Re: [LAD] 802.11n sound card

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To: <linux-audio-dev@...>
Date: Thursday, December 24, 2009 - 12:33 am

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Hi,

On Wednesday 23 December 2009 23:52:46 Patrick Shirkey wrote:

ll

No, the problem is one or two layers deeper in the stack. We are talking wi=
fi=20
here. No matter if there is only two devices on that network or a secure=20
connection, its still wireless transmission over radio frequencies in the 2=
GHz=20
range. Which is per se much more affected by any disturbance then a dedicat=
ed=20
cable is. Every mobile phone, every blue-tooth device, every neighbours=20
network, every iron in your ceiling will influence this. And not only with =
a=20
constant background-noise in your frequency range, but also with momentary=
=20
scrambling and such stuff. So in the layers you can not (easily) control by=
=20
software there is already lots of resending and rescheduling of packets. An=
d=20
all these introduce uncertainties and latencies you don't want in your audi=
o=20
transmission. Unless you can do with 100ms latency and more...

> Does anyone have an idea of how to work out the actual latency for a

The data-rate is not important. What is important is the struggle you do to=
=20
get a payload packet out and the reception acknowledged. Wifi is very versa=
tile=20
and allows usage (almost) everywhere. But you pay a high price in=20
predictability and latency.

Heck, even the wireless microphones struggle with problems and these "just"=
=20
send some analogue data. While digital is simpler in that its only zero or=
=20
one, its actually lots more complex on getting data out reliably.

> If we are talking about a studio setup with devices no further than 2

No, the bottle-neck is your neighbours accessing google and facebook via wi=
fi=20
disturbing your signal momentarily producing gaps and xruns. And the only w=
ay=20
around it is using an area where there are no neighbours.

Once the stream is stable and reliable, it will easily go below 20ms latenc=
y.=20
But getting the stream to be reliable is already complicated with things li=
ke=20
firewire (which has isochronous channels for exactly this purpose) and its =
more=20
complicated with usb (which has a master telling the clients when to send=20
bigger payloads to not disturb the other bus-members). Ask the jack-over-ud=
p=20
guys how difficult it is to create such stream reliably over tcp-ip network=
=2E And=20
they take lost packets into account (which means an xrun) and advise you to=
=20
use it on dedicated networks if you want more the the immediate experience.=
=2E.

If jacknet over wifi fills your needs, use it. But if it doesn't don't blam=
e it=20
on its developers, blame it on the underlying network (-technology) used.

Have fun,

Arnold

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Messages in current thread:
[LAD] 802.11n sound card, Patrick Shirkey, (Tue Dec 22, 9:05 pm)
Re: [LAD] 802.11n sound card, Jörn Nettingsmeier, (Tue Dec 22, 10:40 pm)
Re: [LAD] 802.11n sound card, Patrick Shirkey, (Wed Dec 23, 8:14 am)
Re: [LAD] 802.11n sound card, Arnold Krille, (Wed Dec 23, 9:10 am)
Re: [LAD] 802.11n sound card, Patrick Shirkey, (Wed Dec 23, 10:54 pm)
Re: [LAD] 802.11n sound card, Arnold Krille, (Thu Dec 24, 12:33 am)
Re: [LAD] 802.11n sound card, Patrick Shirkey, (Thu Dec 24, 12:49 am)
Re: [LAD] 802.11n sound card, Arnold Krille, (Thu Dec 24, 10:02 am)
Re: [LAD] 802.11n sound card, Paul Davis, (Wed Dec 23, 3:53 pm)
Re: [LAD] 802.11n sound card, Josh Lawrence, (Tue Dec 22, 10:43 pm)