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Old February 15th, 2006, 10:24 AM   #1
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Drifting audio

Iīm editing a multi-camera shoot, done with four different cameras. JVC DV500, Sony VX2000, Panny DVX-100 and a Canon XL-1. (What a mix)

All tapes are captured through firewire using the JVC as a deck.
Audio comes from DAT and is synced in by hand.

Two Sony tapes and four Canon tapes shows up in the (FCP5) browser with odd audio sample freq. The Sonyīs at 47999,7 K and the Canon 48003,8K 48004K 48003,8K and 48003,6K

The sync between the cameras seem to be intact at all times, but the audio drifts slowly out of sync.

Whatīs the easy way out ? Stretch the audio? By how much?
Re-capture the odd tapes?

Any ideas?
Kristian Indrehus is offline   Reply With Quote
Old February 15th, 2006, 10:34 AM   #2
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This definitely is not my area of expertise, but couldn't you convert the sample type in an audio program so that all clips are consistent (such as 48000 Hz)? For example, with iRiver audio that is captured at 44100 Hz, I use Adobe Audition and simply import at 44100 Hz and then choose Convert Sample Type from the edit menu, selecting 48000 Hz. The audio retains the same pitch and duration as the original file and no longer shows any noticeable drift (at least in Premiere Pro) as it does when using the wrong sample type, even when over an hour long.
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Old February 15th, 2006, 10:53 AM   #3
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In my experience, the VX2000 doesn't have audio sync issues. The XL1, on the other hand, is notorious for it.

My question is why do you need the audio from all the cameras to be in sync? Why not just use the audio from one camera and sync it to the other three? In my opinion, it's much simpler than trying to use audio from all of them. FCP has excellent multi-cam capabilities and it will allow you to use audio from only one camera.

If you still need to sync the XL1's audio, then remember that it is in sync at the beggining, but after one hour, it will be 12 frames off, so you need to compensate for those 12 frames at the end while keeping the beggining as it is. I haven't found a way to do that without cutting out 12 frames and then just slipping the audio back to replace them. The problem is if you need the whole clip, you can't really cut anything out.

By the way, I actually shot a production last year with the exact same cameras as you, except I had an XL2 instead of the JVC. I promised myself to never do it again - the colour differences are just too great and I spent hours colour correcting. Were you able to match all the cameras? If so, how?
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Old February 15th, 2006, 11:20 AM   #4
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Quote:
Originally Posted by Andrew Khalil
My question is why do you need the audio from all the cameras to be in sync?
I donīt. I only need audio from the JVC for some ambience. The DAT audio is the main audio trackīs. But itīs drifting. I can slice it but I just hate not being able to trust the sync when switching between four cameras.


Quote:
Originally Posted by Andrew Khalil
By the way, I actually shot a production last year with the exact same cameras as you, except I had an XL2 instead of the JVC. I promised myself to never do it again - the color differences are just too great and I spent hours color correcting. Were you able to match all the cameras? If so, how?
Sort of, but not really. XL-1 is the worst of them. I use it only when I have to. The JVC stands out looking superior, so I use that one as much as possible. Itīs the front close-up so thatīs what Iīd do anyway.

Iīve shot two shows with this set-up. The first one was accepted for a nationwide DVD release, so I guess it wasnīt too horrible... though I thought it was. Not being lit for camera made it even worse. Well, I wonīt do it again. From now on Iīm shooting with three Canon H1īs. I just have to finish this second DVD release first.

Iīll try stretching the audio then.
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Old February 17th, 2006, 01:47 AM   #5
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For FCP Studio users. This is how I solved it.

1. Check in the timeline that the audio is sync at the beginning of the program.

2. Go to the near end (where audio is out of sync.) and offset the audio +/- frames until perfect sync is obtained. Keep track of how many frames you offset the audio before undoing it.

3. In the timeline, control click the audio and choose send to Soundtracks.
Soundtracks opens with the audio files.

4. Choose Time Stretch from the Process menu and choose frames in the pop-up menu. Now tap the same number of +/- frames and click OK.

5. Soundtracks starts processing. (Iīm not sure if it was because of my 1,5 hour long stereo file, but you actually canīt see anything happening) When processing is done,(you just have to guess and try) save using apple S and the new file is saved and automatically updated in FCP. Now in perfect sync all through the program.
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Old February 22nd, 2006, 11:17 PM   #6
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Interesting, since sample frequency has nothing at all to do with sync. It is just that, the frequency of the audio sample 44.1, 48, 96, 192 or otherwise. The problem you have is probably tied to df vs ndf issues. It's important to make sure that all the cameras agree on timecode before you start, df or ndf, and pass those settings on to your sequence. It's also nice to have a DAT that uses smpte TC. The canon is probably the worst of these beacause it gives you the rope to hang yourself with(TC options)as well as being 9 years old, dissing it it like dissing the Atari 2600. Good Luck, Jason.
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Old February 23rd, 2006, 01:18 AM   #7
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It looks like the multi-clip based itīs sync on a clip with weird timecode.
So when all the other cameras sync to that, the DAT drifts more then expected.
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