[ntp:questions] Accuracy of audio tones via VOIP

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Mon Jul 15 23:06:59 UTC 2013


Robert Scott wrote:
> I am the developer of a professional piano tuning app for
>  smarthphones.  My customers are professional piano tuners.
>  Although the sound sampling rate on most smartphones is
>   very close to nominal, there is as need to calibrate each
>   device on which the app runs.  The means that I offer in
>   my app is to have the user call up the NIST tones over
>   the telephone and let the app listen to the 500 Hz or 600
>   Hz tones for 30 seconds.  The call is placed using a
>   different phone and the sound is transferred acoustically
>   by careful positioning of the microphone.  With this method
>   I have been able to achieve a frequency calibration of 6 ppm.
>   This worked fine when everyone had access to a landline phone.
>   But now with varions VOIP technologies many of my customers
>    are doing the calibration using the NIST tones through
>    a VOIP phone.  I just want to find out how much they might
>    be losing in frequency accuracy if they do this.

I don't see how this is relevant to this newsgroup / mailing list
 Mailing list for people with questions about NTP
  (gatewayed to the USENET newsgroup comp.protocols.time.ntp)?


 Perhaps closer in relevancy, although likely not relevant either:
  alt.pl.voip, uk.telcom.voip, fido7.ru.voip,
  it.tlc.telefonica.voip, xs4all.voip, hr.comp.voip


Perhaps <https://support.skype.com/en/> ?


Apparently NIST appears to have a relevant service,
 FMAS with support for $500/mo
<http://www.nist.gov/pml/div688/grp40/upload/SP-432-NIST-Time-and-Frequency-Services-2012-02-13.pdf>
<http://tf.nist.gov/general/pdf/1650.pdf>
<http://tf.nist.gov/service/pdf/calibrations.pdf>
<http://tf.nist.gov/general/pdf/2289.pdf>

I'll also note, that some piano tuners claim to have delt
 with this issue using the NIST-SIP stack.
  {Perhaps it somehow gave them access to some data,
    that let them evaluate the situation?}


Have you really been fiddling with NIST audio time tones,
 and VOIP since ~2006?

If you haven't found your answers by now without testing it yourself,
 you likely won't without testing it yourself,
 or paying someone (e.g. NIST) to do it for you.

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