[ntp:questions] Using NTP to calibrate sound app

Uwe Klein uwe at klein-habertwedt.de
Tue Jan 29 09:23:56 UTC 2013


no-one at no-place.org wrote:
> On 28 Jan 2013 17:56:10 GMT, Rob <nomail at example.com> wrote:
> 
> 
>>In my opinion, when you think a crystal is not accurate enough, relying
>>on single-shot time measurements via radio internet connection will
>>*certainly* not be accurate enough.  The protocols used on radio
>>channels are not symmetric, because the topology is not symmetric.
>>(there is a single base station communicating with a number of clients)
>>
>>Typical crystal accuracy is in the same ballpark as what you require.
>>When you see significant differences, it is more likely that the actually
>>used crystal frequency is different from what you are reading from
>>some system information call.
> 
> 
> Yes, that may be true.  Smartphone manufactures, for whatever reason,
> sometimes design a sound system that delivers 22,150 samples per
> second when my app requests that more standard 22,050.  By the way,
> this has not been a problem with Apple devices (iPhone/iPad), which
> all seem to be close enough to nominal without custom calibration.
> But Android devices and Windows laptops are a different story.

Can you modify your software to be rate agnostic/flexible?
the samling rate error you show is 4000ppm while crystal deviation
should not go beyond 50 .. 100 ppm ( 1 "cent" should be ~416ppm !?)

uwe



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