camera audio & DAT audio out of sync, drifts

[Michael Gissing]

Matte, NTSC is not real time.It measures 30 frames every 29.97. The dat is real time so the drift is the same as the rate of time drift in 29.97. DF is the way to keep the frame count the same as real time, but it is a fudge.

On my sample rate converter, 47.952 is a standard preset that is used to correct this drift. If you are starting with 44.1khz, the magic correction is 44.056. I deal with PAL mostly, but we are aware of the problem as we deliver to you poor NTSC suffers

[Bouncing Account needs new email address]

[Joanie] “I tried exporting the CD audio track at 47.952 and reimporting, but it still drifts, It was 44.1 to start with”

That’s what I was aluding to in my previous message above (it was posted as you were posting THIS one.)

You want the DAT to the CD to be a perfect file conversion that results in a perfect one-to-one TIME MATCH.

If the DAT plays the track at 46 minutes and 31 seconds.
You need the CD to play at 46 minutes and 31 seconds.

[Joanie Spina]

Thank you…I sent that on to the audio guys. Will wait to here back from them.

[Bouncing Account needs new email address]

NTSC is perfectly REAL TIME in a closed system.

Otherwise if you recorded a clock, it would play at a different speed than the clock itself.

You’re getting caught up in the frame-rates.
They have nothing to do with TIME.

They are actually MEASURED by TIME.

A video camera scene recording for 22 seconds rolling at 25 fps (PAL) and played PAL will play for 22 seconds.

A video camera scene recording for 22 seconds rolling at 30 fps (NTSC) and played NTSC will play for 22 seconds.
Even though the two were recorded at different frame RATES (per second) as long as they are PLAYED at the same rate, they will be exactly the same LENGTH in TIME.

That’s why we say, “per seceond” instead of “per frames”.

[Mike Most — account bouncing, bad address]

Which direction is the drift? Does the picture get ahead of the sound over time, or is it vice versa? If the picture gets ahead (i.e., the sound gets behind) then the sound is running too slowly. My guess is this is the case, and my further guess is that the sound man pulled down the sound when he did the CD mirroring. This is normally necessary for a program shot on film due to the fact that telecine does not run at 24fps, but at 23.98 fps – so sound has to be slowed down accordingly. In your case, the production was shot on video, so no pulldown occurs in the picture. Therefore, the sound needs to be mirrored exactly as shot, with no pulldown.

[Bouncing Account needs new email address]

[Mike Most] “In your case, the production was shot on video, so no pulldown occurs in the picture. Therefore, the sound needs to be mirrored exactly as shot, with no pulldown.”

Bingo!

“Real-time” transfer to CD.

[Frank Nolan]

[Joanie] “The aif files are on an audio CD, 44.1
I shot on standard dv on a sony pd150, 48 khz samling rate, 16 bit”

That is the root of your problem. Have the audio guys burn a cd of aiff data files not an audio cd. Tell them to leave the files as the original 48k sample rate and just burn them as data to a cd. Then you just import the files into your FCP 48k session and it should match.