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Re: Is time an illusion?

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On 2017-09-26 21:37, Eric Sosman wrote:
> On 9/25/2017 6:16 PM, Daniele Futtorovic wrote:
>> Also, if there is a drift, can I expect that drift to be constant? That
>> is, if I observe that box A ticks, say, 1% faster than box B over a
>> given interval of time, can I assume that it will do so for /any/ given
>> interval of time? I guess not, right?
> 
>     I can't think of any reason to expect constant drift.  The machines
> don't operate at constant temperature, nor at constant voltage, nor at
> constant age ...  In my (very brief) look at the NTP documentation I
> found a glossary of terms.  There's a word for the first derivative
> of a clock's tick rate; the protocol anticipates that the rate is not
> a constant.  There's even a word for the *second* derivative of the
> tick rate; not even the rate of change of rate is considered constant!

Makes sense once you accept the basic premise that a CPU doesn't "tick"
at a perfectly constant or perfectly known rate, but still, bloody hell.
Gives a whole new meaning to the idea that solar flares impact our lives. ;)

>     I'm somewhat curious about why you need such lock-step agreement.
> What are you trying to accomplish?  Why do you need to measure the
> same interval on two independent stopwatches?

I'm rendering audio over a network, in real-time, or as close to
real-time as I can get. It's not just a matter of "render as much of
this as you can, when you can"; I want to be able tightly to control the
rendering, as well as have accurate measurement of the resulting latency
-- possibly over multiple endpoints.

The upside is that I'm not constrained by absolute time; I just need
relative time. Also, the human ear is sufficiently forgiving that I can
afford to be a couple milliseconds off -- but not too many (I think).

Specialised equipment is out of the question for me, as the software is
intended for general consumption. But based on the feedback here, I've
incorporated clock synchronisation into my protocol, and it seems to
work well enough, at least at low latencies. It's still an open question
how well it will work when they get higher, but I'll burn that bridge
when I get there.

Thanks a lot for the assistance.

-- 
DF.

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Thread

Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-25 22:30 +0200
  Re: Is time an illusion? Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-09-25 18:02 -0400
    Re: Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-26 00:16 +0200
      Re: Is time an illusion? Jerry Stuckle <jstucklex@attglobal.net> - 2017-09-25 19:18 -0400
      Re: Is time an illusion? Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-09-26 15:37 -0400
        Re: Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-27 01:13 +0200
          Re: Is time an illusion? Jerry Stuckle <jstucklex@attglobal.net> - 2017-09-26 21:00 -0400
            Re: Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-27 04:26 +0200
              Re: Is time an illusion? Jerry Stuckle <jstucklex@attglobal.net> - 2017-09-26 23:32 -0400
                Re: Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-28 10:58 +0200
                Re: Is time an illusion? Jerry Stuckle <jstucklex@attglobal.net> - 2017-09-28 12:50 -0400
            Re: Is time an illusion? Eric Douglas <e.d.programmer@gmail.com> - 2017-09-27 05:25 -0700
            Re: Is time an illusion? Arne Vajhøj <arne@vajhoej.dk> - 2017-09-30 22:57 -0400
  Re: Is time an illusion? Arne Vajhøj <arne@vajhoej.dk> - 2017-09-25 20:22 -0400
  Re: Is time an illusion? Marcel Mueller <news.5.maazl@spamgourmet.org> - 2017-09-26 20:18 +0200
    Re: Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-27 01:30 +0200
      Re: Is time an illusion? lewbloch@gmail.com - 2017-09-28 10:52 -0700
  Re: Is time an illusion? Eric Douglas <e.d.programmer@gmail.com> - 2017-09-26 12:59 -0700
    Re: Is time an illusion? Daniele Futtorovic <da.futt.news@laposte.net> - 2017-09-27 01:42 +0200
  Re: Is time an illusion? lewbloch@gmail.com - 2017-09-28 10:49 -0700
    Re: Is time an illusion? Robert Klemme <shortcutter@googlemail.com> - 2017-09-28 22:33 +0200

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