23.976 frame rate explained

Question

This post was triggered from this this thread:
http://discussions.apple.com/thread.jspa?messageID=4741388#4741388
I just thought it best to start a new one
Okay iSchwartz, with the speed of a flying bullet, and with help from my fellow members of the IBS (Institute of Broadcast Sound - in the UK), I think I have some answers...
24P is indeed simply video at 24frames per second with the "P" meaning Progressive scan. Its a video format invented to be compatible with film. It also means that the footage will have more of a "film look" when its converted to TV frame rates for broadcast as it will have the same process applied to it as film footage.
As to where 23.976 fps comes in (with regards to Logic) is rather more vague!
(warning - the following contains some speculation!)
As all will know because film is shot at 24fps it needs a special conversion process to be shown on an NTSC TV of 29.97fps. The process could just speed the film up but it would look funny and so they sort of duplicate some of the film's frames instead, to get the frame rate increased. The process used would result in a frame rate of 30fps so to bring it in line with the (cumbersome) NTSC frame rate they have to slow the film down slightly (by 0.1%) before they "scan" in the film's frames to make video.
...and guess what a 0.1% speed reduction of 24fps results in? Yes - 23.976!
so...
23.976 is the frame rate of the telecine machine when playing film to transfer to NTSC tv. The process involves slowing the 24fps film by 0.1% to 23.976 and applying a 2:3 pulldown picture process, resulting in NTSC's frame rate of 29.97fps
Now the question is why would you want Logic to work in 23.976fps?
It is possible (I don't know for sure) that when you shoot with film (ie 24fps), destined for tv that the programme is edited at 23.976, ready for the telecine process, and so this is the frame rate used during the post production process - As it is the time reference used in the edit then we need logic to work at this rate too so we're all in time.
It is also possible that the latest HD video cameras provide a shooting frame rate of 23.976 fps so that the "slow down" process of the past is not required.
Having said that to view the 23.976 fps pictures on telly the video needs to be converted to 30fpsDrop - or you need a display that can work at this unusual frame rate. I am not sure what the implication of all this would be for the musician "working to picture".
One thing I would say, is that musicians are not alone in having much confusion with frame rates and time code, especially now Hi def has arrived. I would strongly advise double checking with "production", particularly the dubbing editor, if that frame rate requested ~really~ is the right one!
I hope I haven't confused the issue even more with all that! Don't take any of this as gospel as I am still learning too. I trust someone will provide corrections and additions.

Answer 1

Rohan,
I agree in so far as the musician should not have to worry about the technical aspects of picture, but the composer is working within a team of people who have to be able to communicate effectively. the composer is also part of the production's overall workflow and so the composer's work methods can be dependent on productions.
To answer you points individually...
- when the telecine is created, and then sent for offline editing, it is the offline edit that you receive with the BITC or the striped LTC (rare these days) that should be your guide. obviously in the states with the confusing NTSC format, it is important to be sure what format they have used in the offline process, but ultimately it is the production facility to ensure you have a video edit that you can work to
Your first sentence says it all. If the offline edit is in 23.976 then presumably this is what you'll get sent. I have no idea how this will get delivered as the format would not work on video tape, you wouldn't be able to view it on a standard TV either. You could view it as a quicktime movie. That is the only way I can think of.
I agree it should be up to production to provide you with what you can work with but how far must they accommodate? I doubt anyone would be too happy providing U-matic tapes these days. For my last job I wanted QT movies on a DVD-R but I had to settle for DV tapes and capture myself. Lets face it, as technology gets cheaper and more accessible we are increasingly expected to be able to handle all those advances!
- so the music you create can either sync to a master clock (which is rare other than word clock which is not for video syncing anyway) or simply to the QT or VHS that you have been provided with which should have standard frame rates. you simply compose your music based on that sync
I don't know what you mean by "master clock" in this context, and as you point out word clock has no timing information at all and is irrelevant in a timecode discussion. Yes you work to the movie you've been given, but what if its using 23.976fps? If it is, it wont be on VHS - and, you wont be able to sync properly to it in Logic as Logic doesn't work with 23.976
If production provides you with a "special copy" in say standard NTSC 29.97fps then the editors timecode will be different to yours. You wont be able to talk timecodes with them over the phone for example. For them to do this production will have to convert the footage specially for you using 3:2pulldown telecine process (so the film plays at the right speed) and I'm not sure they would pay for that!
- the issue is more critical in the dubb, but generally 1 second of music at whatever frame rate is still 1 second of music. when you send your music in it is almost never smpte locked unless you have delivered via a timecoded DAT something which is very rare these days. basically it simply measures the sample rate and then syncs within the DAW in the dub
1 second in NTSC's 29.97fps is 1second at 23.976fps which is 1 second in PAL's 25fps too;-) Its the number of frames within one second that has changed. The problem is the format of the movie. you can play it in QT but not on the telly and Logic doesn't have a time base to match with it. It is likely that logic will be able to follow the movie in QT (not sure of that), or "chase" it, but Logic's own smpte display will not match the movie's BITC. Indeed all of logic's time references will not match the movie's.
when you send your music in it is almost never smpte locked unless you have delivered via a timecoded DAT something which is very rare these days. basically it simply measures the sample rate and then syncs within the DAW in the dub
Ever heard of BWF? Bounce your finished music in logic as a WAV file and you actually get a timecode stamped "Broadcast WAV" file: a file that has the SMPTE time of where the music starts in the film. The timing info is embedded in the file. All the dub mixer has to do is press a key-command to place this file in the right place in the film. I worked this way on my last project. (Its also how logic can place any audio file into "its original recording position")
Without using timecode I'm wondering how you tell "the dub" where the music should go in the film? - I'm genuinely curious. In the past when delivering music without timecode I would still say, in a written note for eg, the track starts at some timecode point (as referenced to the BITC for eg). This is why the composers timecode needs to be the same as the dub/editor's!
- it is simply important for the people sending you their film to agree how many frames consitute their second. if you have a VHS playout from the offline, you should work to whatever format that VHS or DVD comes in; NTSC or PAL. it's not your job to worry about the film to offline telecine
A nice thought in theory:-)
It shouldn't be our job to worry about such things (bars, beats, keys and harmony are enough for me!) but we may not have the choice if we want the job!
Don't get me wrong here Rohan. I don't profess to understanding all this stuff properly and I have never been asked to work in 23.976fps. I went down this line of enquiry to see if I needed to know about it! Perhaps you are right and production will supply a special version for the composer - but I'd like to know if this is the case as I like to have a basic grasp of the overall production process. I'd love to know of anyone who has had to work in this frame rate and how typical it is becoming (if at all).