sighting of UFO phenomena

Well, how to put this.....
In all UFO sightings I wonder if people noticed sound from the source always come later then picture, it is normal when watching airplane or any other far object. You must see it going over sky above your head but hear it on the spot which is always late and behind that object.

This can be used in measuring the altitude and distance from observer.

But what is more stranger is when this doesn't happen.
I have read that thre were sightings in which sound and visual were synchronized but object were far and visible. How was that?
I also read that this is known as electrophonics, and it is connected with plasma discharge.
Also in those cases we can think there were halucinations, because audio visual latence doesn't exist.

A lot of this can be blamed on untrained observers, as your average Joe seeing a UFO isn't likely thinking about such things, and so doesn't recall the detail as important. He remembers what the sound sounded like, but not necessarily when it was first heard.

Also, in many encounters, the UFO is not that high, and so it's likely the time between sound and sighting goes unnoticed by the untrained observer...so when the sighting is described, it doesn't enter into it....

Well, in most of sightings UFOs are flying ultrafast multiple speed of sound, so it has to be great distance from visual and audio picture.
If we have UFO flying on altitude 500m with 1 mach then in 1.5 seconds which is time needed for sounf to come it goes 45 degrees in the field of sight so it is very easy to notice the difference.
Even for a child is easy to notice that even for a passenger aiplane which speed is not significant it is not at the point where we heard him.
So this has to be part of sighting or it was halucination or just visual sighting.
Sound of UFO is probably of bigger importance for thay have to be propelled by some engine?

Most observers report no sound at all, or at the very least, some kind of a humming sound (and this is only in very low altitude sightings).