Using Multiple MOTU Traveler Interfaces for recording
Written by Andy Patterson
The Singing Wells Project is about to undertake its latest recording trip – to the Rift Valley of Kenya. The team will be travelling to more remote areas of Kenya to record the indigenous music of the area.
When we designed the mobile recording systems for the Singing Wells Project, we decided to go for the MOTU Traveler interface for a few reasons:
a) it has the option of BUS powering. – this worked out incredibly well when the power went out in Kisoro, Uganda, and didn’t come back on for around 12 hours..
b) sound quality and adaptability – it sounds good, has multiple sample rates available, and is robust.
On the first Singing Wells recording trip in March 2011, we recorded music in the coastal regions of Kenya. We were finding our feet, and so most recordings used no more than 4 microphones – and hence we used only the one interface (each of the two recording kits has one Traveler). Each Traveler interface has 4 mic pre-amps, 4 line inputs, and 2 optical digital ports.
So, when we came to the trip to Kisoro to record the Batwa, we had added a few extra microphones to the setup. We had a few extra Rode lavalier microphones, for picking up individual sources (vocals, instruments etc). Our first idea was to link the two interfaces by Firewire to create an aggregate device using the built in OS X aggregate device setup in the OS X Audio Midi Setup, however, the combination of this and ProTools 9 wasn’t a happy collaboration. Ordinarily we’d spend a bit of time trying to get this working – through downloading new software – latest drivers etc, but by now we were at the top of Ugandan mountain, so internet access wasn’t readily available..
By the next day, and after devouring the manual, we had developed a scheme, by which we’d use one of the interfaces as a MASTER interface. The other acted basically as a external mic-pre. Using the routing software, we set the second interface to send the signal from the 4 mic pres to its Line Outs, which we then connected up to the Line inputs of the Master interface with balanced Jack – Jack cables, which worked fine, although we used our whole supply of balanced jack cables.
So, for the next trip, we’ve purchased 2 ADAT optical cables. This will enable us to pass 8 channels of digital audio between the two interfaces. We only really need 4 channels for the 4 mic pres, but this is transferred digitally, rather than via the Jack to Jack cables, so as well as being less susceptible to interference from the outside world, it doesn’t use our full supply of Jack – jack cables.
You may ask – well why do we need 2 cables when we only need to send audio from the secondary interface to the Master interface? The reason for this, is that because we are using the digital connection, we need to make sure that both units are running at the same speed. This is called clocking and with the second cable we are sending a signal from the Master interface to the secondary interface. This signal is a reference, and tells the second interface what speed to run at. This ensures the signal it passes to the Master interface will be clean and not affected by cracks and pops.
So, how to connect the two interfaces up?
Connect your mics as usual – to the Master interface and to the secondary interface. Connect the firewire cable between the Master Interface and the Macbook Pro. You’ll need to power the second interface using the Wall wart style adapter (although you can power it by chaining the firewire between the two interfaces, but this isn’t recommended) You will need to connect the interface up to the firewire port to set up the routing, but while actually recording, you will be able to just power it from the mains.
Next, connect the ADAT optical cables. Use the A ports on each interface (the MOTU traveler has two ports – A and B). Connect the IN from the Master to the OUT of the secondary, and the OUT of the Master to the IN of the Secondary.
So, at this stage you will have your firewire interfaces connected to each other by FW400 and the Master connected to the computer with a FW400 – FW800 cable. When you switch on the computer (which already has the software installed), it will automatically bring up the MOTU audio setup window. This looks a bit like this:
Now, with having two interfaces connected up by firewire, there will be two tabs at the top which say Traveler MK3. One for each of the interfaces. For the MASTER interface you need to make sure the clock source is Internal. The Optical Input and Output for Bank A needs to be ADAT Optical. Clock source for this MASTER interface should be set to internal, as it is the MASTER clock source.
For the second interface, you need to make the Clock Source the Optical Input A. You also need to set the Optical Input and Output to be ADAT optical as above. At this point we are nearly ready to record, we just need to tell the interface to send the audio from the mic pres to the ADAT outputs.
For this we need the CUEMIX software, which should also be installed on the computer as well. Here are some instructions from the MOTU website:
In this example, an Traveler mk3 will be configured as a standalone A/D converter using its ADAT optical output by patching its analog inputs to its ADAT outputs:
- Connect the Traveler mk3 to the computer by FireWire, and turn on the interface.
- Open CueMix FX. Choose the Inputs tab, and then enable the Stereo button on the channel strips for analog inputs 1, 3, 5, and 7. (They will now appear as Analog 1-2, Analog 3-4, Analog 5-6, and Analog 7-8.)
- Choose the Mixes tab, and select Bus 1 in the mix bus menu.
- Set the mix bus output to ADAT A 1-2 by selecting the output pair in the bus output menu above the mix bus master fader. Set the master fader level to 0 dB.
- Mute all input channels except Analog 1-2. Set the Analog 1-2 fader to 0 dB. Set the balance control to 0.
- Select Bus 2 in the mix bus menu.
- Repeat the process with Bus 2 to route analog inputs 3-4 to ADAT A outputs 3-4. Then continue with Bus 3 (Analog 5-6 to ADAT A 5-6) and Bus 4 (Analog 7-8 to ADAT A 7-8).
- Open MOTU Audio Setup. Set the Traveler mk3’s sample rate and clock source appropriately.
- Wait about one minute for the new settings to be saved to the Traveler mk3’s internal memory, and then disconnect the FireWire cable from the back panel of the interface.
- Connect the Traveler mk3’s ADAT A output to the ADAT optical input of another device.
Hopefully this guide will help you to extend the possibilities of your recording setup with a second interface.