PostMicroTools
Reference + calculator
Pulldown & audio sync
When footage moves between frame rates, speed and audio change. This works out the speed shift, pitch, the audio sample-rate to "pull", and how far sound drifts out of sync over time.
Common conversions
| From → To | Speed | Audio | Name |
|---|---|---|---|
| 24 → 23.976 | −0.1% | 48000 → 47952 Hz | NTSC pulldown |
| 23.976 → 24 | +0.1% | 47952 → 48000 Hz | NTSC pullup |
| 30 → 29.97 | −0.1% | pull down 0.1% | NTSC pulldown |
| 24 → 25 | +4.17% | pitch ~+0.7 st | PAL speed-up |
| 25 → 24 | −4.0% | pitch ~−0.7 st | PAL slow-down |
What is 1000/1001?
NTSC "drops" the rate by a factor of exactly 1000/1001 (≈0.0999%) for historical color-subcarrier reasons. So 24 fps becomes 23.976, 30 becomes 29.97, and 48 kHz audio paired with them is sometimes run at 47.952 kHz.
Pull vs frame-rate conversion
A "pull" just reinterprets existing frames/samples at a slightly different rate (no new frames). A true frame-rate conversion (e.g. 24→25 for content, not speed) creates new frames via blending or optical flow and is a different operation.
Cadences, 0.1% pull-down and other archive dragons
Pulldown mapping is legacy knowledge that refuses to retire, because archives and tape ingests keep arriving. Classic 2:3 pulldown distributes 4 film frames across 10 NTSC video fields (the AA-BB-BC-CD-DD cadence) to fit 23.976 material into 29.97 — and reversing it correctly (IVTC) is the difference between restoring clean progressive frames and inheriting interlace ghosting through a whole restoration.
The audio side trips people just as often: NTSC's 1000/1001 ratio means "48 kHz" material pulled down actually runs at 47 952 Hz. Sync a transfer without accounting for the 0.1% and picture and sound drift about 3.6 seconds per hour — the signature symptom of a mis-flagged telecine or a double-applied pull-down.
PAL territories have their own dragon: 24→25 by 4.1% speed-up, which shortens a 100-minute film to ~96 minutes and raises audio pitch by nearly a semitone unless corrected. This reference lays out each cadence and rate relationship so you can identify what a mystery ingest actually contains.
Is pulldown still relevant in an all-digital pipeline?
For new acquisition, rarely — cameras shoot native progressive rates. It stays essential for tape and telecine archives, restoration work, and diagnosing inherited masters where a cadence (or half of one) is baked in.
What does 0.1% audio pull-down mean in practice?
Audio recorded at 48 000 Hz is played at 47 952 Hz so it stays in sync with 23.976/29.97 picture. DAWs and NLEs apply it as a sample-rate flag; applying it twice — or not at all — produces the classic 3.6 s/hour drift.
How do I spot 2:3 pulldown in footage?
Step through fields: the cadence shows three clean frames followed by two interlaced ones (combing) in a repeating 5-frame group. Detecting the pattern — and where edits broke it — tells you whether IVTC can fully recover the progressive source.