Apple Cinema Tools 4 - Manual (Page 37)

Synchronization Basics
Synchronizing the audio with the video image can be fairly easy as long as some care
was taken during the shoot. There are two aspects to synchronizing your audio:
establishing sync at a particular point in each clip, and playing the audio at the correct
speed so that it stays in sync.
While shooting, you must provide visible and audible cues to sync on. The most common
method is to use a clapper board (also called a slate or sticks) at the beginning of each
take. Even better, you can use a timecode slate that displays the sound recorder’s timecode.
To sync the audio with the video, position the video at the first frame where the slate is
closed, then locate the sound (or timecode) of the related audio. Note that production
requirements occasionally require the slate to occur at the end of the take, generally with
the slate held upside down.
Because the film is often either slightly sped up or slowed down during the telecine
transfer, the audio must also have its speed changed. If the audio is being synced during
the transfer, the speed change is handled there. If the audio is being synced to the
videotape after the transfer, the speed change must happen then.
Synchronizing During the Telecine Transfer
During the shoot, you typically start the sound recorder a little before the camera rolls
and stop it a little after the camera stops. Because you end up recording more audio than
film, you cannot play the audio tape and the film through several takes and have them
stay in sync. If you want the telecine transfer to record synchronized audio on the
videotape, you must either use the scene-and-take transfer method, synchronizing each
take on its own, or create a synced sound roll before performing a camera-roll transfer.
A large benefit to synchronizing during the telecine transfer, aside from having videotapes
with synchronized audio ready to be captured, is that the telecine log usually includes
the audio timecode and sound roll number information. Importing the log into
Cinema Tools makes it possible to export an audio EDL so that an audio post-production
facility can recapture the audio clips at a higher quality later, if needed.
• NTSC transfers: When transferring film to NTSC video, it is always necessary to run the
film 0.1 percent slower than 24 fps (23.976 fps, typically referred to as 23.98 fps) to
compensate for NTSC video’s actual frame rate of 29.97 fps (instead of an ideal 30 fps).
Because the film has been slowed down, audio too must be slowed to maintain sync.
• PAL transfers: PAL transfers using the 24 @ 25 method (speeding up the film to 25 fps)
require that the audio also be sped up if you are syncing the audio during the telecine
transfer or if you intend to edit the video at this rate.
If you are transferring the film to video using the 24 & 1 method (recording an extra
video field every twelfth film frame), you should run the audio at its normal speed
regardless of where sync is established. Use 25 fps timecode for the audio in this case.
37 Chapter 2 Before You Begin Your Film Project