Audio Sync Issues with Single system recording

[rhetorik]

I recently had a gig where we recorded audio straight into the camera and the editor told me that the audio ended sooner than the video.

Is it even possible to record audio and video at different frame rates when its single system?

Cameras were Panasonic HVX200 and HPX170.

Thanks

[nosys70]

probably what he means is there is some missing audio at the end ?
or he made the common mistake to record with the wrong frame rate , 29.xx instead 30fps ?
Or you used AVCHD that can be sometime tricky to read on some machine ?

[dre83]

Also watch out you're viewing it in sync.

A two-pop is very usefull to check this. Make a countdownclock from 10 till 0.

On the number "2" you put a 1000Hz sinus of exactly 1 frame.

Now watch and see if the sound is just when the 2 comes up. Or you can also put something else which is very attractive (like 10 seconds black and on the 2nd second one white frame)

[rhetorik]

thanks for the input but what confuses me the most is how can a camera record its video and its audio out of sync? If I were recording audio onto a seperate recorder I can see how this can happen but if your audio is running straight into the camera how could this happen?

[Gohanto]

If there's a bug in the camera firmware it can happen.

Also, check to see if the audio is actually out of sync (does the slate clap line up visually and audibly), or if the audio just ends before the video does.

[rhetorik]

yea Gohanto I think it is a bug just because there were only a few clips that turned out that way and I also had a back up recording onto my 744T and when I gave them those files they said it worked fine...

weird.

[Noiz2]

thanks for the input but what confuses me the most is how can a camera record its video and its audio out of sync? If I were recording audio onto a seperate recorder I can see how this can happen but if your audio is running straight into the camera how could this happen?

Well doing a lot of post I have seen this before.
The original DVX100 send audio out the FW 1 1/2 frames out of sync with the picture. Picture editors usually don't notice. Any footage that is at a true X.0 frame rate (24, 25, 30) that gets imported into FCP (if FCP has not been setup properly) will cause FCP to re-stamp sound coming in at the wrong sample rate and cause a drift. Depending on the system audio maybe clocked differently than the video and not nec. in sync. This used to happen a lot with a audio interface set up for digital sync but with the digital cable either not connected or connected to a box that was switched off.

Also if his system has a "pull down" switch, he could have that in the wrong position. It will clock the audio at a special rate so that it will stay in sync with telecine'd footage.

and FYI audio doesn't have a frame rate. TC is only used as a start position. Digital audio is clocked to a word clock either internally or externally. And that word clock doesn't have any real relationship with the frame rate of the TC. It's sort of obvious when you consider that the finest resolution of TC is the subframe (so 1/100 of a frame, 2,997/sec (NTSC)) and the word clock has to be at least as high as the sample rate (48,000/ sec) and some use a "super clock" at 256X (12,288,000/ sec.).

Analog tape could be synced with TC but that is WAY too slow for digital.