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Production3 min read

LESSON 115

Audio sync and timecode

The clap, the code and the frame.

IN THIS LESSON

  1. Why sync is a problem
  2. The clapperboard
  3. Timecode
  4. Practice: syncing on a small shoot

Why sync is a problem

Film stock responds to light, not sound, so for most of cinema's history picture and sound were recorded on separate machines. Many digital productions still do this, recording sound on a dedicated recorder that has better microphones, more tracks and a separate backup. This is called double system. The two recordings must then be lined up in the edit to within a frame, or lips and words drift apart. Two tools solve this: the clapperboard and timecode. Recording sound only on the camera is called single system, and it is simpler but usually worse.

The clapperboard

The clapperboard, or slate, is a board with hinged clapper sticks across the top. The camera assistant holds it in frame with the sticks open, reads out the scene and take for the sound recording, then snaps the sticks shut. The frame where the sticks meet is easy to find in the picture, and the sharp clap is easy to find in the sound, so the editor lines them up. The two-stick clapper is credited to the Australian film-maker F. W. Thring, and the board also labels each take on both tracks.

Timecode

SMPTE timecode labels every frame with hours, minutes, seconds and frames, defined in the SMPTE 12M standard. It supports common rates including 23.976, 24, 25, 29.97 and 30. It made videotape editing possible and led to non-linear editing. It can be carried as an audio signal called linear timecode, in the video signal, in digital audio, or burnt visibly into the picture. Camera assistants log the start and end timecodes of shots, today usually with software connected to the timecode generator or camera.

Practice: syncing on a small shoot

This is working practice. Even if your cameras and recorder can share timecode, slate every take; it costs a second and saves an hour when something drifts. Set every device to the same frame rate. If you have timecode boxes, jam them to one master at the start of the day and again after lunch. Without timecode, record scratch audio on the camera so the editor's software can match waveforms automatically. Call the take numbers clearly. Keep a written sound report for each roll.

Try it today

  1. 01Make a clapper from two pieces of card if you have no slate.
  2. 02Record a short take on camera and on a separate recorder.
  3. 03Clap once in frame at the start.
  4. 04Line up the clap by hand in your editor.
  5. 05Try your editor's automatic waveform sync and compare.