On Wed, 2012-01-25 at 09:43 +0000, James Courtier-Dutton wrote:
> My requirement is more of an experiment really.
> I would like to have ethernet connected speakers. (with a mini PC
> between ethernet and speaker)
>
> So, if you have two speakers that are separated, each being fed by the
> TCP/IP stream, can you get one mini PC to process the Left speaker
> sound, and the other mini PC to process the right speaker sound.
> Currently, to get the output of the two speakers synchronized, I would
> need each mini-PC to be well time synced together.
> I don't think NTP has the accuracy needed. The trouble is that sound
> moves quite quickly, so the accuracy of the samples being sent to the
> sound card has to be surprisingly good.
> If you expand the system to 7.1, the time sync problem is vital.
> So long as I can get the mini-PC system clock accurate, the inaccuracy
> of the sound card clock can be corrected.
> This same synchronization could make for much cheaper video walls etc.
> although bizarrely, timing of video is not so vital due to artifacts
> of perception.
I had been wondering whether the need was synchronising PCs with each
other, rather than with UTC.
IIRC you need something like 'better then 5ms' synchronisation for
sound, which probably should be feasible using between PCs on a LAN.
Jitter, of course, must be much lower, but the PCs crystal will be
plenty good enough for that.
There are some related existing technologies that might be of
interest...
by Ethernet:
http://www.cobranet.info/
or by radio:
http://www.ti.com/ww/en/analog/cc8520/index.shtml?DCMP=hpa_rf_cc8520&HQS=Other+OT+purepathwireless
http://uk.farnell.com/texas-instruments/cc85xxdk/kit-dev-wireless-purepath/dp/1854437
Last time I looked the TI solution was still point-to-point, with
point-to-multipoint still in the future.
If you're experimenting, you could also consider something like a simple
infra-red clock between PCs or from a central point to the PCs.
I'm not sure off hand whether ntpd slews the PC's clock or the both the
clock and the crystal oscillator. In the days when I was dial-up
connected, rather than broadband, I used to use Chrony, which definitely
slews the crystal, though it's raison d'etre is occasional-onluy
connection.
http://chrony.tuxfamily.org/
Gordon.
--
Gordon Scott www.gscott.co.uk
01256-476547
0794-1958207
--
Please post to: Hampshire@???
Web Interface:
https://mailman.lug.org.uk/mailman/listinfo/hampshire
LUG URL:
http://www.hantslug.org.uk
--------------------------------------------------------------
