Remember this is an overview and not ALL the technical issues are addressed here. This is from a lecture I give to indie film makers....
Transfer in Post
Jumping ahead for a moment
resolving process: you must be careful to select the correct master sync frequency! If you shoot film at 24fps and have it transferred to video, the film will actually be transferred at 23.976 fps. Therefore, to maintain the correct sync relationship, the field audio must be transferred against a master clock frequency of 59.94hz.
This is easily accomplished with a resolver by simply connecting a video reference to the external sync input. The resolver will substitute the external video reference at 59.94hz for the internal reference of 60hz.
The field audio will now be resolved to video at the same rate as the film to video transfer.
Video Transfer in Post
It will not matter to the sync sound recorder whether you shoot at 24 or 30fps for video transfer.
The crystal oscillator will remain at 60hz either way.
If you are shooting at 30fps and will have your film transferred to video on a scanner it will be transferred at 29.97fps.
Therefore, to maintain the correct sync relationship, the field audio must be transferred against a master clock frequency of 59.94hz.
Again This is easily accomplished with a resolver by simply connecting a video reference to the external sync input.
The resolver will substitute the external video reference at 59.94hz for the internal reference of 60hz. The field audio will now be resolved to video at the same rate as the film is being transferred to video.
Recording sync Sound with Time code for film
• Camera rolls at 24 Fr/sec
• Sound Time code is 30 Fr/sec Non Drop
• DAT sample rate is 48K
• Exception: some long form TV shows use 30Fr/sec drop frame
• Have all involved communicate: Editor –Post production supervisor (or whoever is technically competent) should send written specs to camera crew, sound department, transfer (telecine) house, picture editors, post sound editors, final mix stage.
• Slate must show camera (Fps) and sound TC speeds. Label and all reports items Producers: Have everybody communicate
• It’s in the details
• Stick to the plan
Labels for Tape
• sound-boxes should include:
Camera frame rate
Sound TC speed Drop or ND
Sample rate if DAT
(-20 digital = 0VU )(1khz tone @ -20 = 1.43 v)
Production Title, Production company name with phone number
Date, Roll #, "DO NOT SUM" or "SPLIT TRACKS" or "SUM TRACKS" or "MONO" Optional: TC start and TC end (helps post staff when lost in a mass of material) -- (Maxell 124 labels are big enough for all that on a DAT!)
Playback labels: music reel box should be labeled too; the on set playback operator and telecine want to know:
Source of Time code [48Tr, DA-88, 2Tr
Studio Master, DAW…]
Original TC speed [29.97 typically]
Original sample rate [47.952K]
Play at 48K Suggested speed and/or sample rate changes on PB while playing back for filming (or taping).
Producers Stay Awake
Producers and Time Code ( why they need each other )
It’s only the producer’s money that will be wasted if no one pays attention to time code from production through post. Even though it’s feasible to keep high quality audio from production through editing to release intact, it is not likely. Someone will inevitably screw up, and that will cost money. Watch this process like a hawk and stay on top of it.
Picture editors usually can’t be bothered with location TC nor post sound. You, the producer, have to make sure that location time code from the flexfile from the telecine is loaded into the Editing Station. This has to be compiled with the picture cut list EDL and given to post sound editors. If you don’t pay attention through these steps, you will pay for it in time and money later.
Make sure that your audio is recorded well in production, give audio focus during a shoot. It will save you money later.
• Location TC has to get to the Avid intact.
• While assistant editors digitize the picture, they have to note the in/out location TC numbers for all takes.
• a sound editor has to use parts of non-selected takes for “fixes.” If they are smart assistants, they take care to note sound rolls as well as camera rolls.
• Really smart assistants scan the paper sound reports into graphic files on the computer and they won’t get lost as easily and accompany the project throughout.
Producers have to stay on top of the 30 and 29.97 issue. Also producers have to stay on top of the Drop and Non-Drop frame issue. If mistakes are made there is always a way to resolve it, but this will just cost more money.
The later the corrections are made in the production process, the more it costs. Time code makes good sound cheap, fast and easy. All decisions have to be made ahead of time.
ASSUME NOTHING and pay attention to your surroundings!
How to keep sound and picture in sync
• 24 frame/sec film shoot
o Shoot film at 24 Fr/Sec
o Roll sound with 30 Fr/Sec (non-drop, or drop) Time code and 48K sample rate
o Pre-roll only sound for 10 sec or more.
o Have the time code slate show numbers for 2 sec. to camera
o Slate appropriately
TOD (Time of Day) vs. REC-RUN Time Code
Time of Day Time Code
If the sound recordist records time of day TC (TOD), he/she should refresh the sync on the slate by jamming it at least every 4 hours.
Record Run Time Code
If the sound recordist uses RECORD-RUN TC there is never a problem with too short a pre-roll as Time Code on DAT is continuous.
TC has to be transmitted to the slate.
Someone has to watch that the numbers on the slate are rolling and are correct
• advantage is that you can use inaccurate TC generators in your Recorder.
• Some recorders only have a relatively inaccurate TC generator. Record run Time code eliminates the need to pre roll (the 10 sec. minimum for sound only).
• Error possibility: Since the time code visible on the slate does not move until it is refreshed by the generator from the DAT telecine operators need to know not to take the first visible frame of time code on the slate to punch into your telecine controller.
• They must wait until they have moving code and pick any of those frames.
• Editors like the continuous TC on the DAT as it lets them find takes easier in post sound
• When I record with DAT, I normally use REC RUN and keep the ID Write in manual mode. I can then write an ID just prior to pre-slating. This way, it looks to post as if I never stopped when I roll for the actual take, which is only a new start for the recorder but a continuous TC.
• In real time it might be thirty minutes after pre-slating though. The time code is continuous and the ID# does not advance.
• This allows me to slate, log the take number and ID# long before I call "speed". Al I need to do for me to call speed is to press the record button and hear the confidence monitor playback.
• I transmit the TC to slate and don't have to worry about excessive pre rolls that waste tape and there is plenty of pre-rolled TC for telecine as all TC is continuous.
Advantages of RECORD RUN Time code
• No drift, no wrong code due to wrong switch settings. When transmitting to a slate that has no TC generator (or at least a disabled one), the numbers on the slate can only be the ones being recorded.
• Instant speed, no pre-roll required. When using REC RUN, the pre-roll is built into the previous take.
• Time code is uninterrupted from the beginning of the tape to the end.
• No worrying about resetting or re-jamming time code after a battery change or power loss in recorder or video camera
• No need to re-jam slate every 4 hours to compensate for drift.
• When using 1-hour tapes, 24 consecutive tapes can have unique, non repeated time code. Makes it easier for post to find takes. Makes final post bookkeeping nice and neat, saves them from having to read labels on tapes.
• When the slate numbers are rolling, the cameraman can assume you have speed
• If the slate numbers are not rolling, the camera-assistant (Slate person) or maybe even the operator can assume you don't have speed.
• Assuming they pay attention is giving away a lot of your responsibility. You might be screwing up totally and no one notices. You better have a good monitor!
This is a straightforward mechanical resolving situation;
picture and sound are lined up manually in a synchronizer and kept mechanically parallel as usual for the last 60 or so years. No pre-roll necessary.
No time code is needed here, unless DAW editing systems are used.
If you are using a DAT be very careful about setting Ids on the DAT correctly and Logging them
As much as I love transfer technicians, they tend to be underpaid and over worked….need I say more?
They often work with machines that mute in fast forward or have a scan with unusable audio.
29.97nd / 29.97drop NTSC videotape Dailies
Transfer picture to NTSC tape running at a standard 29.97 Fr/Sec: Picture is transferred using 3/2 pull down to expose 30 frames (60 fields) of video in the same second that 24 film frames were exposed originally. The 3 and 2 refer to the process where one film frame is transferred to 2 video fields and the next film frame is transferred to 3 video fields. This process adds the 12 additional fields (6 frames) needed to make 30 out of 24. This is how ARRI shows it schematically on their website www.arri.com/infodown/cam/ti/p-1008.pdf
The 4 film frames are called ABCD the corresponding video frames A1,A2,B1,B2,B3, etc.
So far so good. Now you have 30 frame video from 24 frame film.
Now this is slowed by 0.1% to compensate for color video's real speed of 29.97 Fr/Sec.
Sound follows this slow-down (“pull-down”) of 0.1% to 29.97.
In telecine transfer, the colorist parks the picture on an easy to read time code number. The number is then punched in the telecine computer and all is automatic from then on. It is here where the sound playback machine (¼ inch or DAT) needs the 10 or so seconds to come up to perfect video speed. Videotape dailies get a new TC starting with 1:00:00 at tape roll 1. An EDL is kept to track original location TC, film negative footage (keycode), and the new telecine TC. An EDL (edit decision list) is a database file on a computer disk that accompanies the video tape from then on and is imported in the editing computer.
How To Stay In Sync With HD Cameras
23-frame time code
Just as we were getting used to having to contend with pull-ups and downs when dealing with a 24-frame film shoot, we get another headache. HD actual time code rate is 23.976 fps. It is also referred to as 23.98 fps. Since there is no 23.976 frame rate selection, the problem actually lends itself to a simplified solution .
Because most video workstations and edit bays perform in the NTSC 29.97fps format, the HD picture must be down-converted to NTSC. There is no problem converting 23.976 fps to 29.97 fps. These two frame rates are closely related to each other, and the conversion works perfectly. Since 23.976 is a workable solution, it also means there is no .1% slow down (that we have all come to know and hate) from shooting with 24-frame film. No speed change for picture. So what about the time code for sound?
If you are running a DAT recorder and want to have the same time code on audio as you have running in the camera in a “Free Run” (time of day) situation, you can cross jam 23.976 to 29.97 fps from camera to audio.
In this scenario, the camera acts as the master time code.
To do this, you will have to use a Synch Box, or a time code generator/reader.
Whichever one you choose to use, set it to 29.97 fps and jam sync it from the 23.976 fps of the camera. The camera will have a BNC connector for time code output. feed the 29.97 fps into your DAT recorder from the Synch box.
Have your DAT recorder set to 29.97 fps.
If you are still running a time code slate, make sure that it is set to 29.97 fps as well when you jam it from the DAT recorder.
Now that sound is running 29.97 fps and camera at 23.976, what happens at the end of the day? As stated earlier, the picture must be down converted if it is to be edited in video (NTSC) on a non-linear system like the AVID. During the down conversion process, the 23.976 fps is converted to 29.97 fps and a window burn-in of 23.976 fps is created for reference. Now the 29.97 picture time code is frame accurate with the production audio time code and is easily synched for editing.
When using this method in the field, there are a few things to watch out for.
• When some HD cameras changes batteries or is powered down in any way, you must jam sync again!
• Changing the batteries creates a time code skip and suddenly you will have a possible 6 frame offset between sound and picture.
• There must be excellent communication between camera and sound on this. Most HD cameras will not lose frames when put on standby.
Without the TriSync, there is the possibility of a 1 frame offset, no more than that.
sync reference is used in a camera to accurately define each frame. (frame sync)
NTSC analog video, has the sync signal consisting of a Blanking Pulse
+ color burst + back porch) followed by the video image data. This sync information is repeated every scan line.
Tri-Level Sync systems
Generally used in Multi camera setting only.
• Ambient Tri-level "Lockit" boxes (ACL 202CT) delivers time code with a built-in Tri-level sync generator.
• Denecke was released, their Tri-level Syncbox model SB-T.
Provides seamless Camera ( picture switching for HD & SD systems ) High Definition camcorders cannot Genlock to a standard NTSC or PAL video sync signal. HD uses Tri-level sync. The Tri-level sync signal consists of a three-level sync pulse
(zero volt (0V) Blank, -0.3 V pulse
, +0.3 V pulse) followed by the video image data. The signal is repeated for every scan line while it creates the entire HD frame.
But there are other reasons to employ genlocking, apart from its more traditional use in live switching multi-camera productions.
If you just jam, or cross-jam, time code in respect to itself only, you can get up to a one-frame difference between the camcorders in a multi-camera set up. Or in other words, this means that the time code numbers might be out of step with each other, by up to one frame, in any multi-camera set up.
Using time code that is linked to camera sync in a fixed relationship, eliminates this random time code offset problem. A simple jamming operation doesn't establish a precise relationship between the time code and camcorder sync. It is random within a single frame.
When jamming time code with a Tri-level "Lockit" box, you are jamming the time code in respect to a reference source of Tri-level sync. In other words, the advancing time code numbers are timed to run in a precise relationship with the sync stream.
This means that as the camcorder begins to built a new frame, the time code advances to the next frame number, at that precise moment in time. As every new frame starts, the next time code number appears at precisely the same moment.
When you jam these new Tri-level "Lockit" boxes in respect to each other, you are not only getting the time code numbers to roll in perfect step with each other, but you are also getting the Tri-level sync stream in perfect step with each other.
There are many issues to pay attention to regarding sync sound for an HD production. Communication is the most important part, but with everybody using the same game plan all should be good. Working with 23.976 fps there is no pull-down with 29.97 fps, - no .1% pull-down problems.