1 2 Previous Next 25 Replies Latest reply: Apr 22, 2011 4:56 PM by Blacknight582
Barbara Smits Level 2 Level 2 (220 points)

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)
  • 1. Re: Distorted Audio
    NLEdit Level 4 Level 4 (1,645 points)

    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.

  • 2. Re: Distorted Audio
    Barbara Smits Level 2 Level 2 (220 points)

    Dear NLEdit:

     

    I just played the tape in the camera and listened to the audio through the headphones -- channel two is also distorted in the camera.  Do you know if the Canon XL1S somehow changes levels on the second channel? There is only one audio level adjuster and a L/R balance adjuster on my camera, so I cannot adjust the second channel separately -- although I really can't adjust anyway while using attenuated audio.  Any other thoughts out there?

    Barb

  • 3. Re: Distorted Audio
    NLEdit Level 4 Level 4 (1,645 points)

    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?

  • 4. Re: Distorted Audio
    Barbara Smits Level 2 Level 2 (220 points)

    I did monitor at the camera while I was recording and the levels did not peak over 0db -- attenuated sets it at about -4db, I believe, and that is what was showing on the level meters, each channel doing its own levels.  A "Pro" was manning the mixer sending me the master line level, and I was monitoring my mixer for the ambient mic -- should have been what I was hearing through the headphones -- always worked before.  The only difference this time was that I used the ambient mic through a mixer because you cannot set a mic level and a line level in the XL1S -- you can only set one level for both channels, so I chose a line level and ran my ambient mic through a mixer to get the line levels to be the same.  The only audio that seems to be distorted (I haven't gone through the whole 2-1/2 hours yet!) is when the entire group sings.  I think what is happening is that the group signal is way too hot compared to the individual singers, but shouldn't the attenuated setting adjust for their levels? 

  • 5. Re: Distorted Audio
    Studio X Level 7 Level 7 (26,940 points)

    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

  • 6. Re: Distorted Audio
    NLEdit Level 4 Level 4 (1,645 points)

    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.

  • 7. Re: Distorted Audio
    Barbara Smits Level 2 Level 2 (220 points)

    Dear All,

    When I am not using attenuated level settings, I normally do keep my levels around -12db if I am adjusting manually, especially in a situation like this when levels fluctuate so dramatically.  I don't remember for certain what the attenuated level was showing on this particular tape, but the attenuated level sets itself and should be the correct level -- I cannot adjust it.  That is what I'm trying to get at -- if the camera keeps the attenuated level correct so that it is not over-driven, why is the level distorting?  I cannot hear any distortion in the headphones when monitoring through the camera.  When I set levels manually in other situations, I can always hear if there is distortion and adjust accordingly -- does the attenuated level setting somehow bypass the headphones and keep me from hearing if there is distortion?  Any WHY is there distortion if the camera is supposed to set the correct level to adjust for a situation like this?

    Barb

  • 8. Re: Distorted Audio
    Studio X Level 7 Level 7 (26,940 points)

    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

  • 9. Re: Distorted Audio
    NLEdit Level 4 Level 4 (1,645 points)

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

  • 10. Re: Distorted Audio
    Barbara Smits Level 2 Level 2 (220 points)

    Dear NLEdit:

    I wonder if this could be some type of harmonic distortion?  The group of around 50 people is singing in various harmonies which reach great volume at times, plus the sound is echoing around a brick church interior -- I will try to post a sample soon -- don't give up on me just yet.  I did try the hum filter which corrects harmonic distortion, and I guess it did some good, but I also had to drop the volume dramatically and was too tired to try any longer last night.  I would like to get to the bottom of this, however, for future situations.  As far as investing in all of the new sound equipment out there and recording directly to computer, I am a one person studio, 68 years old, and the video business has dropped off so dramatically that I have no intention of investing thousands of dollars in new equipment at this point when everyone is intent on doing things themselves.  What I have found works best is a separate small digital recorder, completely separate from the camera, that can act as a back up.  I may invest in a more expensive one than I currently have, but it has saved the situation on several occasions in the ambient mic category!  Thanks.

    Barb.

  • 11. Re: Distorted Audio
    NLEdit Level 4 Level 4 (1,645 points)

    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.

  • 12. Re: Distorted Audio
    thrillcat editorial Level 4 Level 4 (3,840 points)

    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.

  • 13. Re: Distorted Audio
    NLEdit Level 4 Level 4 (1,645 points)

    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.

  • 14. Re: Distorted Audio
    thrillcat editorial Level 4 Level 4 (3,840 points)

    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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