I haven't found out a whole lot about CobraNet yet. It seems very smoke and mirrorsish. I doubt we can beat intels phy/mac interface though. And it does have priority queues built into it. Maybe there is some way we can for some sort of time division multiplexing in the network that won't break everything else connected to it.
On 4/8/06, Ray Heasman <[EMAIL PROTECTED]> wrote:
I am an audio engineer, or was until very recently, anyway. I am
partially responsible for several of the 1394 audio reference designs
out there. I have also worked on PLLs for regenerating the clocks in
audio systems.
Ethernet is generally considered useless for pro audio unless you are
using CobraNet [1]. The standard Ethernet MAC is non-deterministic for
accessing the medium. This causes jitter in reconstructed clocks and
makes them useless. You can use CobraNet, if you don't mind paying
incredibly high licensing fees (in the region of $10/channel of audio
per device).
1394 has an incarnation that works over Ethernet cable - 1394b [2]. In
my experience 1394 provides reliable isochronous data transport, but
everything except the 1394 standard is screwed. The higher level
protocols were designed by people that didn't understand that 1394 is a
bus, not a network. Avoid it unless you do everything yourself. (The
MOTU devices are an example of not conforming to any of the 1394
standards. Good for them, because the standards suck). Furthermore,
unless you know what you are doing, it is unlikely that you will get
reliable hardware designed and built. Most 1394 chips are horribly
twitchy in subtle ways.
MOCA [3] looks promising. They implemented a standard the right way -
they made it work, then invited other people to make stuff using it.
Finally, if OGP decides to do an audio card of some sort, they need to
realise that generating and regenerating clocks is the most important
thing to do.
If you want to do pro audio, I recommend NONE of the above standards.
It's possible that MOCA could do what you need; I don't know. I do know
that 1394 requires fancy footwork to generate the kind of clock you need
for pro-audio. I also know that CobraNet is just too damned expensive,
and proprietary besides.
If you want to do good pro audio today on a linux machine, do yourself a
favour, and look at the sound card section at the RME web page [4], and
buy yourself something there. Their boards are already based on a Xilinx
FPGA, and OGP reinventing the wheel seems like a marginal idea to me.
Cheers,
Ray
1: http://www.cobranet.info/en/support/cobranet/
2: http://www.lecroy.com/tm/Solutions/SerialData/IEEE/default.asp?menuid=29
3: http://www.mocalliance.org/en/index.asp
4: http://www.rme-audio.de/english/index.htm
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