# What do ITU-R BT.1359-1 detectability and acceptability thresholds say about audio leading versus lagging picture, and which sign convention does it use?

- id: art_01M5NP7JA83Q3QHQW5PCTQSKYD
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T10, T13, T20 · tags: none
- updated: 2026-10-24T00:51:04.130Z
- url: https://veyrul.com/articles/art_01M5NP7JA83Q3QHQW5PCTQSKYD

Problem: viewers tolerate audio lag and audio lead very differently, so a single symmetric +/- figure misleads. Conditions: broadcast television; thresholds are averages from subjective tests, original (1998) Recommendation. Method: BT.1359-1 states detectability thresholds of about +45 ms to -125 ms and acceptability thresholds of about +90 ms to -185 ms on average, where a POSITIVE value means sound is advanced (early) relative to vision. It recommends an overall sound/picture tolerance of +90 / -185 ms, +25 / -100 ms between image source and the zero reference, and +22.5 / -30 ms from final source selection to the transmitter input, with no downstream segment outside the broadcaster's control adding more than +/-2 ms. Its appendix explains the 22.5/30 ms limits as half a grade point above the detectability threshold on the five-point scale (one grade is about 60 ms for sound delay, about 45 ms for sound lead). Practical reading (inference): audio that lags picture is detected lat...

Problem: viewers tolerate audio lag and audio lead very differently, so a single symmetric +/- figure misleads. Conditions: broadcast television; thresholds are averages from subjective tests, original (1998) Recommendation. Method: BT.1359-1 states detectability thresholds of about +45 ms to -125 ms and acceptability thresholds of about +90 ms to -185 ms on average, where a POSITIVE value means sound is advanced (early) relative to vision. It recommends an overall sound/picture tolerance of +90 / -185 ms, +25 / -100 ms between image source and the zero reference, and +22.5 / -30 ms from final source selection to the transmitter input, with no downstream segment outside the broadcaster's control adding more than +/-2 ms. Its appendix explains the 22.5/30 ms limits as half a grade point above the detectability threshold on the five-point scale (one grade is about 60 ms for sound delay, about 45 ms for sound lead). Practical reading (inference): audio that lags picture is detected later than audio that leads it, so when an offset cannot be removed exactly, a small lag error is the less visible one; but the Recommendation states limits, not a preference. Failure modes: reading BT.1359 positive as 'delay' (it means advance), or R37 table columns as BT.1359 signs; applying acceptability figures (+90/-185) as a quality target when they are outer limits. Limitations: tests used NTSC/PAL material; the Recommendation also notes film at 24 fps should be within about half a frame (about +/-22 ms). Version: BT.1359-1 (1998).

Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.

Limitations: Averages from older tests; the 'lag is less visible' reading is my inference from the asymmetric thresholds. Sign conventions differ between documents, so state the convention in any report.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1359-1-199811-I!!PDF-E.pdf",
      "note": "considering g); considering g; recommends 4"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Problem: viewers tolerate audio lag and audio lead very differently, so a single symmetric +/- figure misleads. Conditions: broadcast television; thresholds are averages from subjective tests, original (1998) Recommendation. Method: BT.1359-1 states detectability thresholds of about +45 ms to -125 ms and acceptability thresholds of about +90 ms to -185 ms on average, where a POSITIVE value means sound is advanced (early) relative to vision. It recommends an overall sound/picture tolerance of +90 / -185 ms, +25 / -100 ms between image source and the zero reference, and +22.5 / -30 ms from final source selection to the transmitter input, with no downstream segment outside the broadcaster's control adding more than +/-2 ms. Its appendix explains the 22.5/30 ms limits as half a grade point above the detectability threshold on the five-point scale (one grade is about 60 ms for sound delay, about 45 ms for sound lead). Practical reading (inference): audio that lags picture is detected later than audio that leads it, so when an offset cannot be removed exactly, a small lag error is the less visible one; but the Recommendation states limits, not a preference. Failure modes: reading BT.1359 positive as 'delay' (it means advance), or R37 table columns as BT.1359 signs; applying acceptability figures (+90/-185) as a quality target when they are outer limits. Limitations: tests used NTSC/PAL material; the Recommendation also notes film at 24 fps should be within about half a frame (about +/-22 ms). Version: BT.1359-1 (1998). · locator: considering g); considering g; recommends 4 · source: https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1359-1-199811-I!!PDF-E.pdf

Rights:
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