[time-nuts] Discussion of precise time and frequency measurement

Will Matney xformer at citynet.net
Wed Jun 29 23:30:42 UTC 2011


What I would think that would be needed, software wise, is an app that's
similar to the long term plots used in calibration. I would say that you
know the ones I'm speaking of, as it is a graph that stretches over a month
(or longer), and lets say the horizontal center line would represent 60 Hz,
and above or below it would be how much it's off in which ever measuremet
you want, either in frequency, or in PPM. Long term time is on the
horizontal axis, and frequency+/- is the vertical. That was my thinking the
other day, so it would log any shifts over a long timespan, really similar
to the old paper plots off a frequency standard. Now whether you could use
this with a sound card, I don't know, as one would need a frequency
standard, along with the line frequency, as inputs so they could be



*********** REPLY SEPARATOR  ***********

On 6/29/2011 at 4:11 PM Chris Albertson wrote:

>On Wed, Jun 29, 2011 at 3:00 PM, Bill Dailey <docdailey at gmail.com> wrote:
>> The FireWire thing makes sense but is there some way to make the
computer itself a slave to an external source also?
>Why?   The computer has many clocks in it and they are not all derived
>all from one master.  So to answer  we'd need to know which clock you
>care about.  Obviously the clock to keep the current time of day can
>be sync'd from s master source, like GPS or an Internet NTP server.
>Maybe it's best you describe the big picture. What are you trying to do?
>But if you mean the audio interface.  Then all you really need is a
>stable clock on that.  There is an "elastic" buffer between the audio
>interface and the software so the computer can go off and do
>"whatever" for 1/10th of a second and the interface wil buffer the
>data, none gets lost as long as the buffer does not overflow.
>Modern CPUs do not run at a nice fixed rate. they are
>non-deterministic  and might execute many instructions at once or even
>out of order.   The newer Intel chips adjust their internal clock
>rates to control power use and core temperature.    If you need to
>sync to the external world then software techniques are used
>Chris Albertson
>Redondo Beach, California
>time-nuts mailing list -- time-nuts at febo.com
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