THE definitive explanation of 29.97 and 23.98 timecode

[huub]

Okay..
I was confused this weekend, because a job was changed last moment to 24p (well 24isf to be exact)
And I was not completely sure if I should record the multitracks at 48khz..
I suppose different samplerates are only used if a producer/audio post person specifically asks for it?

thank again,
huub

[minister]

Originally Posted by charles maynes

it is not uncommon for audio to be shot at a pulled down digital rate of 47.752..... especially for commercials....

48048 is more common as it is pulled down when played at 48000.

[charles maynes]

I would defer to Tom's comments, but I have seen pulled down rates used as well- usually if film is going to intercut with video. If this is an HD project I would expect the SR to be 48 or 96 though.

[jayfrigo]

Originally Posted by starcrash13

Going from 23.976 to NTSC requires a 3:2 pulldown which is not a speed change, but rather an addition of repeated video fields to go from 24 frames to 60 interlaced video fields.

Sorry to be so nit-picky but, after all, this is "THE definitive explanation of 29.97 and 23.98" frame rates, right?

While you're being picky, it may be worth noting that 3:2 is no longer used; currently a 2:3 pulldown is used, i.e. AA BBB CC DDD, not AAA BB CCC DD.

[starcrash13]

Originally Posted by jayfrigo

While you're being picky, it may be worth noting that 3:2 is no longer used; currently a 2:3 pulldown is used, i.e. AA BBB CC DDD, not AAA BB CCC DD.

Right. Most people still call it 3:2, though. It's one of those "cool" industry terms where you say one thing, but maybe mean another like 24p, pullup, or conform.

[Bob Olhsson]

The problem is getting sound and picture editing gear to work together.

I once had a fascinating conversation with an old Ampex engineer. It seems the whole thing was never really necessary. What happened was that NTSC color was rolled out running on a 60 Hz. clock exactly like B&W. At the last minute some people at Ampex who were researching video recording technology noticed bars running through the B&W picture of a color transmission. The FCC went into a panic and quickly figured out that pulling the crystals down .1% got rid of the problem. A few weeks later it was discovered only to be a problem with crystal-controlled lab monitors and not ordinary TV sets.

But it was too late...

[jayfrigo]

Originally Posted by starcrash13

Right. Most people still call it 3:2, though. It's one of those "cool" industry terms where you say one thing, but maybe mean another like 24p, pullup, or conform.

Lots of things like that. Plenty of people still call anything film to video telecine, regardless of whether its film scanning or actual telecine. Heck, I still sometimes say "to tape" (as in "print FX to tape") for anything that records, and I'm certainly not alone. But in a "definitive" thread, I try to be accurate... well, I try...

[hociman]

Originally Posted by Bob Olhsson

I once had a fascinating conversation with an old Ampex engineer. It seems the whole thing was never really necessary. What happened was that NTSC color was rolled out running on a 60 Hz. clock exactly like B&W. At the last minute some people at Ampex who were researching video recording technology noticed bars running through the B&W picture of a color transmission. The FCC went into a panic and quickly figured out that pulling the crystals down .1% got rid of the problem. A few weeks later it was discovered only to be a problem with crystal-controlled lab monitors and not ordinary TV sets.

But it was too late...

I am not going to say that the Ampex engineer lied to you, but I read a conflicting account of this. If you go to my website and read the Timecode PDF, you will find this.

The argument when color was developed was that the frequency of
the color subcarrier would create beating with the sound subcarrier that
would be visible on some black and white television sets. The sound
carrier, however, is frequency modulated. Therefore, beating would have
only occurred at a specific frequency. A GE engineer determined that if
the frame rate was dropped by .1% (from 30 to 29.97), that the beating
would be reduced, and compatibility would be maintained (Lehrman 220).
As a result of this change, 60Hz AC cannot leak into a video signal, or “bars
appear to roll through the picture every 17 seconds” (Schubin 29).

Again, I'm not saying the Ampex engineer doesn't know what he's talking about, but that's how I understood the issue. If this is going to be a sticky, perhaps we should work on figuring out if the truth is somewhere in-between or more towards one or the other.

[Bob Olhsson]

Perhaps the "some B&W sets" were in the Ampex Research lab and the guy at GE is who igured out how to fix the problem.

By far the very best explanation of pull-down I've ever read was posted by John Klett during in the late '90s. Maybe somebody else remembers where.

[klett]

Originally Posted by Bob Olhsson

By far the very best explanation of pull-down I've ever read was posted by John Klett during in the late '90s. Maybe somebody else remembers where.

Hey Bob

I remember writing it but I don't have a copy... it was pretty comprehensive and would probably be pretty useful if only someone could dig it up and paste a copy here. It would take me hours to recompose, which means it's likely I won't any time soon.

I posted the article you are remembering on PAN pre the interweb (as we know it today)... like - when it was on a dialup X.25 network running through Delphi maybe? so... 1993 or so?

The PAN Network still exists at The PAN Network Home Page

Anyone still have access to the PAN archives? I was supposedly given a lifetime membership but I lost track of my user and pass a long time ago and never felt the need to contact the PAN dude (Perry Leopold?) about it.

If one of use guys have access to that archive you can search posts from me that mention terms like "gearbox", video field and frame rates and standards for B&W vs Color etc. I went in to how digital audio was stored on video tape in the various formats and standards and how you had to turn the color correction off to make the transitions from on to off more reliable... and because you recorded digital audio for CD's on U-Matic in B&W the standard for video field rate for B&W would be 0.1% faster than for Color NTSC here in the states... anyone clocking their 1630/U-Matic combo at 59.94 is playing everything 0.1% slow... stuff like that - but more lengthy and detailed as I had more time back then.


klett