[email protected] wrote:
small packets. A calibration run would consist of an initial NTP syncronization with an audio packet, followed by a period of some
What you are describing here isn't, I think, the use of NTP, but the use of SNTP. You seem to be making a measurement, form the server, over a short amount of time. True NTP measures frequency and time and does so over time periods long compared with the network and scheduling jitter.
number of minutes during which I will just count audio packets, followed by a final NTP synchronization with the last audio packet. By knowing the time difference over some number of audio packets I hope to calculate the actual audio clock frequency for that device.
The way to do it with NTP is to discipline the main clock frequency, over many hours, and then measure the time relative ot the system clock. You may well find that you don't have to measure the sound generator frequency because it may use the same crystal as the main clock.
Doing this simply, requires that you have some form of kernel discipline for the clock that is able to interpolate between ticks, allowing for the frequency correction.
If you try and do SNTP measurements at the start and end of a sort period of tone, you will be very susceptible to network delay variations.
Incidentally, given that all phone networks are digital these days, even your old method is susceptible to clock errors in the network, although I think most networks use atomic time.
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