On 1 October 2011 00:11, RLScott <[email protected]> wrote: > I also have a need for accurate NTP embedded into my app. I am > writing a very accurate musical instrument tuner. One of the things > that such an app needs to do is to calibrate the device to compensate > for variations in the sound system's quartz crystal time base. On > another platform I did this by having the user call up the NIST's free > time and frequency standard service on a wired phone and let my app > listen to the 500 Hz or 600 Hz reference tones. But that is a pain > for the user. I would like to offer a alternative NTP method of doing > this for devices that have occasional broadband internet connection.. > My idea is to sample NTP time at the same time that I start counting > audio packets coming in from the sound API. Then after some time > (maybe 10 minutes) sample NTP again. By knowing the difference in NTP > time and the number of audio packets processed I can find the > necessary calibration for that device. The accuracy I am looking for > is 1 part in 200,000.
I am not sure what kind of instruments are you tuning, but since basic crystal oscillator accuracy is in between 10^(-5) and 10^(-4) for audible frequencies this seems as accurate as one would need. > For a 10-minute sample interval that translates > to a total time accuracy of 3 msec. Please keep in mind that A/C conversion delay and application jitter caused by Garbage Collection will have effects of magnitude of tens of milliseconds. > If that is difficult to do with > NTP then I could extend my sample time to 100 minutes. Then I would > only need 30 msec. time accuracy. But the longer I make the sample > period the more of a pain it becomes for the user, even if he only has > to do this once when the app is first installed. Can anyone tell me > if embedding NTP into my app is likely to serve this purpose? NTP over public networks will give you at most 10s of milliseconds accuracy too and its main use is time synchronisation (making sure that 2 timestamps by distributed machines are as close as possible), rather than establishing how accurate your internal time source is. I don't want to discredit your solution and as I said above, I don't know much about the problem that you are trying to solve, but I simply think that modern quartz oscillators will offer you as much accuracy as you need for audio tuning. Daniel > > On Sep 30, 2:48 pm, Jim Graham <[email protected]> wrote: >> On Wed, Sep 28, 2011 at 11:52:18AM -0700, cool_zack wrote: >> >> > I want to get UTC time. It should not change except for tiny >> > adjustments that happen from Network. User modifications to the time >> > on the device must not affect it. >> >> What you're asking for is SNTP (often abbreviated as NTP). If all you >> need is an app, search in the market for NTP. Most of the NTP apps >> will set your device's clock (requires root). >> >> There's an app, called "UTC Time" which displays local time and UTC >> side by side. With a rooted device, it will also keep your device's >> time set to whichever SNTP server you have it configured for. >> >> If you need this for an app you're writing, let me know what you find, >> as I have some ideas along that line, myself...... >> >> Later, >> --jim >> >> -- >> THE SCORE: ME: 2 CANCER: 0 >> 73 DE N5IAL (/4) | Remember your spelling rules, including: >> [email protected] | I before E except after C >> < Running FreeBSD 7.0 > | >> ICBM / Hurricane: | BEING a native-born American, I don't >> 30.44406N 86.59909W | always notice our WEIRD spelling.... >> >> Android Apps Listing athttp://www.jstrack.org/barcodes.html > > -- > You received this message because you are subscribed to the Google > Groups "Android Developers" group. > To post to this group, send email to [email protected] > To unsubscribe from this group, send email to > [email protected] > For more options, visit this group at > http://groups.google.com/group/android-developers?hl=en > -- Daniel Drozdzewski -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
