Re: [LAD] embedded high end audio

Fons Adriaensen wrote:
> On Fri, Aug 01, 2008 at 10:27:29AM +1200, Eliot Blennerhassett wrote:
>
>> Check these out:
>> http://www.cobranet.info - has a silicon implementation
>> http://www.axiaaudio.com/livewire/default.htm
>> http://www.ethersound.com/
>> http://www.audinate.com/
>
> Since you seem to be into this sort of thing: can cobranet
> be implemented in software, using standard network interfaces
> (assuming you have a realtime kernel, and the interfaces are
> dedicated to this task) ?

Livewire does have a software implementation (as a closed source driver).

AFAIK There is no cobranet software implementation,

But I don't see any technical reason why it couldn't be done. The packet
format is not published, but anyone with the publically available
information
http://www.cobranet.info/en/support/cobranet/developer/tech_data_sheet.html
and a packet sniffer and some cobranet nodes could figure it out.

Cobranet nodes all have software/hardware to allow them to sync to the
system master clock (the 750Hz 'beat' packet).
Having a PC play/record audio (e.g. from HDD) into a cobranet network
might not be difficult but if you wanted to also use the PC soundcard,
this is much more difficult unless you have a way to sync its sampleclock.

> I would be nice to have an open source standard for this
> sort of thing.

This may be of interest
http://www.ieee802.org/1/pages/avbridges.html

> Found it quite funny to read on Audinate's
> site that the problem with 'the others' is that they are
> closed and proprietary - Audinate isn't any better AFAICS.

The open standards they use are (at least) zeroconf, ieee1588 and RTP.
Its how they are put together...

As with all the others, a big part of the "secret sauce" is how the node
clocks are synchronised. The other part is how the audio routing is
set up, and the audio format negotiated between nodes.

http://www.proavmagazine.com/industry-news-print.asp?sectionID=1618&articleID=592312

Cobranet uses the beat packet and VCXO
audinate/Dante uses IEEE1588
Livewire and Ethersound I'm not sure of the exact mechanism.

To achieve low latency, some form of hardware assistance is probably
needed to regenerate the isochronous clock (in order to avoid samplerate
conversion/buffer adaptation schemes)

Finally, another overview paper http://nas.cim.mcgill.ca/wp.pdf

--
Eliot
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