On Wed, 06 Feb 2013 16:10:44 -0800, E-Mail Sent to this address will be added to the BlackLists <[email protected]> wrote:
>(Shrug) > >Considering that iPhones, and android phones can sync with > NTP servers just fine without an extra APP, > and the SDKs have monotonic nanosecond timers already? > As I explained in another thread last week, my app is not a time app. It is a precision audio frequency measuring app. The users of this app expect frequency accuracy on the order of 12 ppm. To achieve this accuracy I cannot rely on the nominal 100 ppm accuracy of the quartz crystal that drives the device's audio sampling rate. So I need to perform an initial calibration to determine each device's actual audio sample rate, which is quite stable, and which is totally independent of the system clock. For the past two years my app has been doing this by having the user call the NIST telephone service and letting the device listen to standard 500 Hz or 600 Hz tones to determine the calibration factor. But this is a hassle. So I am trying to achieve 12 ppm frequency calibration by developing a temporary local time stamp that is disciplined by SNTP. I figure two SNTP samples about 2 to 4 hours apart will give the required frequency accuracy, assuming typical SNTP jitter. This only needs to be done once since ongoing time accuracy is not my goal. And I hope to automate the process so the user can just start the calibration just before retiring for the night. The next day my app will be calibrated on his device and the user will not need to do that again. > I don't see how $300 can be considered low cost. It is quite simple. There are no comparable apps to mine that cost less. There are two comparable apps to mine that cost quite a bit more. > Not to mention phones with GPS, can get stratum 0 time > right from the satellite, without the asymmetrical > network latency. > > > Cell towers are already synchronized with stratum one > servers and / or GPS, and usually contain stable oscillators > e.g. rubidium, cesium, ... > > Cell towers can't do seamless handoffs for moving cell phones > to adjacent towers without close synchronization. My app also has to run on iPads without cell tower access. _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
