[LAD] Audio over net - an observation

Len Ovens len at ovenwerks.net
Sun Sep 28 15:52:10 UTC 2014

Focusrite's RedNet series of interfaces uses Dante as the transport 
protocol. Going to the Dante home page I find that an audio driver 
(mac/win) is available for $30 or so (there is apparently a linux version 
available from another party). Yet Focusrite sells a RedNet PCIe 
card for around $800... one hopes it has more on it than an ethernet port 
:)  That looks like a sound card to the computer. This card does not look 
like it has a special plug on it (like the locking ones some of the 
snake/mixing boxes have). I am wondering what other processing might be 
happening on this card to make it worth Focusrite's effort to produce. 
Routing to be sure, but the Interface boxes all have that anyway. DSP? 
Effects? maybe, but not useful on a Linux box I am sure.

I realize a big part of the cost is scale (lack of scale in this case), 
but can't help but think that the money would be better spent on a better 
mother board. For example moving from an i5/7 to a Xeon based board.

Reading more about the RedNet PCIe card. It is 4 lane, but the recomend 
installing in an 8 lane slot. They also recomend using a GB switch to 
which both the PCIe audio card as well as the MB native Ethernet port is 
connected. They are suggesting that all the audio will go through PCIe AI 
card and that control will go through the native enet port. This all may 
be to do with 128 channels at 192khz at 3ms. The native enet port has the 
dante driver on it too.

I am not suggesting that the Linux world embrace Dante as a protocol so 
much as learning from its implementation. I am not sure that building for 
192k is the way to go though.

Some numbers... if they are talking 192k with a 32sample buffer (like jack 
with 16/2?) it would seem there is a lot of extra latency built in as at 
48k and 16/2 the raw latency from card to jack is only .6ms and at 192k it 
would be less than .2ms... .3ish for return trip. So the network and ADC 
together take a lot longer. Considering my USB IF at 48k has an ADC time 
of ~.5ms, most of that is network.

I am looking forward to testing Fons' n2jbridge jack backend. I will not 
be using 192k however. I generally use 48k, but may try 96k to test 
differences in latency. My own low level protocol is way down the road, if 
it ever happens.

Len Ovens

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