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

David McGaw n1hac at dartmouth.edu
Wed Apr 1 23:20:19 EDT 2015

There is evidence that the ear can discern differences in timing down to 
the uS range.  See a discussion by David Blackmer of DBX and Earthworks:


David McGaw

On 4/1/15 7:11 PM, Chris Albertson wrote:
> 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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