On 28 Jan 2013 17:56:10 GMT, Rob <[email protected]> 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. It is also my experience that long term crystal stability in these devices is way better than their absolute accuracy. So a one-time calibration is a big improvement over assuming the nominal sampling frequency. As I have pointed out before, whatever the timing jitter is in a radio internet connection, a sufficiently long calibration run with a sample at the beginning and at the end can give me the required .02 cent accuracy (12 PPM). And there is every indication that the required time period will be less than the time it takes the user to get a good night's sleep. Robert Scott Hopkins, MN _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
