It’s a high-definition world these days. The vast majority of new content for TV is in HD, movies can now be gotten in HD on Blu-Ray, and you can even stream HD content online. Post production workflows have changed accordingly, and one of the areas of biggest confusion has been the move to 23.976 FPS timecode.
To make matters more complicated, it’s all too common for work picture to be delivered to post sound on a standard-definition format like Beta SP or DVCAM that still has to use 29.97 timecode. But your final mix is still expected to sync up to that HD master at 23.98! So you need to work in 29.97 and then convert to 23.98 for final layback. Do you need to conform anything? Will there by sync issues? Will things drift? What’s the deal?!
Fortunately, it turns out that things aren’t so bad. Both 23.98 and 29.97 travel at NTSC speed, which is 0.1% slower than real time. It’s a whole other topic to break that sucker down, so for now we’ll just stick with the fact that they both travel at the same speed. The only difference is that they divide up a second into a different number of frames. The bottom line is that things retain perfect sync when going between 23.98 and 29.97 FPS.
For Pro Tools this means that as long as your session start time is 00:00:00:00 then 23.98 and 29.97 will match up exactly at every whole second, including the hour. Here’s a snapshot of Pro Tools in 23.98 at 01:00:00:00 (click any image to bring up a full-sized version)
And now here’s a screenshot where all I’ve done is changed over to 29.97 in the Session Setup window without moving my insert point at all. Notice how we’re still exactly at 01:00:00:00 – also notice how my grid lines (which are set to 1 frame) are more frequent, because 29.97 divides a second into more frames than 23.98 does.
Now let’s go to a timecode in 23.98 where the frame value isn’t 00:
So we’re at 01:05:00:08 in 23.98, and here’s what happens when we change over to 29.97 without moving our insert point at all:
Ah ha! The frame value changes! But has anything moved around? Is our sync all messed up now? Nope, everything is fine.
Pro Tools only has one time ruler that is absolute and completely precise, and that’s the “samples” ruler. You can’t break digital audio down into segments any smaller than a single sample. So this means that every region on your timeline has an absolute sample position that doesn’t change regardless of the timecode setting. Demonstrating this proves that sync doesn’t change when moving between 23.98 and 29.97:
Here’s a region of pink noise spotted in 23.98 timecode – notice the sample position in the sub-counter is 207887680:
Now change over to 29.97. Will the region move? Or will it retain perfect sync on the timeline? Take a look at the subcounter below:
Our frame value has changed, but the sample valus is still exactly 07887680. Sync has been perfectly maintained even though we’ve changed from 23.98 to 29.97.
So the good news for audio post is that there’s really nothing you have to worry about when editing or mixing in 29.97 and then outputting to 23.98. Unless you’re working in drop frame… but that’s another story!
This stuff has always been tricky for me. Perhaps you can answer this question:
Im posting a low budget independent film that was shot at 23.976, so obviously my frame rate in PT is set to 23.976 as well.
Now, this film is going onto dvd, so I’m assuming the video will have to be converted to 29.97 for this. Will I have to change the ‘speed’ of the audio stem in order to maintain sync with the video that has been converted from 23.976 to 29.97 fps?
Hi Nick,
thanks for posting this question! This is of course the heart of the matter, and you’re in very familiar territory for lots of audio post folks. Everything goes to DVD eventually it seems, but of course more and more content is acquired at 23.98 these days.
The good news for you is that there is absolutely no speed difference whatsoever! Everything will stay in perfect sync (as long as it started that way, of course!
)
Just be sure to spot your audio using a whole-second value like 00:58:30:00 or 01:00:00:00 and it will match perfectly when transitioning from 23.98 to 29.97. There will be no drift or speed issues of any kind.
I hope that helps!
I think if you make a clear separation between “speed” (ie. film speed) which is a function of sync measured in pulses from a sync generator, and “timecode” which is just a frame marker and has nothing to do with speed, the lesson will be clearer. To put it briefly, 24 and 30 frames = film speed. 29 and 23.97 = video speed. The only change that needs to take place is between film speed and video speed. Maybe even a little history would help. Otherwise, well done.
I’m wondering if this applies to a confusion I’m having and if you might be able to help. I have a film in final cut at 23.98 that i need to deliver quicktimes of the reels to an audio post facility with a timecode burn in. their specs say “frame rate must be 29.97 non drop.” i tried exporting the quicktime then using compressor to convert it to 29.97 and add timecode but everything was a frame off from the original quicktime i exported from final cut. another editor i spoke to who has worked with this audio facility said that i actually don’t have to convert the video as long as my timecode is 29.97 non drop. the facility is using pro-tools and they said that if i didn’t convert the video to 29.97 and just did the timecode 29.97 non drop that sync would be a problem. sorry but i’m really confused, if you can help in any way it’d be greatly appreciated.