Audio Considerations

Because the audio for a film is recorded separately on a sound recorder, there are a number of issues that you must be aware of and plan for:

Choosing a Sound Recorder

When choosing a sound recorder, you have several options: an analog tape recorder (typically a Nagra), a Digital Audio Tape (DAT) recorder, or a digital disc recorder. Whether analog or digital, make sure the recorder has timecode capability.

Choosing an Audio Timecode Format

Unlike video or film, which must be structured with a specific frame rate, audio is linear with no physical frame boundaries. Adding timecode to audio is simply a way to identify points in time, making it easier to match the audio to video or film frames.

During the shoot, you have the choice of which audio timecode standard to use (typically 30 fps, 29.97 fps, 25 fps, 24 fps, or 23.98 fps). You also have the choice, with 30 fps and 29.97 fps, of using drop frame or non-drop frame timecode. For NTSC transfers, it is highly recommended that you use non-drop frame timecode for both the video and audio (although Cinema Tools can work with either). See About NTSC Timecode for more information about drop frame and non-drop frame timecode.

A consideration for the audio timecode setting is how the final audio will be mixed:

  • If the final mix is to be completed using Final Cut Pro: The setting needs to match the Final Cut Pro Editing Timebase setting in the Sequence Preset Editor.
  • If the final mix is to be completed at an audio post-production facility: The timecode needs to be compatible with the facility’s equipment.

Note: Make sure to consult with the facility and make this determination before the shoot begins.

In general, if you are syncing the audio during the telecine transfer, the timecode should match the video standard (29.97 fps for NTSC, 25 fps for PAL, or 24 fps for 24p). Check with your sound editor before you shoot to make sure the editor is comfortable with your choice.

Mixing the Final Audio

The way you mix the final audio depends on how complicated the soundtrack is (multiple tracks, sound effects, and overdubbing all add to its complexity) and your budget. You can either finish the audio with Final Cut Pro or have it finished at a post-production facility.

Finishing the Audio with Final Cut Pro

If you capture high-quality audio clips, you can finish the audio for your project with Final Cut Pro, which includes sophisticated audio editing tools. Keep in mind, however, that good audio is crucial to a good film, and a decision not to put your audio in the hands of an audio post-production facility familiar with the issues of creating audio for film might lead to disappointing results.

You can export the audio from Final Cut Pro as an Open Media Framework (OMF) file for use at an audio post-production facility. An exported OMF file contains not only the information about audio In and Out points, but also the audio itself. This means that, for example, any sound effects clips you may have added are included. When you use an OMF file, the recording quality must be as high as possible, as this is what the audience will hear. Make sure to use a good capture device and observe proper recording levels.

Exporting Audio EDLs

Another approach is to use lower-quality clips in Final Cut Pro and then export an audio Edit Decision List (EDL) for use at an audio post-production facility. There they can capture high-quality versions of the audio clips straight from the original production audio source and edit them based on the audio EDL. For this to work, the timecode and roll numbers of the original sound rolls must be kept track of and used to create the audio EDL.

Audio clips captured as part of video clips do not retain their original timecode and roll numbers, and the Final Cut Pro EDL cannot be used by an audio post-production facility. This is most common with clips created from scene-and-take transfers, where the audio is synchronized to the film and recorded onto the videotape, losing the original audio timecode. But because the telecine log from the transfer generally contains timecode and reel number information for both the video and audio, importing this log into the Cinema Tools database allows the database to track audio usage, and you can export an audio EDL from Cinema Tools once you finish editing.

See Exporting an Audio EDL for details about the process.

Synchronizing the Audio with the Video

The production audio for a film is recorded separately on a sound recorder; this is known as dual (or double) system recording. Synchronizing the audio with the film and video, ensuring good lip-sync, is a critical step in making a movie. How you synchronize depends on the equipment used and when syncing is done. There are also considerations related to your video standard, how the telecine transfer was done, and the timecode used that directly impact the process.

There are three times when audio synchronization is important:

  • During the telecine transfer

  • During editing

  • While creating the release print

Different strategies may be required to maintain sync at each of these times. Make sure you have planned accordingly.

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.

Synchronizing in Final Cut Pro

If you don’t synchronize your sound and picture onto tape via the telecine transfer, they are captured into Final Cut Pro as separate audio and video clips. You can then synchronize them in Final Cut Pro, using the clapper board shots. See Synchronization Basics for more information. After you synchronize two or more clips, you can link them together as one clip, using the Final Cut Pro merged clips feature. See Synchronizing Separately Captured Audio and Video and the Final Cut Pro documentation for more information.