30fps to 24fps?

[Cracker Funk]

Originally Posted by AudioPostExpert

Ah but it does matter because in audio post we have to deal with all the production sound. So frame rate changes between filming and editing (before audio post) could cause exactly the same problem that we've experienced between editing and audio post. In audio post (whether done by a dedicated audio post guy or the picture editor), you frequently have to go back to the original production sound to find replacement/alternate dialogue, which is going to be a serious problem if the speed of the picture has changed in anyway since the filming because the original production sound will no longer sync with the picture.

The only way this could effect audio post would be if the audio was recorded with a time stamp. And if you don't notice that your audio time stamp is 20% off from your edited video, you've got bigger problems. All you would have to do is ignore the time stamp. Audio has no frame rate.

Originally Posted by AudioPostExpert

With the tried and tested workflow of changing frame rates between filming on 35mm film and editing on video, the speed differences were known and predictable and the production sound mixer would use a pull up sample rate so the production sound could be pulled back down during audio post to sync with the picture edit.

Thank God we don't have to do that anymore. We can now just use the original audio, unmodified. How awesome is that? Hooray for the digital revolution!

Originally Posted by AudioPostExpert

As we have discovered though, when using interpolation in Premiere to convert between frame rates, there are slight discrepancies in picture speed/frame positions, nothing visibly noticeable but enough to cause sync issues with the sound in places. The problem is, that these discrepancies are no longer known or predictable and so cannot be compensated for as could be done with the standard workflow which involved frame rate changes.

When did we discover that? I see absolutely no reason why interpolation should even enter this conversation, neither for video nor audio.

Originally Posted by AudioPostExpert

Relating this all to the OP's question, he could have problems during dialogue editing when he goes back to the original production sound recorded when the picture was at 30fps.

He could? Why? The recording format of the audio is constant. You can put it in any timeline, and nothing changes.

Originally Posted by AudioPostExpert

One last point, Premiere is obviously interpolating both the picture and the linked audio (to maintain sync). Even expensive professional audio tools have difficulty with this type of process without causing some artefacts. You may not notice these artefacts under some conditions but in a cinema, say at a film festival, it's far more likely. It's certainly something I would be concerned about in a professional project.

Oh, it's obvious? I see no evidence of such (nor any logical explanation as to why this would be the case). Interpolation happens for pulldowns, and that's not what we're doing.

[AudioPostExpert]

Originally Posted by Cracker Funk

The only way this could effect audio post would be if the audio was recorded with a time stamp. And if you don't notice that your audio time stamp is 20% off from your edited video, you've got bigger problems. All you would have to do is ignore the time stamp. Audio has no frame rate....

The recording format of the audio is constant. You can put it in any timeline, and nothing changes.

Yes, the production sound is constant but the picture isn't. If the picture and linked sound slows down by 20% the original production sound (not the audio in the timeline) will be 20% out of sync with the new picture. So we can't (easily) go back to the original production sound looking for alternative takes or mics to replace problem dialogue. This more serious problem is in addition to any problems caused time-code related issues.

Obviously when using Premiere we're not slowing the picture down by 20% because we are interpolating but:

Originally Posted by Cracker Funk

"[when using interpolation in Premiere to convert between frame rates, there are slight discrepancies in picture speed/frame positions, nothing visibly noticeable but enough to cause sync issues with the sound in places.]": When did we discover that? I see absolutely no reason why interpolation should even enter this conversation, neither for video nor audio.

From post #24: "BTW, in the two different frame rate versions you sent me, I extracted the embedded audio from both and compared them with each other and the separate audio scratch track supplied, most of the time the sync was reasonably close although not perfect but in other places there was up to 4 frames difference between them. This is significant and why changing picture frame rates can be problematic."

G

[Cracker Funk]

Originally Posted by AudioPostExpert

Yes, the production sound is constant but the picture isn't. If the picture and linked sound slows down by 20% the original production sound (not the audio in the timeline) will be 20% out of sync with the new picture. So we can't (easily) go back to the original production sound looking for alternative takes or mics to replace problem dialogue. This more serious problem is in addition to any problems caused time-code related issues.

Obviously when using Premiere we're not slowing the picture down by 20% because we are interpolating but:

When you put 30p footage into a 24p timeline, you are neither slowing the footage down, nor interpolating. Every fifth frame is ignored.

Originally Posted by AudioPostExpert

From post #24: "BTW, in the two different frame rate versions you sent me, I extracted the embedded audio from both and compared them with each other and the separate audio scratch track supplied, most of the time the sync was reasonably close although not perfect but in other places there was up to 4 frames difference between them. This is significant and why changing picture frame rates can be problematic."

And I already tried explaining to you how this has nothing to do with the concerns of the OP. The headaches caused by exporting a 23.976 project to true 24p is an entirely different conversation than the one we're trying to have to help the OP, who is concerned about using 30p footage in a 24p timeline. These two subjects are not related. At all. Nil. You're confused, and are confusing the conversation.

There's nothing more I can say about this; I'm done with this conversation.

[AudioPostExpert]

Originally Posted by Cracker Funk

You're confused, and are confusing the conversation.

I agree, I'm not an editor, I do find it confusing and I am confusing the conversation. But, I believe I am doing this with good reason. To start with you're assuming the OP is really talking about 23.976fps and 29.97fps. Even if this assumption is correct, in my experience, professional editors tend avoid just dropping every 6th frame due to motion stutter or artefacts from frame blending. I've heard of all sorts of weird and wonderful ways to get from 29.97 to 23.976 using Cinema Tools, Shake, After Effects and Optical Flow. As I said though, I am confused, I don't know or understand all the ins and outs of all the different pull-down, interpolation or other processes which can be used for this particular conversion. However, what I do know for sure is that they frequently cause problems during dialogue editing when it comes time to refer back to the original production sound.

I had assumed that Premiere was using some other, more convoluted processing than just dropping every 6th frame but in the past, all the picture/video editors I've worked with used FCP or AVID, so I've no experience of Premiere or of working with an editor using Premiere. So, I was assuming it was interpolating or doing some other process which would affect the audio because we've already discovered that it's not very accurate when it comes to audio sync with it's interpolation algorithms.

Baring in mind though that the OP is using FCP7 and not Premiere, I think my comments in general and my statement that the OP *could* have sync issues with the original production sound were appropriate. Hopefully, whatever method the OP chooses to convert from 30fps to 24fps, he will check that sync with the original production sound has been maintained before he gets to the stage where it causes a major issue.

G