Convert audio delay between frames, milliseconds and metres, and check it against the EBU R37 and ITU-R BT.1359 limits.
Edit any one of the three; the others follow. "Metres of air" is how far sound travels in that time, handy for speakers, stage mics and stadiums.
Viewers are far more sensitive to sound that arrives before the picture than to sound that arrives after it, which is why every standard below is asymmetric. This calculator converts between frames, milliseconds and distance, then tells you where your number falls.
40 ms and lag it by no more than 60 ms.45 ms early and 125 ms late. Its wider acceptability limits are about 90 ms early and 185 ms late.Treat these as guidelines for the whole chain: every device that buffers video, such as frame synchronisers, converters, LED processors and encoders, uses up part of the budget, and delays are usually whole frames.
One frame lasts 1000 / fps milliseconds: 40 ms at 25 fps, 33.4 ms at 29.97 fps. Sound travels about 343 m/s in air at 20 °C, so one frame at 25 fps corresponds to roughly 13.7 metres. That is why a microphone far from a stage, or a speaker far from the audience, throws sound out of sync with the picture.
If the audio is late, delay the video by the same amount, or advance the audio if your mixer allows it. If the audio is early, delay the audio, which most consoles, routers and embedders can do per channel. Measure with a proper sync test signal where you can, and treat any calculator as a starting point.
Limits: EBU R37 (+40 ms / −60 ms) and ITU-R BT.1359 detectability thresholds (+45 ms / −125 ms), as widely cited. These are recommendations, so check the current texts before using them in a specification.
EBU R37 recommends audio no more than 40 ms ahead of the picture and no more than 60 ms behind it. ITU-R BT.1359 puts the point where errors are reliably noticed at about 45 ms early and 125 ms late.
In real life, sound always reaches us after light, so late audio looks natural and early audio never does. People tolerate lateness far better, which is why the limits are asymmetric.
It depends on the frame rate: exactly 1 frame at 25 fps, about 1.2 frames at 29.97 fps and 2 frames at 50 fps. The calculator converts it for any common rate.
Add the same delay to the audio path, or reduce it on the video path. If a device adds 3 frames of video latency at 25 fps, delay the audio by 120 ms.
Sound travels slightly faster in warmer air, about 0.6 m/s per °C. It matters only for distance calculations, such as stadiums and outside broadcasts.
No. Everything is calculated in your browser.
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