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Given some event in a game, what is the maximum delay to producing audio that the player will properly associate the audio with that event (and not perceive lag)?

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Not much. I'd guess it has to be less than 1/10 of a second. Though personally, I might notice it if it were more than a few frames at 60 FPS. –  Almo May 13 at 18:27
    
Don't forget that in most cases the rendered output will have some lag too, some of which will come from the monitor. It can take over 100 ms for the result of player input to be displayed on screen. See anandtech.com/show/2803 –  Adam May 13 at 22:22
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It's around 20 milliseconds when playing an instrument, around 80 milliseconds when you're a listener. This is just my personal experience, your mileage may vary. –  rwols May 13 at 23:57
    
More than any specific time you need consistency. As long as everything has the same delay you can be within reason. If everything is 100ms late you may not really notice it but if some sounds are near instant and the rest are 100ms or something inbetween then you will notice. –  0xFADE May 14 at 20:24

3 Answers 3

up vote 34 down vote accepted

The following result are calculated for lip synchronization which is concidered to be "the most noticeable a/v sync error".


Wikipedia says

For television applications, audio should lead video by no more than 15 milliseconds and audio should lag video by no more than 45 milliseconds. For film, acceptable lip sync is considered to be no more than 22 milliseconds in either direction.


The Media and Acoustics Perception Lab says

The results of the experiment determined that the average audio leading threshold for a/v sync detection was 185.19 ms, with a standard deviation of 42.32 ms


The ATSC says

At first glance it seems loose: +90 ms to -185 ms as a “Window of Acceptability”

and

  • Undetectable from -100 ms to +25 ms
  • Detectable at -125 ms & +45 ms
  • Becomes unacceptable at -185 ms & +90 ms

(– Sound delayed,+ Sound advanced)


To conclude

The results aren't so far from one another. It seems that the maximum acceptable delay is around 150ms, which is 9 frames at 60 frame per second.

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"If you have a delay, it should be the video that is delayed." seems that it should be reversed, the ATSC article clearly states that people expect/tolerate sound happening a bit after the sight (since in real life sound lags sight by approx. 1 ms per foot of distance), but don't associate events properly if video event happens after the sound. –  Peteris May 13 at 20:35
    
You are right, I completely misunderstood. Thank you. (I edited) –  Heckel May 13 at 20:46
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+1 for finding reputable sources –  Philipp May 13 at 20:59
    
I can tell you from personal experience that this even varies between ears in the same person. I have a rare vestibular condition that actually causes my brain to process auditory stimulation in my left ear measurably delayed vs. the right ear. On a bad day this causes dizziness, but most of the time it is tolerable. So yes, this is extremely subjective. –  Andon M. Coleman May 13 at 21:21
    
Where do you get 150ms? Your sources clearly average around 45ms. –  Miles Rout May 15 at 0:25

It depends of the event

Feeling that, say, an explosion you see and hear is a single event will have the tolerances described in other answers - no more than ~50ms; some people may be more sensitive (e.g., amateur musicians), so I'd suggest to aim at 30ms or no more than 2 frames at 60fps.

I believe that the perceived distance should affect those tolerances. People expect far sounds to be slightly delayed, since in real life sound lags sight by approximately 1ms per each foot of distance. So an explosion on an zoomed out RTS game 'map' might have a larger tolerance for sound lag than the player firing their own gun in an FPS.

Specialized cases, such as having a proper feel for a music/rythm game may require much tighter tolerances, 15-20ms or even lower - for example, if the player hears both the "input action" such as singing into a mic or banging a plastic instrument, and also a sound generated by your system for the same event, then a 50ms lag will cause the "original" and "played" sounds to mix weirdly.

In addition, keep in mind the lag between start of the audio file and the "event" inside that audio file - in many audio clips, the "event" won't be right on the edge, you may have a sound of a lightning strike where the 'strike' happens 200ms after the beginning, which would be obvious to everyone, and pretty much all sound files, even a drum-hit, will have some delay there.

Don't measure averages - look at worst case

Sight&hearing are deeply connected in human perception, and if one of them stutters relatively to other, then it will be perceivable. It's not okay if most of the time it's very fast but occasionally there's a 0.2 second delay while something is loading - people will notice such situations. This is why audio is often kept running on a separate thread, isolated from the other activities and just getting rapid notifications on what preloaded clips should be played.

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For games which require a person to react to audio cues, every millisecond by which the sound is delayed will cause the person's response to likewise be delayed. Someone who is simply watching a movie or cut-scene may not notice too much if the audio and video aren't exactly in sync, but it's often important and sometimes critical that audio be in sync with what the player is expected to be doing.

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