Steve House |
February 9th, 2008 09:28 AM |
Quote:
Originally Posted by Bill Ravens
(Post 823129)
One more time...
TC won't help you sync a seperate audio recording to your camera.
The 7xx series SD recorders are timed with WORDCLOCK. The fact that the 7xxT has a TC generator is almost an artifact, it still syncs itself to its internal WORDCLOCK. The problem is how to convert the wordclock pulse into something the camera can use and lock its TC generator to. Unlike LTC, Wordclock is simply a pulse with no absolute start or stop value.
Once again, the easiest thing to do is use a clapboard at the start, line up the audio and the video to the clapboard in post, and stretch/shrink the audio in post to account for drift.
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All very true - in fact I wrote Sound Devices tech support and asked if the audio sample rate clocked itself off of incoming timecode when the recorders were supplied with external code and their response was they do not. But its internal TC clock is derived from its audio clock and is highly accurate. That's one reason they suggest using the recorder as the timecode master.
The only time TC will help with a camera that doesn't have timecode I/O and genlock is if you use the recorder as master and send LTC to a camera audio track, then when you import the video clip you instruct the NLE to align the clip into the timeline using the recorded LTC and ignore the TC recorded with picture. Then when you drop the BWF from the recorder into the timeline it will align itself to the LTC. Unfortunately the only editors I've heard of that can read LTC and align to the timeline based on it are Final Cut Pro and Avid and if we're not using either of them recording the LTC is pointless.
You can also jam a smart slate and when importing the cip into the timeline, align the timeline with the numbers shown on the slate, then when you drop the BWF onto the timeline it will autoalign. But unless you have a h*ll of a lot of clips to sync, that seems like an awfully expensive alternative to just visually finding the frame where the sticks of an old fashioned slate bang together and lining it up to the spike on the audio waveform.
You are also absolutely right that unless you can slave the video sync on the camera to the wordclock on the recorder or vice versa nothing you do with the timecode does anything to preserve sync over long shots. At best all TC can do is help with the initial alignment but when you move away from that alignment point, sound and picture will eventually drift out of sync unless the audio and video clocks are slaved to each other. How fast they'll drift out depends on the quality of the clocks - with some cameras you might get away with an hour before you're a frame off but with others it might only be 5 minutes.
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