PAL to NTSC Audio Sync Issues

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Level 2

210 points

PAL to NTSC Audio Sync Issues

Hi All,

I've searched through the forums and have found some similar issues but nothing exactly like this.

I am editing a music concert that was shot in PAL. The audio was also recorded separately and has been edited and mixed in ProTools.

When I take the exported audio and put it into my PAL timeline, it drifts out of sync with the video as expected. My questions are:

1) How should the audio be exported to match up to my PAL timeline?

2) When we convert to NTSC, I will use the Nattress filters for video, but what do i need to be concerned about re: the audio?

Thanks big time,
Jason

G5 Dual 2.5Ghz, 23 Cinema HD Display, Mac OS X (10.4.9), FCP 5.1 Studio

Posted on Mar 29, 2007 11:56 AM

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Answer 1

Mar 29, 2007 12:57 PM in response to JF138

Take the highest quality form of the audio track there is. Ideally this would be 24-bit.

Find out exactly by what percentage (to at least 4 places) it's off in each timeline (NTSC and PAL), although it should be the same. Do this with sync points near beginning and end along with a bunch of math. You can figure that out.

Stretch or shrink the audio track by that percentage for each track.

Line it up and you're done. Or the math was really bad and you start again.

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Answer 2

Mar 29, 2007 2:05 PM in response to Steve Braker

If you have sync pops at the start and end, you can use Fit to Fill to automatically speed-adjust the audio to fit your video.

Once you have the audio synced correctly in the PAL version, you may find the simplest way to convert to NTSC will be to re-conform a quicktime movie of the finished piece from 25fps to 23.98 using cinema tools. This will preserve the syncing work you have done, and allow you to work in a 24p ntsc timeline, which is good if you are going to DVD.

Hope this helps

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Answer 3

JF138 Author

Level 2

210 points

Mar 29, 2007 3:50 PM in response to Steve Braker

Hi Steve, thanks for the reply.

However, here's the thing - the audio CANNOT change. if anything has to be changed, it would be the video to conform to the audio.

Would I basically do the same thing here, just modifying video instead of audio?

Thanks,
Jason

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Answer 4

JF138 Author

Level 2

210 points

Mar 29, 2007 3:53 PM in response to Max Average

Thanks for the info. I cannot change the audio though - only the video (although I'd sure prefer not to).. Are there any ways to sync this up besides stretching audio or video?

If the length of time of the program doesn't change when you convert PAL -> NTSC, how is that the audio doesn't sync up easily??

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Answer 5

Mar 29, 2007 4:47 PM in response to JF138

Well, it would be a very unusual thing to do, and it would likely affect the quality of the video. But you could do that.

If it's an edited piece and not much drift, you could do it by removing single frames at strategic edit points. A lot of work.

Just out of interest: who's going to know if you change the length of the audio by 1.85679 seconds?

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Answer 6

Mar 29, 2007 5:24 PM in response to Steve Braker

Who's going to know? Anyone with perfect pitch. Anyone who may feel like picking up a guitar and strumming along with the concert.

What are the properties of the audio files that were given to you? Are they 44.1Khz or 48khz?

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Answer 7

JF138 Author

Level 2

210 points

Mar 29, 2007 5:36 PM in response to Steve Braker

Here's what I don't understand - some guys captured this concert in two ways - a PAL camera (and associated audio) and then some sort of audio recording, a believe a DAT.

They gave us PAL tapes which we have captured, and then ProTools audio files. Theoretically everything should match up at this point (the audio from the cameras and the audio from the recorder should be the same, right?)...

Why would it be that after changing the MIXES (but not shortening or lengthening the audio), exporting from ProTools, and then laying them into the FCP track (syncing up to the first beat of a song, etc), they audio drifts? Not bad, about 1 1/2 seconds in 6 1/2 min of footage.. but nonetheless, this is a HUGE pain.

Given this is a music DVD and the artist is a major musical stickler, changing the audio has a ZERO percent chance of being acceptable...

Thanks again for your help -
Jason

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Answer 8

Mar 29, 2007 5:34 PM in response to JF138

One more time.

What format are the files they delivered, 44.1Khz, or 48khz?

You mentioned DAT, which would lead me to believe they might be 44.1Khz.

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Answer 9

JF138 Author

Level 2

210 points

Mar 29, 2007 5:37 PM in response to thrillcat editorial

48k, 16 bit

Also tried 96/24 and 44.1/16, they all line up perfectly with each other but not with the video (or the audio that came from the video source)....

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Answer 10

Mar 29, 2007 5:37 PM in response to JF138

If they were recorded on DAT, they were originally 44.1Khz files. Ask how they got them to 48Khz.

If they merely did a "save as," they altered the length. If they did an actual Resample and then save as, we'll look elsewhere for the problem.

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Answer 11

JF138 Author

Level 2

210 points

Mar 29, 2007 7:31 PM in response to thrillcat editorial

Turns out they were recorded directly into ProTools as 96k/24bit.... Added into a 96/24 protools session..... exported as 96, 48, 44.1, all of them have drift....

Thanks again for all your help.

Jason

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Answer 12

Mar 29, 2007 8:15 PM in response to JF138

Not bad, about 1 1/2 seconds in 6 1/2 min of footage.. but nonetheless, this is a HUGE pain.

That's .4% - 1/250th... one sample in 250. Your musical genius may think they can hear that but I bet they never will - especially if the pitch is maintained at the same time as the speed change. I wouldn't be surprised if that's within the normal variation of DVD players anyway.

In any case, that's one frame about every 4 seconds...

You can find ways to take care of it or you can blame somebody else - depending which is mroe fun.

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Answer 13

JF138 Author

Level 2

210 points

Mar 30, 2007 3:36 PM in response to Steve Braker

Yeah they're doing a .41667% (if i recall) pulldown on the audio and we'll see if that works. It's starting to look like it was an NTSC audio session somewhere back in the chain so we have to adjust somehow...

Thanks,
Jason

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Answer 14

Mar 30, 2007 7:18 PM in response to JF138

Nothing short of an atomic clock is absolute. That's why for real true sync you still have to genlock cameras and recorders. If you don't even the same model cameras will drift from each other (though much less than you're seeing). Having that much drift between video and and audio system that doesn't have any understanding of video (or sync lock) isn't surprising at all.

Fortunately it's a heck of a lot easier to fudge now than it was 15 years ago.

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Answer 15

Apr 2, 2007 10:25 AM in response to JF138

Standard digital audio uses a 29.97 fps drop-frame time standard, either 44.1 or 48k. PAL video is 25 fps.

If you are going to end up in NTSC video anyway, why not convert the PAL video to NTSC at 29.97df and then edit that? The audio should sync up with video that uses the same frame rate. It's the old FCP editing time base thingie.

If you are attempting to sync by the numbers, different frame rates will cause you heartache. Also a problem if you are trying to mix drop frame with non-drop frame timecode at the same frame rate.

Get some video and some audio at the same frame rate and see what happens.

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