Timecode and sync explained, with an LTC test file

By James Jones, founder of Granary Digital · Updated 5 November 2026

What timecode does

Timecode gives each frame a number in the form hours:minutes:seconds:frames. If the camera and the recorder carry the same timecode, the sound and the picture line up in the edit without anyone clapping a slate for each take. The slate still matters as a backup, and it is the first thing to check if the timecode disagrees with the clock.

Linear timecode (LTC)

LTC is timecode recorded as an audio signal. It is a tone that changes in a regular pattern, so the timecode can sit on a track alongside the sound. A device reads the tone and follows the time. Because it is an audio signal, it travels on the same cables as audio.

Play it back at a middle level. Both very low and very high levels distort it, and the reader then drops out. Keep it away from other audio tracks, because crosstalk can corrupt it. Do not apply noise reduction, EQ or compression to a timecode track.

Frame rates

• 25 fps is the UK standard for PAL-based production, and the normal choice here.
• 24 fps is the film rate. Use it for a 24 frames per second project, and set every device to 24.
• 29.97 fps is the NTSC rate, and it uses drop-frame. Drop-frame skips the frame numbers 00 and 01 at the start of each minute, except every tenth minute, so the timecode stays close to the clock.
• 30 fps is a separate rate, not a drop-frame setting.

Worked example

The camera is set to 25 fps and starts a take at 10:00:00:00. The recorder is set to 25 fps non-drop and jammed from the same source. After two minutes of running, both read 10:02:00:00. If the recorder were set to 24 fps while the camera ran at 25, the two would label frames differently and the edit software could not line them up on timecode.

Using the test file

The test file is 60 seconds of LTC at 25 frames per second, starting at 10:00:00:00, recorded at -12 dBFS. Use it to check a recorder before the day:

1. Connect the file's output to the recorder's line input, at the level the recorder expects.
2. Set the recorder to 25 fps non-drop and turn off any noise reduction on its timecode channel.
3. Record 30 seconds. Check that it reads the same timecode as the file.
4. Play back and check the timecode counts on in step with the clock, and that the frames increase without skipping.

If the recorder reads a different frame rate, change its setting, not the file.

Common mistakes

• Setting the camera to 24 fps and the recorder to 25. The two drift apart all day.
• Using drop-frame timecode at 25 fps, or mixing 29.97 with 30.
• Recording LTC at a level that clips, or so low that the reader loses it.
• Trusting the timecode without checking the slate. A device that lost its signal can show a plausible time that is wrong.

Where it fits

For remote sessions, our published ADR delivery spec plays the picture from the DAW timeline at the project frame rate, with timecode burnt in. For the audio side, read location sound starter: boom, lav and room tone and lav placement guide.

Sources

• Wikipedia, Linear timecode, read 5 November 2026
• Wikipedia, SMPTE timecode, read 5 November 2026

Related guides

• Location sound starter: boom, lav, room tone
• Lav placement: where to clip a lavalier microphone
• Sound report template, with a worked example
• Audio test pack: tones, pink noise and sweeps
• How does remote ADR work?
• All guides and tools

The picture at the top of this page is an illustration, not a photograph of a client or a real job.