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

[Chris Albertson]

On Wed, Apr 1, 2015 at 9:33 AM, Reid Oda <reid.oda at gmail.com> wrote:
... Once we got this lock, the
> clocks were then synchronized to within a few ms of each other. I estimate
> 8 ms, but our method (listening to ticks from a homemade app) was not ultra
> accurate.


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.  Some musicians have learned to
keep in time and can hear a 20ms difference.   Most people can hear a
50 ms delay.    But as the clicks get close we hear them as one sound

If you have a computer with a microphone yo can record the clicks at
some high sample rate and then look at the spike on the audio
waveform.  This WILL sub-ms clicks.

-- 

Chris Albertson
Redondo Beach, California