What do I do on the set?
Until modern audio recorders support the 23.976 frame rate all we can do is "Cross Jam." What is really important here is that the jam sync occurs on the "00" frame. The zero frame is the start of the second (real time or not). All Denecke products have always done this so there is no problem there. If your recorder jams on the zero frame, i.e. Nagra IV-STC, then you can cross jam directly without having to use one of our boxes. HHB and PD-4 owners can cross jam using the Denecke Syncbox or GR-1. Simply feed the 23.976 TC out of the HD Camera and into the Syncbox or GR-1 set to 29.97 Non Drop and jam sync them as usual. Then simply take the 29.97 code over to your recorder (set to 29.97 Non Drop) and jam sync or external feed the recorder with the Syncbox or GR-1.
The Time Code Slate is handled in the same fashion. Set it to 29.97 and jam it either from the camera or the cross-jammed Syncbox or GR-1. Treat this as a 29.97 video shoot. Keep in mind that this procedure only works for Free Run / Time of Day shoots. Be aware that if the camera is powered down for a battery change, etc. then the camera code will not be concurrent when powered back up. In this case you will need to re-jam everything. As always, communication is very important between the camera and sound departments!
An alternate method and the simplest way for Free Run shoots is to feed external code to the HD camera. This is useful in multi-camera shoots. Jam sync a Syncbox set at 23.976 to your recorder set at 29.97 ND. Attach the Syncbox to the camera and feed it the Syncbox code. A software upgrade is available for all the Denecke Products (TCXO preferred for high stability) to enable the generation of 23.976 fps. The catch is that HD cameras want to see Tri-Level Sync + Time Code for absolute frame accuracy. When feeding external time code only, without Tri-Level sync reference, the camera can be in sync or one frame off but not more than that. This can easily be corrected in post, especially when using a Time Code Slate. When external sync is fed to HD cameras, this sync becomes the master reference for the camera and must be extremely stable.
Another option is to ignore the 23.976 on the camera completely. Run your audio recorder with Time of Day (29.97fps) and jam sync your slate as usual. You can take the output of a Syncbox that has been jammed to your recorder (29.97fps) and feed it into track 2 of the HD camera that can be used in editorial. The audio will stay at 29.970 fps when it is transferred. Ed Novick used this method on the Spider Man movie with no problems. Also, you don't have to worry about the camera being powered down. Just make sure to communicate with post so they don't get mixed up with the time code on the HD camera audio track!
Record/Run time code is a bit more complicated. The 23.976 TC can be sent via RF or hard wired to the Syncbox or GR-1 (set to 29.97ND). It is necessary to re-jam at the start of each take since the time code clock is stopped when the camera isn't running film. The re-jam process is automatic with a GR-1 in Jam Continuous mode (JC). The GR-1 locks on to the next valid (00) frame anytime there is a break in the time code clock (camera stopped).
What is the Evertz After Burner?
The Evertz After Burner converts 23.976 fps video to 29.970 fps NTSC video. The time code clock is also converted from 23.976 fps to 29.970 fps. This is a rackmount unit that requires AC power. There is a 5 frame offset during the conversion to 29.97, but this can be handled in post. The drawback is that you have to be hard wired (at least for the video feed). There should be a corresponding audio delay to compensate for the video delay. Check out the Evertz website at www.evertz.com for more information.
What is Tri-Level sync?
The NTSC video signal consists of a Blanking Pulse (sync pulse + color burst + back porch) followed by the video image data. This signal is repeated every scan line (525 NTSC, 625 PAL) to make up the video frame. High Definition video uses what is called Tri-level sync. This signal consists of a three level sync pulse (0 V Blank, -.3 mV pulse, +.3 mV pulse) followed by the video image data. This signal is repeated every scan line to make up the video frame. HD cameras do not genlock or reference to a NTSC/PAL video sync signal.
What all of this means.
Understanding the 3-2 pulldown and how 24 fps and 30 fps relate it is easy to see how 23.976 fps and 29.970 fps relate as well. Don't be confused by these "new" numbers. 23.976 fps is used so that down conversion for contemporary video assist is a simple real time matter. The good news is that there really is nothing new. As always, communication between camera and sound departments is very important! Detailed explanations on the 3-2 pulldown transfer of 24fps film to 29.97fps video are available in the books "Using Time Code In The Reel World III" by Jim Tanenbaum or "Sync Sound With The New Media" by Wolf Seeberg. Wolf's book, "24P for Sound & Video Assist," covers the Sony HDW-F900 HD camera.
By Charles Parra, Denecke Inc.
Courtesy of Denecke, Inc.
Many thanks to Ray Cymoszinski for his invaluable help and guidance.
