not trust any camera's audio section. This means turning off anything that smacks of AUTO.

     

    I want to feed it a signal of a known amplitude and not rely on it doing ANYTHING to process it.

     

    fwiw,  I will run a firewire audio feed from my mixer (Mackie 1220i) to my laptop to record just the audio (using Logic). This gives me the opportunity to record each microphone on its own track - often I'll have 3-5 in use. You have MUCH more control in post production this way. The camera audio is really only used for syncing the other tracks - so if it is funky - no real loss.

     

    Good luck,

     

    x

  • NLEdit Level 4 Level 4 (1,645 points)
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    Apr 20, 2011 9:34 PM (in response to Barbara Smits)

    let's back up a bit. Describe the "distortion." What are you hearing? Maybe you could post a piece of it.

  • NLEdit Level 4 Level 4 (1,645 points)
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    Apr 21, 2011 7:31 AM (in response to Barbara Smits)

    well this is why we'd like to hear the "distortion." the only real distortion in the digital recording world (and I generalize) is at peaking where you get anything from a pop to an explosion. The latter happened to us on the old Dyaxis back in '91. Scared the **** out of us.

  • thrillcat editorial Level 4 Level 4 (3,840 points)
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    Apr 21, 2011 7:35 AM (in response to Barbara Smits)

    There are two primary "line levels". A very blurry line is drawn between pro-equipment and consumer equipment, and that line is becoming fuzzier all the time.

     

    Basically, some gear's line level is -10db. Some is +4db. Sounds like you ran a +4db line level into a device expecting -10db. In this case, no matter what level you set it to record at, it's going to record distorted audio at that level.

  • NLEdit Level 4 Level 4 (1,645 points)
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    Apr 21, 2011 7:40 AM (in response to thrillcat editorial)

    Good point, but she monitored the audio and didn't hear any of the typical stuff you'd hear at that level. And even now, off the original tape, that sort of distortion isn't there. That's why I'd like to hear it.

  • thrillcat editorial Level 4 Level 4 (3,840 points)
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    Apr 21, 2011 7:43 AM (in response to NLEdit)

    Yeah, but without some serious in-ear monitors or airplane hangar cans, at a loud show, you don't hear what's coming out of the cans. Especially coming from a very weak headphone amp built into a camera. It's happened to me with pro Sony headphones. You think you're hearing what's coming off the camera, but really it's being overpowered by the room level.

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