Re: [LAU] open hw soundcard (was Re: status usb2 for sound)

On Wed, 11 Nov 2009 23:30:08 +0100 (CET)
karl@aspodata.se (Karl Hammar) wrote:

> Giso Grimm:
> > Maybe I am something missing, but what about the clock synchronisation?
>
> There are works to make ieee1588 (PTP) into linux, [1-4].
> That might help.
>
> In [5], they seem to get <10us offset from a master within 2minutes
> converging time. [6] gives a little different picture.
>
> > It would be nice to allow synchronisation of several devices via the
> > network connection. This transport medium typically has a lot of jitter
> > (even an unloaded gigabit system can be above 50µsec), however, the
> > jitter of typical AD/DA converters should be in the order of
> > nanoseconds.
>
> Do you (or anyone else) know the maximum allowable jitter useful for
> audio?

Jitter, as such is a solvable problem. You use a phase locked
loop with a long enough time constant (high division factor) to average
out the jitter. Where you have semi-permanent connections this time
constant can be quite long provided that all the slave oscillators are
pretty stable, and the master is rock solid.

An entire cycle of 48kHz is about 20 uS so jitter would have to be
significantly less than that to avoid 'cogging'.

-- 
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
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