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Brian Murphy
Don't know why this worked?
on Jun 4, 2012 at 1:11:32 pm

I got footage from a corporate event that was recorded on a AJA Ki-Pro drive and dumped it into final cut pro 7. Put the footage on the timeline and noticed that the audio in the footage was very very low. Just barely hitting. I highlighted the video track and two audio tracks and then selected link and stereo pair in the top menu bar. After doing this the audio tracks were coming in on normal levels.

I just don't understand why that boosted the sound with out noise or distortion? Were my project settings just setup incorrectly?


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Neil Patience
Re: Don't know why this worked?
on Jun 4, 2012 at 2:04:18 pm

It sounds like your audio channels were recorded out of phase.
So when you mono them they cancel eachother out, hence the low level.
When you pan them left/right for stereo the cancelling effect no longer happens so the level appears more normal.

Depending on what you have recorded on what track you may be better off just using one or other as otherwise you may hit upon this issue later.

Or you can try phase reversing one of the tracks if you need to keep both.

best wishes
Neil
http://www.patience.tv


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Bret Williams
Re: Don't know why this worked?
on Jun 4, 2012 at 3:02:23 pm

I always understood it to be reversed wires on the mic or recording device. Similar to hooking up one of your speakers on your stereo backwards. Speakers make sound going in and out. So if one signal is backward it works fine on its own, but mix the two as mono and one signal is telling the speaker to go out, and the other in, then you get nothing.

First time it happened to me it was a music track with extreme stereo separation. The only thing panned center was the voice. So the voice vanished. But the guitar, drums' etc were all separated and so they didn't cancel each other out.


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Neil Patience
Re: Don't know why this worked?
on Jun 4, 2012 at 3:30:50 pm

While wiring can be a cause of phase issues there are many more reasons why this might happen.

This article pretty much covers it.

http://www.soundonsound.com/sos/apr08/articles/phasedemystified.htm

best wishes
Neil
http://www.patience.tv


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Shane Ross
Re: Don't know why this worked?
on Jun 4, 2012 at 2:06:35 pm

Phasing. An odd issue that happens with audio sometimes where two audio channels cancel each other out.

Shane
Little Frog Post
Read my blog, Little Frog in High Def


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Tim Wingert
Re: Don't know why this worked?
on Jun 4, 2012 at 4:31:26 pm

So, when you highlight 2 audio tracks and select "Stereo Pair", it essentially hard pans left/right respectively?

Also, if the incoming audio was 2 channels out of phase, would this be noticeable to the person monitoring the record at the KiPro? (Either on the levels meter, or in the headphones?)


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Neil Patience
Re: Don't know why this worked?
on Jun 4, 2012 at 6:37:56 pm

[Tim Wingert] "
So, when you highlight 2 audio tracks and select "Stereo Pair", it essentially hard pans left/right respectively?"


Yes making a stereo pair will default to left/right panning.

[Tim Wingert] "would this be noticeable to the person monitoring the record at the KiPro? (Either on the levels meter, or in the headphones?)"

Its not always easy to spot this kind of error without proper monitoring equipment that shows audio phase, or the ability to simply sum or mono the tracks when monitoring. Headphones plugged into the camera would likely be in stereo so would probably mask this kind of error. Possibly could have picked it up if monitoring via a mixer that allows mono-ing of the monitoring.

If one side was totally phase reversed then you can more easily hear that in headphones or speakers but lesser degrees of error are harder to notice.

best wishes
Neil
http://www.patience.tv


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Michael Gissing
Re: Don't know why this worked?
on Jun 4, 2012 at 10:56:30 pm

And you can't leave it just as panned to fix the problem as any time it is played it might be as mono and the sound will disappear again.

With that much cancellation, it is likely the source is mono so unlink, pan back to center and pull the level right down on one track. You can leave it there in case you end up going to a sound post place that can fix the phase error.


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