Pull Up/Pull Down and digital transfers

[dmfisher1]

I want to talk specifically about sample rates and digital transfers from one machine to another. I am in post for film and constantly dealing with these issues. I recently talked to a Sony tech and he told me that any machine locked to video sync is really running at 47.592kHz SR, not true 48kHz. Now I've heard of people recording production sound at 48.048kHz (pull up), so that when they pull down, they get true 48k and can accomodate digital transfers. But if the video machines are really running at 47.592, this should produce jitter and digital artifacts, right?
I'm doing some tests right now, trying to reproduce those errors so I know what causes them and how to avoid them. But I can't seem to reproduce the problem. Any thoughts out there?

[viaspiaggia]

yes everything you learn about frames rates and pull ups and downs changes in our modern world of (nearly-)all-digital production.

the important question for me is "what sample rate is the avid/fcp running at?" i always assumed, after learning all about pull downs etc, that an avid would be playing at 47.952 as you suggest. but i just did two features coming from an avid (one shot on film and one on 24p dv advanced) and in both cases the omf and the video transfer (vhs and beta sp) synced when running my pt at 29.97 with NO pulldown, ie true 48,000 samples. all these productions have gone back to the avid with no problems. my concern NOW is that when either of these get put to film to be projected, will a transfer house assume my file is at 47952?

i was hoping georgia's black hole post would get into this area (sync and some telecine) but it never did. i understand the basics, but would love to know EXACTLY what happens on the way to film, ie what type of box? analog inputs? how is it synced? etc... i'll add a post over on that thread and see if anyone bites!

-adam-

[trakbytes]

...a Sony tech and he told me that any machine locked to video sync is really running at 47.592kHz SR, not true 48kHz.

Depends on what kind of machine...and how it's set up...

Most modern video machines, such as Digibeta, D5, and HD Cam running NTSC actually do record digital audio at 48k (unless they are doing sample rate conversion internally, which I have not heard of). Pro Tools and other DAW's can usually be set to either record actual 48k or 47.952k when locked to video sync. Production DAT's for film are usually recorded 48k, 30 fps. When locked to video sync, these DAT's would run at 47.952 (or 48k pull-down) to match the film to video transfer. If a production is being shot on film, but will be posted on NTSC video, then it would be desireable to shoot production DAT's at 48.048, so that they will be pulled down to 48k when locked to video to match the film transfer.

Bottom line, make sure you know how the editorial department is working before loading in a lot of production DAT's. If in doubt, go analog.

rcm

[CCash]

I'm seeing a lot of projects that need to run at 29.97/48k no pulldown (OMFs). It always makes me leary, but I have to trust the pic department on this. If the production was shot to film, and audio was recorded on DAT at 30fps/48k, then the picture dept. had to, at some point, sample rate convert .1% to match the telecine'd picture and still be at 48k.

When I lay back, they tell me to just keep it at 48. A lot of these laybacks are on DA-88 and go straight to Dolby for 5.1 printamstering. CLEARLY label the tapes as 48/29.97! Dolby and whoever does the film print will know what to do. Someone has to pull it up at some point for film. I don't mind doing it, but as I said, my delivery specs are 48/29.97.

[potatohead]

It sounds like your film and HD picture departments are utlitizing a relatively new project spec in recent Avids called '23.976p'.

Here's the skinny about these two kinds of Avid projects (available with the most recent versions of Film Composer and Xpress Pro):

1. a '24p project' implies audio will play back at 47952Hz (or 44056Hz) in sync with NTSC video.
2. a '23.976p project' implies audio will play back at 48000Hz (44100Hz) in sync with NTSC video.

That's it. Both 24p and 23.976p projects allow filmframe-accurate 35mm negative cutlists for film finishing. But the new 23.976p project spec allows for true 48000 with NTSC videoref picture. This new project type accomodates digitizing audio digitally from digital video sources (Digibeta, DVCAM, etc.) which can ONLY operate at 48000/NTSC. To get a true digital audio path from production through telecine to picture editorial to sound post, you would need to:

1. the original production sound MUST be recorded at 48048. (2channel 16bit ideally)
2. In telecine, this audio will be pulled DOWN (not samplerate converted) while being digitally copied to DVCAM or Digibeta in sync with NTSC picture of pulled-down film pix. (16bit 2 channel)
3. In the Avid,the project will be setup to be a '23.976p project' before beginning digitizing.
4. DVCAM or Digibeta can be digitized with audio digitally via AES/EBU. This audio is 48000.
5. down the road, OMFs will be turned over to you in sound post.
6. Your protools sessions will be true 48000/29.97. voila!

This scenario was NOT possible before the creation of the new 23.976p format. This was primarily designed to accomodate HD projects, since as far as I understand it, all HD video formats can only operate at true 48000 with 23.976 or 29.97 pix.

Can anyone else confirm?

I hope this explanation wasn't too muddled,
-Phil Benson

[CCash]

Cool, that may explain why I keep hearing the picture guys talking about HD masters. I'd just ask them, but they're paying by the hour, and they get squirmy when I start talking about things like pulldowns.

So they can do this 23.976p video xfer from picture that originated on film? I have my doubts though that all of this production audio is recorded at 48048. I suspect they are sample rate converting pulled down audio (47942) to 48k, which may help explain why some of these OMFs sound tampered-with (aliasing for example).

With the 23.976p, wouldn't they need to pull-up to go back to film? Alright... my head's starting to hurt. Hope we didn't hi-jack this thread.

[minister]

1. the original production sound MUST be recorded at 48048. (2channel 16bit ideally)
2. In telecine, this audio will be pulled DOWN (not samplerate converted) while being digitally copied to DVCAM or Digibeta in sync with NTSC picture of pulled-down film pix. (16bit 2 channel)
3. In the Avid,the project will be setup to be a '23.976p project' before beginning digitizing.
4. DVCAM or Digibeta can be digitized with audio digitally via AES/EBU. This audio is 48000.
5. down the road, OMFs will be turned over to you in sound post.
6. Your protools sessions will be true 48000/29.97. voila!

This scenario was NOT possible before the creation of the new 23.976p format. This was primarily designed to accomodate HD projects, since as far as I understand it, all HD video formats can only operate at true 48000 with 23.976 or 29.97 pix.

Can anyone else confirm?

confirm? well, i can attest that the last two HD projects i did were EXACTLY like this. video finish. no pull on my end or for layback. one layback was to Digibeta, one ended up an MPEG stream on an HD server/player in the theater. no drift or sync issues. i was told by the video editor that this how the 23.976p work flow is.

[minister]

i do realize that you guys were talking about creating mixes for films that will be printmastered and on 24FPS prjection. but, for HD playback, that is the scenario. my delivery was 48/29.97 (and AC3)

and my program was cut in FCP4 HD. Sony format. (though shot Panasonic)

as for location audio, i'll ask on the film i worked on to see if anyone knows. i doubt it as well. not that location guys are dumb. but are they informed? maybe. or maybe some are and some are not.

as for the pull/up down for 23.976p, i'll ask because there would be some kind of insert pull up/down to create the 29.97HD and SD versions. or, would they just interlace and do a fancy "3:2 pulldown" or whatever the numbers are for 23.976 to 29.97.

[JKD99]

Hi
Check the sound reports, they should have the frame rate and sample rate info on them, and the picture department probably has copies if the originals are vaulted or something.

good luck!