[time-nuts] Striking change in iPhone time accuracy with 8.2

[Chris Albertson]

The key jingle experiment is detecting a phase difference between
ears.   I was writing about our ability to know if a sound is "in
time" with some other sound.  For example if a bass player is keeping
time with a drummer.   I figure we can do that to about 20 ms or maybe
a little better.  Apparently clicks are easier to hear.
The problem we were solving was Determining if two clocks were in sync
by listening to the ticks.

I don't think you need two iPhones to experiment with audio
perception.   A computer that can produce stereo audio and a pair of
headphones would be enough  Or a pair of speakers.  There is lots of
good quality audio software, some of it free that allows you to make
sounds with various delays.  My guess is that most people reading this
already own the required equipment, less the software.

On Wed, Apr 1, 2015 at 1:50 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
>
> albertson.chris at gmail.com said:
>> Sound travels at about 1 foot per ms.  So you can effectively delay the click
>> on one phone my placing it 8 feet farther away then the other  phone.
>> Adjust the distance until  the clicks seem to occur at the same time.   That
>> said, I doubt your ears are sensitive enough to work at the single digit ms
>> level.
>
> Your brain uses the difference in arrival times at your ears to determine
> direction.  That works better with high frequency clicks rather than low
> frequency rumbles.  You can work out how good it has to be to get reasonable
> results, but it's well below 1 ms.
>
> The usual test case is to jingle some keys.  Sit on a stool with your eyes
> closed.  Have a friend jingle the keys in various locations.  Right-left
> works well.  Up-down doesn't work very well.
>
> It would be fun to play with a pair of beeping iPhones and see what sort of
> direction they appear to be coming from.  I wonder how much the length of the
> beep influences things.
>
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
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-- 

Chris Albertson
Redondo Beach, California