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Re: Is time an illusion?

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On 2017-09-27 05:32, Jerry Stuckle wrote:
> On 9/26/2017 10:26 PM, Daniele Futtorovic wrote:
>> On 2017-09-27 03:00, Jerry Stuckle wrote:
>>> If you're trying to synchronize audio with video, anything less
>>> than 100ms is generally considered sufficient and regular updates
>>> with ntp should work fine.  However, if you're trying to
>>> synchronize two different audio signals (i.e. left and right
>>> channels), you have to be less than around 50ms (1 cycle at 20
>>> Khz), which you won't get reliably without additional hardware.
>> 
>> I don't think I want to sync audio signals, but... what makes you
>> say I wouldn't get better than 50ms resolution?
>> 
> 
> Sorry, that should have been 50 microseconds, not 50 ms.  That's
> what you would need as a minimum to synchronize audio signals because
> the ear can easily hear phase differences between signals.
> 
>> Also, can you tell me how you arrive at the 20Khz figure?
>> 
> 
> It's generally considered about the minimum for synchronization for 
> non-high fidelity audio (i.e. voice and general sounds) - up to
> around 7 kHz or so.  The human ear can hear up to 15 kHz or so so you
> need something higher than that.  For high quality audio you're
> looking at around 45 kHz (3x maximum audible frequency).

Makes sense. Thanks a lot for the figures.

>> The way I see it, provided I get my clocks synched, the only other 
>> problem is the drift; otherwise I can do whatever I want. Therefore
>> if I find a workable time interval over the length of which drift
>> is negligible (say, <1ms), synchronisation is the only problem.
>> 
> It all depends on the computers themselves.  There is no way to 
> guarantee drift on its own will be < 1ms, and no internet-based 
> synchronization will keep them that close.
> 
> What is so important about keeping the time down to < 1ms?  You can
> have more variation than that even in must processing a signal due to
> the multiprocessing nature of the computers.

*Shrug* I'm just trying to be as accurate as I can afford to be. The
basic premise isn't signal mixing, but the transport of PCM audio at the
standard 44.1/48kHz sample rates. If I want flexibility with respects to
the lower end of sizes of the packets I divide the data in (which does
impact latency, which I want to minimize), I need to measure
sub-millisecond. If then the whole thing can also be used for signal
mixing over the network, all the better -- although from what you told
me, it doesn't sound like I'll be able to achieve that, at least not
without specialised clocks. But basically, for what it's worth, I'm just
trying to make something that'll be useful as possible.

For the record, I started this whole thing by using JACK
(<http://jackaudio.org>) with its net driver -- maybe you're familiar
with it -- but then found I had to roll my own, because NetJack only
uses UDP, and I want this to work over wireless, which turned out to be
a no-no. I've got both TCP and UDP going for now, and am planning an
SCTP
(<https://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocol>)
implementation as well.

-- 
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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