[LAU] SPDIF plus NetJack for digital audio transfer between computers.

Brendan Furneaux brendan.furneaux at gmail.com
Thu Feb 26 13:55:08 UTC 2015

I play keyboard in a band, and use UbuntuStudio on a laptop for softsynths,
effects, and most importantly, MIDI routing (via mididings).  Across the
room is our studio computer, which runs Windows.  I am running audio out of
my laptop via a Presonus FirePod (aka FP10), which works fine.  The studio
computer has a Presonus FireStudio and Digimax, which are joined by an ADAT
lightpipe.  Both the FirePod and FireStudio have SPDIF ports. At the
moment, audio is traveling via audio cables from the hardware synths and
laptop across the room to the studio computer.  However, it seems like I
have everything in place to have a "simpler" setup, at least from a wiring
and D/A/D conversion standpoint, by using NetJack to send digital audio via
a crossover cable from my laptop to the studio computer.  The plan would be:

*The FireStudio (on the studio computer) must have its clock synced to the
Digimax via ADAT.
*The FirePod (laptop) can be synced via SPDIF to the FireStudio.  Thus, all
audio hardware will be on one master clock without any effort from the
*Use the FirePod to capture audio from the hardware synths.
*Use NetJack(1|2) to route audio from the laptop (both captured from the
hardware synths, and from softsynths) to the studio computer, via an
Ethernet crossover cable.

The last step is where I am running in to trouble.

For starters, NetJack(1|2) does not seem to be designed for the use case
where the sound cards on two networked computers are actually synced in
hardware; thus the normal operating mode where only the master can access
its audio hardware.  So far, my plan is to use NetJack2, with the laptop as
master and the studio computer as slave. I have thought of either using
audioadapter with the net backend on the slave, or of using netadapter with
the alsa backend. Both of these do resampling to compensate for drifting
clocks.  My first set of questions is: In the case that the clocks on the
master and slave hardware are already synced, do audioadapter and
netadapter still spend significant CPU time on resampling overhead?  Which
one is likely to be more reliable/less resource intensive? Can netadapter
receive MIDI? Is there some other software that would be better?

I currently have Jack 1.9.10 installed on both computers, and they work
fine individually.  They are configured with static IPs on the crossover
cable, and are at least able to ping each other.  However, I have not been
able to get NetJack2 to connect using either computer as the master.
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