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?

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.

{
  "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"
    }
  ]
}