Ralph Aichinger <[email protected]> wrote: > Rob <[email protected]> wrote: >> I think the average internet connection from a device like an iPhone >> has so much jitter that this approach will not work reasonably well. >> (try to ping to an internet server and see what kind of jitter you >> have, it usually is terrible over UMTS, WiFi etc) > > iPhones do have a GPS though, and there do exist apps (at least > for Android, supposedly also for the iPhone) that sync time > to this GPS.
I have no knowledge of the internal architecture of the iphone, but when this GPS receiver is internally connected using an emulated serial link that transfers NMEA packets, the accuracy of that time sync also will leave a lot to be desired. Fine for wristwatch time, not so good for measurements and calibrations. For that you need PPS information, which is usually not provided in designs not especially made for timekeeping. When you want accurate measurements, you need to run an ntpd process on the machine that continually averages the information from the GPS and disciplines the local clock using a slow loop, and then perform the measurement relative to this disciplined local clock. That way you avoid the jitter of individual GPS time readings. That said, I find it hard to believe that the same measurement cannot be done relative to the standard iphone local clock with enough accuracy for the original poster. Clocks tend to run quite accurately when compared to the precision required for typical audio applications. _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
