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Old December 14th, 2006, 04:35 PM   #1
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Questions about syncing audio with video via digital field recorders

Ok so I have several questions about syncing audio with video, as well as a digital field recorder. For starters I've only done syncing with film via DAT Recorder, and was a bit unsure about the process with video, since I'm use to being tied into the camera's xlr inputs.

I understand that audio is synced with video via blackburst generator, however I was confused about this process. Does it need to be synced prior to shooting or can it be synced via genlocked in post? Also If I need to sync it with the camera, does it require that I hook the digital field recorder into the camera for the duration of shooting, or do I just hook it up and calibrate so they both operate on the same timecode?

My other question is about the TASCAM HD-P2 field recorder. I know it has a built in black burst generator, as well as has various setting to match the frame rate of the video camera (i.e. 29.97, 23.976) etc. However, if I were to just set the field recorder to the correct video framerate could I just sync it manually in post by matching the sound of a slate with the video?

Sorry for all these questions, I'm a recent film grad, and the most exposure to field recorders I had was either minidisc or DAT recorders. I was looking at digital field recorders and the TASCAM seemed best for video production. I had looked at several of the Marantz units but read that they had a discernable mic preamp hiss

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Old December 15th, 2006, 12:22 AM   #2
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Quote:
Originally Posted by Chris Hanyok
Ok so I have several questions about syncing audio with video, as well as a digital field recorder. For starters I've only done syncing with film via DAT Recorder, and was a bit unsure about the process with video, since I'm use to being tied into the camera's xlr inputs.

I understand that audio is synced with video via blackburst generator, however I was confused about this process. Does it need to be synced prior to shooting or can it be synced via genlocked in post? Also If I need to sync it with the camera, does it require that I hook the digital field recorder into the camera for the duration of shooting, or do I just hook it up and calibrate so they both operate on the same timecode?

My other question is about the TASCAM HD-P2 field recorder. I know it has a built in black burst generator, as well as has various setting to match the frame rate of the video camera (i.e. 29.97, 23.976) etc. However, if I were to just set the field recorder to the correct video framerate could I just sync it manually in post by matching the sound of a slate with the video?

Sorry for all these questions, I'm a recent film grad, and the most exposure to field recorders I had was either minidisc or DAT recorders. I was looking at digital field recorders and the TASCAM seemed best for video production. I had looked at several of the Marantz units but read that they had a discernable mic preamp hiss

THANK YOU
Not an expert but I'll give your questions a shot.

There's two kinds of sync to think about, timecode sync and sample rate sync. There's the timecode the camera and the audio are both recording so they each have their Time of Day clocks for that purpose. They each also have sample rate clocks that control, well, the sampling of the signal in the A/D conversion process. If the sample rate clocks of the camera and the audio recorder are running at slightly different rates, a shot's audio is going to run slightly slower or faster than its video so if you slate the shot and line up the slates in your NLE, the audio will slowly drift out of sync over time. Blackburst sync or genlock locks the two sample rate clocks to the same timebase so this doesn't happen - with blackburst the audio recorder locks its sample clock as slave to the camera as master while with genlock they both are slaved to a common master clock. For most practical purposes this isn't too much of an issue these days as most current gear has clocks that are very accurate and will be close enough to each other that drift over, say, a 15 minute shot will usually only be a frame or two, easily corrected for in the editor. Note that the blackbust clock doesn't transmit any time of day information.

Syncing timecode means setting the timeline or TOD clocks in the various pieces of gear to read the same value so the timecode recorded with the audio is the same as the timecode recorded with the video. This doesn't prevent drift with in the shot - instead it provides a convenient way of insuring the right audio is mated to the right picture and to line them up in the editor. With film, the audio recorder is usually the master and sends code either to a smartslate, insuring the slates displays code that is identical to code the recorded with the audio or code is sent to the camera to set its clock (where there is one), or both. There are various ways to set it up, so that the code is either fed continuously from the master to the other devices or it's 'jammed' to set them together and then they're allowed to run on their own. With video it gets a bit more complicated - with broadcast cameas usually the camera is the master and the audio recorder is either sent code continuously from the camera or is jammed to the camera's clock. But it could go the other way as well and audio could send time to the camera. There are so many variables with professional cameras and recorders that Wolf Seeberg has written two entire books on timecode techniques for various types of shooting and cameras. But all of this is a problem with prosumer DV cameras only a very few even *have* timecode I/O. You could go film-style and send code from the audio recorder to a smartslate but what's most often done is just to use a plain old fashioned clapper slate and line it up in post.

AFAIK the Tascam recorder does not have any timecode or blackburst output that can send code to a camera or external device. It will read LTC timecode sent to it and will set both its internal timeline clock and sample cock to it and it can also sync its sample clock to incoming blackburst or wordclock. File based audio recorders like the HDP2 don't record timecode continuously along with the audio like you may be accustomed to with a DAT - instead they use code to timestamp the start time of the audio in the file header but that's the only time reference that is recorded.
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Old December 17th, 2006, 05:53 PM   #3
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Ok that helped. So then I could record audio separate, not plugged into the camera, and so long as I capture the video into the editor correctly, then it should sync up.
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Old December 18th, 2006, 04:24 AM   #4
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Originally Posted by Chris Hanyok
Ok that helped. So then I could record audio separate, not plugged into the camera, and so long as I capture the video into the editor correctly, then it should sync up.
It depends on the recorded/camera combination but miniDV and file-based recorders usually will hold sync for a reasonable length of time, especiually since the better editors let you stretch or compress the audio time slightly. Be sure to slate your shots with a clapper to make it easier to line them up and it's handy if you can get both head and tail slates to give you a reference mark at both ends.
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Old December 18th, 2006, 09:42 AM   #5
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For additional help in staying organized, an inexpensive capture program like ScenAlyser Live will add the date and time of day to the name of captured DV clips automatically. This can be very useful for DV cameras that don't allow you to set your own timecode and this information comes from the camera's time-of-day clock, separate from the timecode that's also captured in the traditional way. If you have several simple DV cams, you can still synchronize their clocks for organization even if you can't set their actual timecode. Then use the traditional slate method for tight sync.
If your audio recorder has firewire output, then capturing should work the same way, but I haven't actually captured with a newer audio device with firewire.
At any rate, organization rather than actual sync is usually the biggest problem with a major double-system project as long as you use some sort of slating method and guide audio on all devices. And as Steve said, there are so many different models of camera and audio recorder that it is difficult to be more specific than that.
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