For live shows I've put together a system built around 2 Macbook Pros, a master
and redundant safety.
Each mac runs about 140 virtual synths and drums within Logic
Pro 9 triggered by a master keyboard and Roland Td20 kit.
There's a little bit of
backing too.(The Logic enviroment is a thing to behold built by our fab keyboard player
with a little help from me.)
The hub of the system lives in a small rack containing a
Motu Midi Time Piece Av for midi routing and sync duties.
A Maudio Profire 610 audio
interface for the Master Laptop. A Maudio 410 for the Safety Laptop.
And finally a
Radial Pro D8 passive DI to connect to the outside world.
The great thing about the
radial is it's redundant inputs and although I lose about 7db of level through passive
mixing, the sound and signal to noise remain excellent.
The Master Mac is setup
to send MTC to the MTP which is set to Jam sync infinitely.
The Safety Mac externally
syncs to this newly generated timecode.
An MMC stop command from the master
thankfully halts the MTPs Infinite jam sync at the end of each song allowing it to sync a
fresh to the next number.
Now to acheive almost seemless take over of the master by
the safety in the event of a crash I send an audio control signal from the master into the
safety interfaces input.
Over all 7 Outputs (Backtrack,Drums,Synths,Drummers click)
on the Safety mac I placed an instantiation of Softube excellent Valley Dynamite plugin
working as duckers and keyed from the Masters audio control signal.
If the master
goes down, the control signal stops and opens the duckers on the safety which keeps
playing in sync from the MTP Jam synced MTC.
Frustratingly (one for Desmond here?) it
appears Logic Pro 9 Mutes any input at the moment the safety picks up sync from the MTP.
This causes the Duckers to open for a fraction of a second and for both the master and
safety to be heard FOH.
To get around this I created an additional audio control
track this time residing on the safety.This one is routed internally to Noise Gates over
all 7 safety outputs and also delayed by a 16th note such that when the safety picks up,
although the inputs are lost and the duckers open, the delayed safety control track
doesn't open the gates until the inputs are back online and the Master control signal can
shut the duckers.
Is this making any sense ?
I used to get crosstalk of the master control signal on main outputs but removed this
with the aid of an isolating 1:1 transformer between the master 610 output and the safety
Anyway the whole thing works really well except for one aspect and
here I must confess to being electronically challenged.
Both audio interfaces take
their power from the firewire ports of their respective macs and I assume their earth
The Radial is Passive.
When one of the macs is not powered I regain the 7db
loss of gain through the radials passive mixer.
This I think I understand as the
radial is a voltage divider.
However what baffles me is that in this situation I get
crosstalk across all odd and all even outputs of the Radial independantly (Could this be
crosstalk within the audio interface?).This is particularly annoying as the drummers click
is then potentially heard at FOH.
Now you might ask, what are the chances of one of
the Macs crashing in a way that all power is lost including the Battery power and thus
power to its audio interface?
Still it would be excellent if I understood why this is
happening and if there is a workaround so the show would hopefully never have to be
interupted for technical reasons.
I tried powering both interfaces with their own
power supplies incase this is some earth related issue.
Unfortunately regardless of
having independant power, they both appear to require power from the mac firewire busses
to fully function.
The Profire 610 has balanced jack outputs and the Firewire
410 has unbalanced outputs. The Radial has unbalanced jack inputs, main and redundant. I
use unbalanced TS jacks for all these connections.
Any advice and an
explanation on this mystery would be marvelously received