How to synchronise two Pro Tools rigs together

A step by step tutorial for synchronising Pro Tools on two Macs.

I've frequently found myself reaching the track count limit on Pro Tools, and other times I am pushing my iMac to its limit using many RAM hungry virtual instruments. Back in September 2010 I bought a Macbook Pro, which soon became my main computer for composing, because it was more powerful. So my iMac just stood on my desk collecting dust, which was a shame because even by today's standards it is still a powerful machine.

Wouldn't it be amazing if I could synchronise the transport players in Pro Tools on both of my Macs? Oh wait, I can! However when I tried to get it working I couldn't find a useful tutorial, so I spent several hours over a weekend fumbling in the dark trying to get it to work.

So if you have two Macs running Pro Tools and would like to synchronise them together you can read my step by step tutorial below.

But before we start, it is worth pointing out that there is another alternative, but this is a zero-cost solution if you already have the hardware and software setup. If you are a composer and wish to create fantastic orchestral pieces that require lots of RAM hungry orchestral samples but your computer can't run them all together without bouncing down to audio tracks, then you should look into Vienna Ensemble PRO. Vienna Ensemble PRO is a cross-platform mixing host that allows you to connect multiple computers together via Gigabit Ethernet connection. I'm not opting for this solution right now because I didn't want to spend money on new software, when I have all the hardware and software to link two Pro Tools rigs together.

The Theory

There are two things you need to know about synchronising digital audio devices together:

  1. MTC (MIDI Time Code) needs to be generated by a master machine and transmitted to the slave via a MIDI cable. The MTC will control the transport allowing you to control playback.
  2. When connecting two or more digital audio devices together you need to synchronise their sample rates by setting a clock source.

What you will need

  • Two computers running Pro Tools with their own individual licenses.
  • Two audio interfaces with MIDI in/out and S/PDIF in/out capabilities.
  • One MIDI cable.
  • Two coax S/PDIF cables.

Step 1

Decide which mac is going to be the master and generate the MTC, the second will become the slave and will receive the MTC.

Step 2

Using a MIDI cable connect the MIDI output on your master computer's audio interface then connect the other end to the MIDI input on the slave computer's audio interface. This will allow the master to transmit the MTC and the slave will receive it.

Step 3a

Connect one coax S/PDIF cable to the S/PDIF input on the master computer's audio interface, then connect the other end to the S/PDIF output on the slave computer's audio interface. This cable is used to send a stereo audio feed from the slave to the master Pro Tools session, this will allow you to monitor and control the balance in the master session. Connect the remaining coax S/PDIF cable to the S/PDIF output on the master and into the S/PDIF input on the slave. The function of this cable is to enable you to set a clock source to synchronise the sample rate of the slave audio interface to the master.

Step 3b

Your audio interfaces will have an application that allows you to adjust its settings. Open them up on both your computers, then on the master computer set the sync source to internal and set the sample rate (44.1 kHz or 48 kHz, which ever you work in). On the slave computer set the sync source to external - S/PDIF Coax. The application should automatically set the sample rate to match the master, it will probably give you a message to say it is 'locked'. If it doesn't do this it will say it is 'unlocked' and you will have to manually select the sample rate, obviously select the sample rate that matches your master audio interface.

Step 4a

On your master computer open up your applications folder and go into the utilities sub folder to find the Audio MIDI Setup tool (see Figure 1 below) and open it.

Figure 1 - Location of Audio MIDI Setup.

Locating of Audio MIDI Setup

Step 4b

Open the MIDI Studio window if it is hidden. To find it click the 'Window' drop down menu at the top of your screen then click 'Show MIDI Window'. In the MIDI Studio window you will see all the MIDI devices ever connected to your computer, including your audio interface. Click the Add Device button, then double click on this 'new external device' and rename it MTC. In the properties window check the boxes to enable the following:

  • Receives - MIDI Time Code
  • Features - MIDI Machine Control
Figure 2 - MTC Properties on master computer.

MTC Properties on master computer

Step 4c

In MIDI Studio window you need to connect the MIDI output of your audio interface (click and drag) to the MIDI input of the newly created MTC device (see Figure 3). The MTC external device we've created and setup is your slave computer's audio interface. Your master computer's audio interface is now capable of transmitting MIDI Time Code.

Figure 3 - Here is my master audio interface connected to the MTC.

Connected to MTC

Step 5a

On your slave computer open up the Audio MIDI Setup. Click the Add Device button, rename it MTC, and check the following properties:

  • Transmits - MIDI Time Code
  • Features - MIDI Machine Control
Figure 4 - MTC Properties on slave computer.

MTC Properties on slave computer

Step 5b

In MIDI Studio window connect the MIDI output of the newly created MTC to the MIDI input of your slave computer's audio interface. Your slave computer's audio interface is now capable of receiving MIDI Time Code.

Figure 5 - Here is my slave audio interface connected to the MTC.

Here is my slave audio interface connected to the MTC

Step 6

Open Pro Tools on your master computer and from the Setup drop down menu open the peripherals table. Select the Synchronization tab, then select 'MTC' for the MTC Generator Port.

Figure 6 - Synchronization settings for your master Pro Tools session.

Master peripherals

Step 7

Open Pro Tools on your slave computer and open the peripherals table. Select the Synchronization tab, then select 'MTC' for the MTC Reader Port.

Figure 7 - Synchronization settings for your slave Pro Tools session.

Slave peripherals

Step 8

On the slave computer's transport, select the 'Online' mode, shown in blue in Figure 8.

Figure 8 - Slave session is online and waiting for synchronization.

Slave session is online and waiting for synchronization

Step 9

On the master computer's transport, select the Generate MTC mode, shown in blue in Figure 9.

Figure 9 - Master session is ready to generate the MIDI Time Code.

Master session is ready to generate the MIDI Time Code

Step 10

Press play on the master computer's transport, then stand back and be amazed! Both Pro Tools rigs are playing simultaneously.

Step 11

Now that your two Pro Tools sessions are linked together you will need to remember to set the output of every channel on your slave Pro Tools session to the S/PDIF output. The S/PDIF output is usually the last stereo output, e.g. on my m-audio profire 2626 it is output 25 & 26. On the master Pro Tools session you will need to set up a stereo AUX track with the input set to the S/PDIF input. This will allow you to monitor the mix of both Pro Tools rigs together.

Step 12

Now that you've got both Pro Tools rigs playing together and you are monitoring the mix of both, you will probably have noticed that there is a slight delay between the two. Fear not, all you need to do is go to the session properties and offset the playback. This is fairly usually, it is just a bit of latency.

First you will need to work out the difference in time between the two sessions at a sample level. Open a click track on your master and set the output to the S/PDIF output, record of few bars of this click track into your slave session. Also on the master session record the output of the click track to an audio track, so you can see the waveforms (you can mute the MIDI click track now, you only need the waveform of it).

Now on the slave session route the recorded click track back to the master session, and record it to a second audio track on the master session. So now you will have two audio files shown in your master DAW; 1 the original, 2 the click sent to the slave and back. Now you can compare waveforms and see the delay, count the number of samples between the waveforms, this is how much you need to offset the playback of the master sessions, you can do this at the session preferences, by entering the number of samples as a negative value. Congratulations you are done.