Fields, Frames & Sync

by Pam Malouf-Cundy

	Sound effects editor to picture editor: "The picture was cut great and all the lists were fine, but there were a lot of clipped tracks..."
	Shocked picture editor: "What?!? I am meticulous with all my tracks' cuts, there's no way!"

Not! Check out the diagram on the right. You may have cut out on frame B, but as soon as you put out a sound list the cut has to occur on a video frame, so part of frame C may be included in your edit in the list!

Yes, the Avid and Lightworks allow us to make wonderful track cuts based on 24 fps film, but once we're locked (whether we're finishing on film or tape) our edits get put out onto a sound EDL. This "secondary time code list" (the numbers that correspond to the original sound daily rolls - usually 1/4" or Dat) is made up of start and stop numbers based on 30 fps time codes. In other words, the edits we made based on 24 fps are all translated to a list based on 30 fps. ( Even on shows with an all-film finish.) At any point, a track cut in the list can be up to 3 fields (1 & 1/2 frames) off from where you actually intended it to be! (Same overall duration.)

What! Why, you ask! With a ratio of 24 film frames to 30 video frames, a 6 frame film edit corresponds exactly to a 7 Þ frame video edit. But, video edits cannot include partial video frames (less than 2 fields) therefore the corresponding video edit must be either 7 or 8 video frames long. (Remember, with 35mm 4 perf picture - each film frame must have it's own 4 perforations per frame, and similarly, each video frame must have it's own two fields.) Based on durations and time codes, the digital editing systems add or subtract a video frame to match as closely as possible to the editor's film cut list. Not accurate enough when we know we've made critical sound edits cutting between words of dialogue, etc.!

We can't change this technical fact, but there are a few things you can do to minimize the negative affects.

First, inform your sound editors so that they don't go around saying that all your dialogue tracks are clipped! (Reputation is everything in Hollywood. Ha.) Besides, we need the sound editor to listen for and fix these unintentional bad track cuts. Secondly, as you make track cuts throughout your editing - by being aware of this - you can eliminate many potential clipped tracks. If you don't have to cut right on modulation - adjust the track cut by a frame - knowing that if 2 fields are cut off (exchanged) in the sound list, your track cut will still be good. The exact in or out will never be off by more than 2 fields (one video frame) but the totality, taking both sides of the cut into consideration, could have a difference of up to 3 fields.