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  #1  
Old 08-08-2008, 03:26 PM
subwoof subwoof is offline
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Default Imax specs, sample rate conversion?

I'm working on an Imax film at 48 Khz, 24 bit, 29.97. Imax requires deliverable sound at 16 bit, 44.1, 30 fps (film speed). I am assuming that the finished 6.0 mix tracks will need to be imported into a new PT session to convert them to that format, and pull up the sound. My question is should I make a new session at 30 fps, 16 bit 44.1 and import the tracks doing a SR conversion set at 47.952? Won't that make the tracks longer by .1% NTSE to Film? Does the new PT session need to be at 30fps, or can it still be at 29.97 fps? I don't intend to deliver the actual session to IMAX, just the .wav audio tracks.

Thanks for any replys

Mike
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Old 08-08-2008, 04:44 PM
JKD99 JKD99 is offline
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Hi Mike,
This is what I would do: A session running at 30 fps uses the same audio file setup as 29.97 with the 0.1% pulldown checked. Think of it as production dailies recorded at 30fps in a session that's dubbing to 29.97 video. You have to slow them down 0.1% to sync to the telecine'd video.

So,if you've been mixing at video speed (29.97 no pull) then do your SR conversion (and bit depth) using 48048 as your source. If you were going the OTHER way, film to video, pull to no-pull, you would use 47952 as the source. If you've been mixing at 29.97 w/ pulldown, then you're done already except for the SR conversion itself (no speed change necessary). Just change the TC setting in your sessions and line up the 2-pops. Or in your case, put the files on a DVD and ship'em.

Of course, please be sure of the post-production chain that applies to your project, obviously I have no way of knowing how the various steps have been accomplished leading you to this point.

Hope this helps,

Joe
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  #3  
Old 08-08-2008, 05:57 PM
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minister minister is offline
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Hi Michael,

Yes, IMAX is 16/44.1kHz/24fps. However, why do you think there is a speed change you need to do in order to get to 16/44.1? Was it shot 70mm with a traditional Telecine in order to give you a 29.97 picture? If so, then, yes, you need to change the speed. (I would verify that this was the process)

You don't need to create a 30fps session, the Frame Rate will not affect the speed, but the SR conversion will. Besides, your target is 24 fps. The field recorders and DAT's in the old days would not do 24, but would do 30, which is why you may be thinking 30.

By the way, NTSC to FILM speed is a Pull UP, so the resultant file is SHORTER.

As Joe suggests, create a session at 48k then import the mix files using SR and select that the SOURCE tracks as 48048. Your files will convert and go to "film speed". Then select and export them as 44.1kHz, THEN ship them.
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Old 08-09-2008, 02:31 PM
subwoof subwoof is offline
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Thanks Tom and Joe. Generally I don't do the Imax mixing at my facility, so I don't have to worry about these issues. I cut the tracks and let someone ELSE do the sample rate and speed stuff!

Thanks again,

Mike
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Old 08-09-2008, 06:00 PM
Phil Jeffers Phil Jeffers is offline
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Heya Mike, they use 6 track interleaved WAV that isn't supported by Pro Tools also (that is it cannot import or export). I've used Sound Forge to get around this (or Peak Pro on the Mac). They may do this for you though, not sure.

Are you Re-Recording Mixer on this one?

Cheers, Phil J.
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Old 08-09-2008, 07:31 PM
subwoof subwoof is offline
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Phil, yes I am sound designer and re-recording mixer on this one. Usually we mix at Skywalker, but not this time (budget!) Concerning the interleaved file, I was under the impression that if I export as a stereo interleaved format, it would indeed take all 6 tracks as one interleaved file. But I'm pretty sure they would also accept 6 mono tracks as well.



Mike
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