In part one, we dealt with the basic issues to keep in your mind when synchronizing audio to picture. In part two, we’ll dive deeper in into some more advanced topics, and we’ll also go over some basic setups that you could use in your studio to make it a more video-friendly facility.

As I mentioned in part one, there are a few considerations to keep in mind when working with video that was originally shot on film, or when the final delivery format is film.

To recap: film is shot at 24 frames with a timing reference of 60Hz, where video is 29.97 with a timing reference of 59.94. When film is transferred to video it goes through a 3:2 field conversion. Each video frame has 2 fields. A 3:2 conversion takes each frame of film and spreads it out, alternating each frame of film between 2 or 3 fields of video. Through this process, 24 frames can be spread easily across 30 frames of video. Here’s an illustration:

But this conversion can introduce some problems. Film is shot at 60Hz reference and, when it’s transferred to video, runs slightly slower. Enter this situation. A big Hollywood producer (or perhaps a small one) asks you to create sound effects and/or music for his new big picture, shot on film, and it’s final delivery will be film. He hands you a VHS or Digital Beta tape for your work reference. (He’s not going to give you the original film, that’s for sure!). He also hands you a Hi-8 tape with some original audio shot on location, using the film timing reference. Your picture (on the tape) is slightly slow from what the final film speed will be; however the audio is at the correct speed. If you try to run them together and “in sync” it won’t work, because your audio was recorded using a faster reference. The solution to this problem is running your audio workstation at a “pull down” rate when working with your video.

Pull down? No it’s not coming down from the bar after a chin up. It’s running your sample rate slightly slower. A 48,000 Hz sample rate when “pulled down” becomes 47,952 Hz. That’s exactly 0.1% slower, the same difference between your film (60) and video (59.94) timing references talked about in part one. All your new audio should be recorded at the pulled down sample rate. When you are finally ready to print your audio back to DAT or digital multi-track deck from your final mix, set the sample rate back to plain old 48 kHz. The audio will be sped up exactly 0.1%, and now be running at film speed once again. Your audio tape, the one that you hand back to the Big Hollywood Producer, will run perfectly with his film. Everyone’s happy, and you get your check!

Another scenario is similar to the above, where you get a video, but the main difference being that you have no original audio to work with-- you create it all within your studio. You decide to run your audio workstation at 48kHz when working with video. When printing to your final delivery format, you now switch your workstation to “pull up”. That 48kHz now becomes 48.048kHz and your audio that was recorded in sync to the slower video timing reference will now be sped up to film speed. The catch about “pull up” and “pull down” is planning ahead for them. Be sure that you know where your audio is from, and what format is it going to.

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