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Old Feb 14, 2012, 11:15 AM   #1
monokakata
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FCP X loss of one audio channel

I've run into an FCP X (or camcorder) problem that has me baffled. Maybe somebody can help me understand.

I'm shooting with a Canon XA10. Two mikes coming into the XLR connectors, and the XA10 is set to place each on its own track.

I was shooting a rehearsal for a performance, and whenever I looked at the XA10 audio display I noticed nothing unusual. Each channel had activity.

When I brought the clips into FCP X (the .3 version) all the clips but one had two separate audio channels, as expected.

FCP X displayed each channel as "Mono (channel-1)" or "Mono (channel-2)," as expected.

But one clip has only one channel, and that channel's marked as "<clip name> -a1."

The clip immediately before it has 2 channels, and the clip immediately after it also has 2 channels. The time between clips was only a matter of seconds.

If everything after the one-channel clip stayed one-channel, then I'd be looking to something I did, or something that failed somewhere along the line. But everything after that (and on other days, with the same mikes) was fine; always the proper two channels.

I grabbed a ClipWrap trial and converted directly from the .mts file, in case FCP X had somehow hiccuped on the import. No difference -- still just the one channel.

I haven't simulated an accidental mike disconnect (or level-set-to-zero) to see what FCP X does with a blank audio channel. I did re-import the clip, making sure that the "Remove silent channels" setting wasn't ticked. No difference.

I'll do more testing with the mikes and the XA10, but I have no memory of making any level or connector changes before the next clip, which, as I've said, is just fine. If I did something I can't remember doing, then I also undid it and can't remember doing that either. That seems unlikely to me.

The performance is in a few days and I'd be more relaxed shooting if I had a good idea about what went wrong on that one clip but on no other.

Any ideas?
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Old Feb 14, 2012, 12:26 PM   #2
Zwhaler
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All I can think of is that one of the mics experienced a connection issue during that clip and didn't record any audio. If you paused the recording during the shoot then started recording again when the mic stopped working, then that audio is lost. This may or may not help but when I'm filming and everything is going like it's supposed to, don't stop recording, you can always choose not to use footage but you can't go back and grab something that was lost.
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Old Feb 14, 2012, 12:32 PM   #3
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do you still have your media cards? Or did you reformat? Play back your clips on the camera to see if there is audio and watch the levels.
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Old Feb 14, 2012, 02:53 PM   #4
monokakata
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Thanks for the responses, you guys.

The problem with the "missing" audio wasn't that it was missing, but that it was embedded into a single stereo track.

I'm trying all possible combinations now. What seems to be happening is that under some conditions, FCP X believes that it's looking at a single stereo track instead of two separate mono tracks.

I can reproduce the problem some of the time but not always. It's confusing, but I'll keep at it.
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Old Feb 14, 2012, 04:04 PM   #5
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OK, got it. I was barking up the wrong tree (thinking about the XA10 and different mikes, and thinking that I had indeed lost one of my channels).

This link got me to the answer:

http://www.kenstone.net/fcp_homepage...ing_young.html

For some reason (probably markedly different volume levels on each track) at one point FCP X decided it was looking at a stereo track, combined the dual monos, and displayed only the single (stereo) audio track. Every other time, it "saw" dual mono tracks and did the right thing there.

What I didn't know was that it's easy to find the FCP X switch that says to display "stereo" or "dual mono."

In case I'm not the only one who didn't know, it's like this:

highlight any of your clips
use the inspector - audio
"Channel Configuration" will open
when it opens, you can select "stereo," or "dual mono," or "reverse stereo," if what you're seeing in the audio track isn't what you expect (or want).

But as soon as you click anywhere else in the FCP X display, you lose that possible selection, and even if you highlight the audio in the timeline, you can't get it back unless you re-click on the clip in the Event Library.

Not knowing this, I would choose a clip, right-click to place it on the timeline, and then all I could see for "Channel Configuration" was "Channels: Unsupported Clip."

Now as for why FCP X sometimes interpreted my clips as dual mono and sometimes stereo, I don't know.

But now that I know that what I was certain I'd done at the camera (dual mono) is indeed being imported as such, I'm relieved.

I'm prepared to be told that everybody knows this -- but I didn't.
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