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Recorded audio is slightly longer than camera audio

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Wesley Dysart
Recorded audio is slightly longer than camera audio
on Sep 10, 2009 at 6:59:22 pm

I shot an hour long keyboard performance and I'm having a problem.

The audio was recorded direct, into Cakewalk Sonar at 64-bit, 44.1khz, then exported as 24-bit 44.1khz.

I brought this into Final Cut Pro along with the DV video. I'm trying to sync the audio but the recorded audio is about 8 seconds or so longer than the DV audio. So I'm having to time compress the audio to make it be in sync, but this is causing phase issues.

I've tried using QuickTime to export the audio as 48khz., but it doesn't affect the length.

any help is much appreciated.

-Wesley D.


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Ty Ford
Re: Recorded audio is slightly longer than camera audio
on Sep 10, 2009 at 11:38:09 pm

Hello Wesley and welcome back to the Cow Audio Forum.

There's an old oriental saying, "Man with one watch always knows what time it is. Man with two watches never does."

In this case your audio was recorded on systems without syncing them. While you can sometimes get away with it, there are times (like this) when you can't. My best solution is to keep trying time compression on the long one until you hit the right number and get close enough.

Maybe do the math. If you're 8 seconds long after 60 minutes, what percent of 60 minutes is 8 seconds.

Maybe there are open spaces in in the hour where you can tighten the long track enough to make it work for a while.

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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Wesley Dysart
Re: Recorded audio is slightly longer than camera audio
on Sep 11, 2009 at 12:59:29 am

Thanks for the advice. The time adjustment thing is really freaking me out. I can line up the beginning and the ending, but there is still drift in between. Correcting for the end pushes the earlier parts ahead of where they should be. Then adding time back to the early parts pushes the later parts out of time. If there is a magic setting it's at a decimal place that's less than 1 frame.

I'm able to get single songs to work, but it's an ungodly amount of work considering I thought I'd be able to line up the beginnings and have everything fall into place. With this problem even a slate or a tone pop wouldn't help, as somehow the audio is literally at a different speed.

How do they film live bands? Usually they'll want the audio to come from the mixing board. I've done some sync before where I lined up a beep with a red flash on the screen, then everything fell perfectly into place. would you need a camera that can send or follow sync from a workstation? I've seen film sync with analog tape, if that works why on earth would digital be drifting so badly?

Is it typical for MiniDV camcorders to run a bit fast or slow? I was thinking in the digital domain 60 seconds should be 60 seconds. I'm alarmed to think that either my audio workstation or my camcorder is running fast or slow. The audio workstation is clocked to an ADI-2 via ADAT, so if anything I'm thinking it's the video camera. I was hoping this would just be a sample rate thing. I can't seem to find a way to alter the sample rate and have it affect the length. Everything I try seems to want to preserve the length...

-Wesley D.


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Ty Ford
Re: Recorded audio is slightly longer than camera audio
on Sep 11, 2009 at 1:10:02 am

"Thanks for the advice. The time adjustment thing is really freaking me out. I can line up the beginning and the ending, but there is still drift in between. Correcting for the end pushes the earlier parts ahead of where they should be. Then adding time back to the early parts pushes the later parts out of time. If there is a magic setting it's at a decimal place that's less than 1 frame.

> Yup. You'll have that sometimes.

I'm able to get single songs to work, but it's an ungodly amount of work considering I thought I'd be able to line up the beginnings and have everything fall into place. With this problem even a slate or a tone pop wouldn't help, as somehow the audio is literally at a different speed.

> Yup and if you had used another recorder, you might have lucked out...or not.

How do they film live bands? Usually they'll want the audio to come from the mixing board.

> Just as you have with two circuits that are closer in time than you're trying, or they use a master clock for both audio and video to lock to. Sometimes wordclock.

I've done some sync before where I lined up a beep with a red flash on the screen, then everything fell perfectly into place. would you need a camera that can send or follow sync from a workstation? I've seen film sync with analog tape, if that works why on earth would digital be drifting so badly?

> minute (small) differences in the individual clocks.

Is it typical for MiniDV camcorders to run a bit fast or slow? I was thinking in the digital domain 60 seconds should be 60 seconds. I'm alarmed to think that either my audio workstation or my camcorder is running fast or slow. The audio workstation is clocked to an ADI-2 via ADAT, so if anything I'm thinking it's the video camera. I was hoping this would just be a sample rate thing. I can't seem to find a way to alter the sample rate and have it affect the length. Everything I try seems to want to preserve the length... "

>>Hm, Pro Tools has time compression/expansion.

Regards,

Ty Ford



Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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John Fishback
Re: Recorded audio is slightly longer than camera audio
on Sep 11, 2009 at 9:20:22 pm

Ty has it right. You must sync the audio workstation with the camera. Most pros do this with video ref which is sent to all cameras and the audio workstation (which is then resolved to word clock). Our Pro Tools system has a box called the Sync IO. Its job is to keep audio and video signals in sync. Over an hour, sync will drift if you haven't locked the devices together. It's subtle-2 tenths of a percent in tiyr case. The miniDV isn't running fast or slow. It's drifting slightly. Pro Tools can expand and compress time. Cakewalk can probably do the same. In fact, Soundtrack Pro in FCP can also probably do it. Try one of those.

John

MacPro 8-core 2.8GHz 8 GB RAM OS 10.5.5 QT7.5.5 Kona 3 Dual Cinema 23 ATI Radeon HD 3870, 24" TV-Logic Monitor, ATTO ExpressSAS R380 RAID Adapter, PDE enclosure with 8-drive 6TB RAID 5
FCS 2 (FCP 6.0.5, Comp 3.0.5, DVDSP 4.2.1, Color 1.0.3)

Pro Tools HD w SYNC IO, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec Monitors, PrimaLT ISDN


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Thax Clave
Re: Recorded audio is slightly longer than camera audio
on Sep 12, 2009 at 12:11:26 am

[John Fishback] "Over an hour, sync will drift if you haven't locked the devices together. "

I've shot hundreds hours of non-synced footage over the years.
Mini DV, DVCAM, Digibeta.

Multiple cameras, rolling totally independently, some on battery power, some on AC supplies.

Audio sourced and synced-up from a board recording on MD, CD, DAT.

I simply never have problems with "drift."

I telling you, I do this ALL the time.

I just shot that way today.

I used 3 camcorders (a Sony, a Canon, a Panny) all rolling on the same stage play.

I can capture each tape, and then use multi-cam or simply lay each capture on a different video track.

They remain in sync for the entire roll (about 45-75 minutes, depending on what play I am recording.

I'm betting the presenting problem is in the CONVERSION of sample rates from the Audio station.

This should not be a problem, as otherwise, most "multi-cam" edits would be nearly impossible.






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Andrew Commiskey
Re: Recorded audio is slightly longer than camera audio
on Sep 20, 2009 at 1:45:23 am

Try exporting from cakewalk at 48k 16bit if possible. I have had instances when I converted 44.1 to 48 K and brought the files into FCP and the tracks were slowed down. something to do with markers etc. If you cannot access cakewalk try soundtrack Pro and convert sample rate and bit depth. 24 bit audio in a DV timeline can sometimes cause a problem.
Just some ideas.
Drew


Chaos is the beginning of everything.


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Bob Cole
Re: Recorded audio is slightly longer than camera audio
on Sep 28, 2009 at 7:26:45 pm

[Thax Clave] "I'm betting the presenting problem is in the CONVERSION of sample rates from the Audio station."

I agree, and I hope that when you find the solution, you'll share it, because on rare occasion I've received material recorded at oddball rates.

You may want to take this question into the FCP Forum. I suspect that you could make an adjustment to your FCP project that would solve the problem.

Bob C


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Wesley Dysart
Re: Recorded audio is slightly longer than camera audio
on Sep 28, 2009 at 9:48:46 pm

Since this wasn't a major project I just time stretched the audio inside Final Cut Pro. I think the main issue is that I recorded at 44.1 instead of 48khz.

It seems most people want to maintain length when converting sample rates, so a simple sample rate conversion wasn't helping. The audio was longer than the video which would make sense if it was recorded at a slower speed then imported while preserving length.

Thanks for your help guys! Next time I do a video I'll let the board know how it goes!

-Wesley


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