SMPTE question about 29.97 fps

[MJGreene Audio]

I was going to explain this but decided to copy/paste this from the net. Its been to many years since I actually thought about the difference so here you go: Good luck.


In order to accomodate the extra information needed for colour the black and white 30 frame/second rate was slowed to 29.97 f/s for colour.

Although usually not an issue for non-broadcast applications, in broadcast, the small difference between real time (or the wall clock) and the time registered on the video can be problematic. Over a period of 1 hour (SMPTE) the video will be 3.6 seconds or 108 extra frames longer in relation to the wall clock. To overcome this discrepancy drop frame is used.

Drop frame: Every frame :00 & :01 are dropped except for minutes with 0's (00:, 10:, 20:, 30:, 40: & 50

The gist of it is yes, Two different formats.

[mlocascio]

Originally Posted by MJGreene Audio

I was going to explain this but decided to copy/paste this from the net. Its been to many years since I actually thought about the difference so here you go: Good luck.


In order to accomodate the extra information needed for colour the black and white 30 frame/second rate was slowed to 29.97 f/s for colour.

Although usually not an issue for non-broadcast applications, in broadcast, the small difference between real time (or the wall clock) and the time registered on the video can be problematic. Over a period of 1 hour (SMPTE) the video will be 3.6 seconds or 108 extra frames longer in relation to the wall clock. To overcome this discrepancy drop frame is used.

Drop frame: Every frame :00 & :01 are dropped except for minutes with 0's (00:, 10:, 20:, 30:, 40: & 50

The gist of it is yes, Two different formats.

Thanks for the response.

I have heard some people say that 30fps DF is the same as 29.97, and others say it is different. OK, I understand they may be two different formats, but can one achieve rock solid sync by having the master feeding 29.97 and the receiver set to 30fps Drop Frame???

[opentune]

Well, MJ explained it already.

So 30 fps DF = 30 dfsp.

29.97 fps and 29.97 dfps coexist. The latter is for work with color video.

[opentune]

Originally Posted by mlocascio

... can one achieve rock solid sync by having the master feeding 29.97 and the receiver set to 30fps Drop Frame???

Ooops, didn´t see your second post. You were a little faster than me...

Uhhmm, i would say no. I don´t think it´s possible to get a rock solid sync with two different SMPTE settings.

[dkatz42]

This whole thing wildly confused me for awhile, and most explanations are lacking.

What made it work for me is the following:

Think of timecode as a numbering system for frames. The rate at which the numbers flip is the same as the frame rate (30 Hz or 29.97 Hz.)

If you want the timecode to match the wall clock time (more or less) and you're running at 29.97 fps, the frame numbering has to occasionally skip numbers in order to stay in sync (it actually varies back and forth a bit relative to the wall clock.)

"Drop Frame" is really a misnomer; what's being dropped are Frame Numbers.

So there are two parameters--the frame rate (29.97/30) and whether or not frame numbers are being dropped.

[MJGreene Audio]

If you have the option to stripe code at the same "Flavor" as the original tape or "Master" you will save yourself a head full of grief. The later syncronizer's like the Lynx systems do wonders especially compared to the earlier days. But it is always good to stripe the same code. If your not sure then find a Brainstorm Dystripilizer (SIC) and it will tell you what your code is. We used to get video dubs from post houses that said one thing and the code wasn't even close.

Makes me grateful for quicktime DV movies and Pro-Tools....

Michael Greene

[Mazaga]

Let's simplify it:

Black & White TV = 30 fps

Color TV (NTSC) = 29.97 fps (this can be DF or NDF)

EBU = 25 fps

film = 24 fps.

As you see there is only four frame rates to consider and drop or non-drop are variants of the 29.97

video people refers to 29.97DF saying 30DF
and 29.97 NDF as 30 NDF

Theoretically speaking 30 df doesn't exist.

M.

[mlocascio]

Let me re-phrase the question...

I am currently syncing my analog 2" machine to a Digi 002R and getting rock solid sync with the following set-up:

Black burst generator
Timeline Lynx 1
MOTU Digital Time Piece
Lavry Blue A/D - D/A

The MOTU DTP takes the black burst signal and sends out word clock to the Lavry's which in turn sends the clock reference to the Digi 002R via S/PDIF. The DTP also reads the SMPTE LTC coming from the analog 2" machine and converts it to MTC and sends it to the 002R via it's MIDI input.

The problem is that the Lavry’s don’t have a video in for black burst, and the fidelity of the converters is degraded considerably when clocked to the DTP. I recently tested the Lavry’s clocked to a Big Ben, which accepts black burst, and the situation is much improved.

I want to replace the MOTU DTP. I plan on purchasing the Big Ben to handle the black burst clock reference, and I am considering a Rosendahl MIF3 for converting LTC to MTC. The Rosendahl front panel only shows SMPTE frame rates of 24, 25 and 30, and drop frame. Because the black burst generator is used for house sync, the SMPTE frame rate is 29.97.

One of my techs said that 29.97 is the same as 30 fps except that the clock reference is slightly slower at 29.97. Therefore he said the Rosendahl should work fine at 30 fps because the Big Ben would lock to the black burst signal and send the slower clock reference. Makes sense to me, but I’m no expert.

Can anyone confirm or deny this?

[dkatz42]

Originally Posted by Mazaga

Let's simplify it:

Black & White TV = 30 fps

Color TV (NTSC) = 29.97 fps (this can be DF or NDF)

EBU = 25 fps

film = 24 fps.

As you see there is only four frame rates to consider and drop or non-drop are variants of the 29.97.

Don't forget 23.976 (Film-emulating HD, so that it doesn't take weeks of computer time to transcode to SD at 29.97.) No DF at this rate, unfortunately (and a lot of bugs in the tools.)

[minister]

Originally Posted by mlocascio

One of my techs said that 29.97 is the same as 30 fps except that the clock reference is slightly slower at 29.97.

your tech uses sloppy language. they are not the same. (they are close in speed) you should have one master clock. black burst is 29.97.

drop frame is a method for broadcasters to have nice round numbers on the minutes and hours so that they can program more easily. 30 DROP frame is a non sequitor.

29.97 ND and 29.97 DF are the exact same SPEED. but the positional naming scheme is slightly different. your measuring stick is slightly altered, but the running time, relative to an absoulte cloick is the same. 30 is .1% faster, and would therefore be shorter in length given the same frame count relative to 29.97. make sense?

Originally Posted by mlocascio

Therefore he said the Rosendahl should work fine at 30 fps because the Big Ben would lock to the black burst signal and send the slower clock reference. Makes sense to me, but I’m no expert.

this is not the way to set it up. it doesn't make sense to have a clock clocked to 30 and then pass 29.97 to the other devices. everyone needs to be at the same rate. pick ONE clock rate and pass that to every device in the chain. if you are simply doing music, and you are not locked to video, then chose 30FPS for every device and don't worry about BB.

[Mazaga]

Originally Posted by dkatz42

Don't forget 23.976 (Film-emulating HD, so that it doesn't take weeks of computer time to transcode to SD at 29.97.) No DF at this rate, unfortunately (and a lot of bugs in the tools.)

I have never heard about it...

thanks for the info

M.