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Working on a custom isolated music track, where official soundtrack tracks are placed in sync with movie audio; what's about blank parts? Should I replace them with the movie track (eventually with needed fade ins/outs)? Or with movie track without dialogs? Or should I leave them blank, silenced?
EDIT: and, why, out of curiosity, the CD soundtrack, once aligned, is perfectly in sync with a 23.976fps source? 
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The isolated movie tracks I have listened to tend to be everything bar dialogue, so sound effects too
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Individual tracks are probably short enough to not drift out of sync. 23.976fps is 99.9% the speed of 24fps.
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Agree. But in a minute (60s = 60000ms) a 0.1% difference (60ms) is way noticeable, and I'm talking about two or three minutes tracks... that's why it's strange!
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Perhaps the tracks were already slowed to 23.976fps for some reason.
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The isolated scores that I've come across have left parts not covered by the music blank. That's what I'd do.
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Was wondering the same about Armageddon. There is a method called "rear channel rip" (I hope that's the right term) based on the apparent fact that most movies have only soundtrack and some effects in the rear channels. I think that's what I'll use. Synced soundtrack for most of the movie and where I can't find a soundtrack or where there is no music, I'll use the rear channels inserted as stereo.
I would assume that the CD is synced to 24fps, as that is what cinemas use or used to use. It's probably just slowed down for the Blu Ray/DVD releases by a bit.
But since you'll be syncing individual tracks anyway, this will never become a serious problem. The drift for a 10 minute audio clip would only be 0.6 seconds. Most clips are much shorter.
Math: (24000/1001/24)*60*10 = 599.400599401
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(2018-04-14, 07:10 PM)zoidberg Wrote: Perhaps the tracks were already slowed to 23.976fps for some reason.
I guess so, but don't know why - shouldn't a soundtrack be in sync with film (24fps), or it's not mandatory?
(2018-04-14, 07:41 PM)TomArrow Wrote: But since you'll be syncing individual tracks anyway, this will never become a serious problem. The drift for a 10 minute audio clip would only be 0.6 seconds. Most clips are much shorter.
Math: (24000/1001/24)*60*10 = 599.400599401
This WOULD BE a serious problem! Human beings (with normal hearing capabilities) are capable to hear to 10/20ms drifts (in relation also to frequency), so two tracks (one 23.976fps, the other 24fps), would start to be noticeably out of sync after ten/twenty seconds!
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Sorry, I don't know why, but I started THREE threads with the same subject...  fixed now!
Dunno if to use front channels, rear channels, or using a six channel track and put the music only on the front channels...
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You'r eright. It would be a serious problem, if there is a lot of correlation between the image and audio. Speech is a good example, but even there we can tolerate a drift to a certain extent. Extremely rhytmic music cut to the video may also be a problem. But most movies have classical scores that do flow with the picture, but not fully "to the beat", if you know what I mean. Unless you had edited it yourself and knew exactly what to look for, it's improbable you would notice any issues.
Either way, you can just test it out.
There's also another aspect to this, which is analogue recording. Older stuff was recorded with analogue stuff, which inherently suffers from things like flutter etc. and never has 100% consistent playback speed. Not sure how much this would account for though. Probably depends on the amount of cash and calibration applied to the process.
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