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That Syncing feeling
I’m currently producing a feature film using the Canon 7D and cutting it on Vegas pro. One thing baffles me and I hope someone can shed some light on this. As we are recording audio on a separate system, I need to sync a new audio track to the video clip. The 7D also records a track which is a great audio reference. We are also using a clapper board for the spike sound and the visuals. My issue is that when I zoom into the waveform, the spike from the clapper appears to be one frame out from the actual visual of where the two pieces come together. So I’m unsure whether to sync to the reference 7D audio track or to sync to the visual clapper hit. Could the 7D record one frame out of sync? The sound seems to be one frame ahead of the visuals.
You can see my current trailer here: https://www.youtube.com/watch?v=qzXKT6M870Q
Filmmaker http://www.sixlovers.com
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3 Replies
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Joel, I had this issue just today. I had a slight ‘ghost’ audio, but when I bumped the H4N track up a frame, the ghost disappeared. (Why the H4N spike would be one frame off I have no clue.) So my experience is to use the spike to get in the ballpark, and then finalize it by ear. That may be wrong, but it worked for me.
There is a product called ‘Pluraleyes’ that now works for Vegas. It is supposed to be really helpful in situations where you cannot get clap board spikes (such as press conferences), or when you have a lot of different tracks to synch up.
I wonder if Pluraleyes has an issue with the clap board spike being a frame off, or if it overrides the clap board spike based on the rest of the waveforms. I think they have a free trial, if you want to try it.
Norman Willis
http://www.nazareneisrael.org -
It looks like more than one frame out by the youtube vid. I would select both the audio and video tracks, hit the “U” key to unlock them and move the spike to the clap hit and see what that looks like.
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Could the 7D record one frame out of sync? The sound seems to be one frame ahead of the visuals.
That is extremely odd. How can the audio be recorded before the video? If anything, the audio should be after the video because sound travels slower than light.
Light travels approximately 186,282 miles per second so for all intents and purposes, it is instantaneous.
Sound travels 1,125 feet per second. Using the 7D’s 24p mode video is recorded at 24 frames per second. Since both measurements are in seconds, if we divide 1125 feet by 24 frames we get 46.875 feet per frame. That means that sound travels proximately 47 feet per frame at 24p. If anything, for every 47 feet that the microphone is beyond the audio source, the audio should be 1 frame behind. So if the camera were 94 feet from the source you should see the audio lag by 1 frame.
Perhaps the time it takes for the 7D to process an HD video frame compared to the time it takes to process audio causes the audio to be recorded earlier? (and maybe a “real” camcorder would compensate for that but the 7D is not a camcorder)
I would sync the audio spike to the visual clapper board.
~jr
http://www.johnrofrano.com
http://www.vasst.com
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