Audio Sync tips when shooting in 24P

Update: December 7th, 2009

Audio Sync tips
when shooting in 24P

With an external audio recording device

by Scott Thomas
Director of Engineering
the Victory Studios

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There is a lot of questions regarding how to record audio separate from a HDCam camera and be able to sync it up later. Here are some thought that I have put together that may help clear up some of the confusion.

First, match the rates of the camera and audio device. If the camera is 24P, the audio device should be 30 frame Non-drop timecode. If the camera is 23.98P, the audio device should be in 29.97 Non-drop frame.

Second of all it is a wise idea to record audio on the HD tape as well as the external device. Ideally this would be the same audio that is feeding the external audio recording device (DAT, DA88, Nagra, DEVA, etc). Think of it as a great backup device.  At the very least, turn on the camera mic. This gives a locked sync reference for checking the sync in post.

Third, remember that the biggest issue that we are dealing with is the difference between 24 frame and 30 frame timecode. The camera records 24 frame timecode and most audio houses that I have talked to want the audio to have 30 frame timecode for mixing. The other issue is that for downconversion and offlining to be guaranteed frame accurate, the timecode on the camera must be continuous (ie Record Run). This means that you can’t just ‘Jam’ the timecodes together and let the devices free run.

So what should you do? Here are some options that have worked:

Option 1

Do nothing and let the post/sound house spend a lot of time (make a lot of money) syncing your sound up manually.

Pros:

easy to do in the field


Cons:

the bill

Option 2

Have a timecode slate that is displaying the timecode of the external audio recording device. At the beginning of every take, show this slate in the frame so that the time reference can be manually read off and used to lock audio in post.

Pros:

Non-Obtrusive to camera operations
Audio sync points can be entered when logging tapes


Cons:

Somewhat labor intensive in post


Option 3 (ideally combined with option 2)

Record the 30 frame timecode out of the external audio device onto one of the audio tracks of the HD tape while recording sound for sync checking (see above) on the other(s). In post, the audio device can chase this 30 frame timecode signal and sync up automatically.

Pros:

Minimally-Obtrusive to camera operation (timecode can be sent wirelessly to camera)
If using a disk based recorder (i.e. DEVA), there is almost no time syncing up in Post


Cons:

Option 4

Take the timecode (and in some cases the video out) of the camera and run it into a downconverter or timecode translator (i.e. Afterburner, Synch Box, Lockit). The converted timecode is then fed into and recorded on the audio device. What this does is convert the 24 frame timecode from the camera to 30 frame timecode on the audio device.  This has been the most trouble-free in post.

Pros:

Downconverted video available in the field (with downconverter)
Most trouble-free in post

Cons:

More Obtrusive to camera operation (more wires)
More wires and gear to hook up in the field
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