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Canon EOS Crop Sensor for HD
APS-C sensor cameras including the 80D, 70D, 7D Mk. II, 7D, EOS M and Rebel models for HD video recording.


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Old July 22nd, 2010, 08:52 PM   #1
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Audio Sync Issues

I have searched the forum...and found some info...but not what I really wanted.
A friend of mine shot with a 7D and recorded audio directly to the camera.

Some of the clips were in excess of 20 minutes long. When they took the clips DIRECTLY into post, they noticed that the audio sync would get greater...the further you went into the clip.

Is this a standard problem ? This is all I know about the project. I'm thinking about buying a 7D this week...and I'm concerned. I was looking at the Zoom H4 and assume I would not have issues (including auto gain) with this. But what if I'm recording 24p ? Does the audio sync with 24p footage okay ?

Thanks for any help !
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Old July 22nd, 2010, 09:01 PM   #2
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If he shot a 20 minute clip, it couldn't have been HD because you can't shoot more than about a 12 minute clip length when shooting HD with the camera. So there's some issue going on there, I don't know what.

I shoot 24p HD and record sound with a Zoom H4N. No sync problems at all.
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Old July 23rd, 2010, 07:25 PM   #3
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Bill...

thanks. How do you sync the audio from the zoom ? Good old film days....clapper/slate ?
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Old July 23rd, 2010, 09:51 PM   #4
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pluraleyes is your friend
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Old July 23rd, 2010, 10:19 PM   #5
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thanks Alex...but we're using an Avid Adrenaline system...on a PC.

Seems that software won't work for us.
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Old July 25th, 2010, 05:34 PM   #6
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I announce "Action" after I have both H2 and camera recording. After processing and trimming the audio from the H2 somewhat in Audacity I export it to WAV format and move that file to the folder my NLE can find it in.

Drag 'n Drop to the separate audio track on the timeline then drag it until the waveform peaks on the word "Action" match those of the same word in the camera's audio track. Drag it back and forth as necessary until you eliminate the echo effect and you have proper synch.

Trim the IN and OUT points on the timeline, mute the camera audio, and your set to go. Do the same with the next clip.
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Old July 26th, 2010, 10:05 AM   #7
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Kevin,

You won't get long clips remaining in sync without some drift....you are expecting two different 'digital clocks' to be frame accurate over a long period and this doesn't happen. To do this in a professional environment you would use timecoded cameras/recorders and lock theim to the same video reference 'video black' signal.
However it doesn't mean the camera and a separate audio recorder aren't the best way to go, Just use an audio/video mark, like a handclap to give you a starting sync point and be prepared to nudge either the audio or picture on the timeline after a few minutes, to keep the sync good.
Films were made for years and years before timecode arrived, with Nagra audio recorders that used a crystal that was only as accurate as todays digital clocks. But film cameras only ran for a few minutes anyway.
If I shoot a lonk event, I lay up my R-44 recorders audio first, then drop my Canon 5D2's pictures against that, using guide sound to match them. I also shoot simultaneously with a Panasonic GH-1 that allows very long takes (thankyou Tester13!) and I then have to make small tweaks to keep all three synced.
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Old July 29th, 2010, 07:40 AM   #8
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Singular Software now have DualEyes for NLEs other than FCPs PluralEyes.

Check your NLE and camera / dual system audio are all set to 48k sometimes 44.?? k gets involved somewhere and this will cause drift.
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