Re: [LAU] Audio over WIFI

On Mon, 19 Jan 2015, Leonardo Gabrielli wrote:

> Just to bring the discussion back to its original topic, I see and know already

Thankyou.

> that audio over 802.11 is always thought of as a geek thing when not an insanity,
> but at my institution we felt this as good challenge for engineering research and
> I've been working on that as part of my PhD studies in the last two years.
> Updates and material about the project are reported at our research group webpage
> http://a3lab.dii.univpm.it/research/wemust

I can see how wireless makes this possible.

> The project, called WeMUST, i.e. wireless music studio, was started to test
> current network technologies in a *studio*, but later we also addressed live
> stage usage and a concert was performed last summer on the sea. In that case we
> acquired signal with Debian-based ARM platforms (beagleboard xm) and sent it to
> special devices from Mikrotik through Ethernet. The Mikrotik devices have
> directional antennas and created 802.11a bridges from sea to land. The networking
> topology allowed for monitoring and the round-trip latency allowed by the system
> was 16ms at lowest (but could be reduced with a different HW choice). The
> musicians could synchronize well and all had the same latency, imposed by JACK,
> running on both the ARM and the PC mixing the signal on the land.

I was going to say 10ms is about where I start to feel disconnected from
what I am playing, but I realize I am thinking one way and round trip
would be about 20ms. So 16ms might be well workable.

I am probably just missing something, but I find it hard to think where I
would prefer wireless audio use in a studio where everything is close
enough for wire and generally there are no "stage acrobatics". Thought for
testing it makes great sense because it is easier to control the
environment. Also, hum and noise from guitar cables (for example) can be
proberly dealt with in a permanent studio in ways some stage setups can't
(one of my favourite reasons for wireless guitar is to remove the player
from all grounds to avoid buzz... my new bass doesn't seem to have this
problem though)

For stage use, this would be great. I can see a number of uses. Smaller
venues often require a snake to be run (analogue or digital) for people to
trip over, and with ends to wear out (aside from the cable itself...)
wireless would be nice and easy/quick to set up. Wireless already knows
how to deal with more than one channel at a time. One AP can deal with a
number of clients. (though the same tech could be used with analoge
wireless) The technology is bi-directional, a musicain could have one TX
pack for both audio and monitoring.

Directional antennas would make a huge difference. Also remember that most
802.11* transmitters are not running anywhere near maximum legal power
(this changes with antenna gain too). Ballancing gain, directionality and
erp might effectively remove a lot of background radio activity in the
band.

> To recap, my opinion is that 802.11 can be as good as any other wireless
> technology in providing music and compared to legacy analog techniques the
> quality is not compromised (unless the link is so bad that connection

The only concern I would have with personal radio packs, is ADC quality.
Resampling becomes manditory, of course, but may not be a real concern
(besides added latency). Compatability would be a question too, this is
where AES67 may help. Certainly with many mixers going digital i/o, adding
an AP to the net would make this stuff "easy"... if they all work
together.

--
Len Ovens
www.ovenwerks.net
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