How can I connect multiple PlayAUDIO12 interfaces together?

Introduction

The PlayAUDIO12 interface is capable of transmitting up to 12 individual audio tracks - but what if you need more outputs than that? If you are using a Mac OS computer the answer is that you can "stack" two or more PlayAUDIO12s together as a so-called "aggregate device". (Note: unfortunately this is not supported at the operating system level in Microsoft Windows).

Since Digital Audio Workstation applications can normally only access one interface device at a time, setting up an "aggregate device" is a way to create a "fake" virtual audio interface in the Mac Operating System that in reality is made up of two or more hardware interfaces. The DAW will think that it's just one big interface composed of virtual outputs, and then the Mac OS translates from those virtual outputs to the real hardware outputs. So when you create an aggregate device it is very important that the Mac OS understands correctly which hardware interface is which, and that they are all connected correctly. This becomes even more important when you are building a redundant failover system with two Macs and multiple PlayAUDIO12 interfaces connected to both of them.

The following procedure will show how to set up multiple PlayAUDIO12s combined into an aggregate device in a redundant failover setup with 2 Mac OS computers. Do take your time when setting it up and make sure you perform each step correctly for best operation.

Setting up your Aggregate Device

A common problem that you may run into when setting up two or more of the same type of interface is that if they are both connected at the start the names look exactly the same, and you cannot tell which interface is which. So the first thing to do is ensure that you have the same PA12 set as the primary interface and Clock Source on each computer. If you don't get this correct from the beginning you could end up with sounds coming out of the wrong outputs after a failover occurs, so it's important to get it right!

The most effective way to set up an aggregate device is to start with one interface and only add extra interfaces to the aggregate device after you complete setting up the previous interface.

Note: each step taken on computer A must be followed on computer B before moving to the next section.
  1. Start by connecting a USB cable from PA12(1) USB Port 1 to your first (primary/main/master) computer. We will refer to this computer as Computer A.
  2. Now connect a second USB cable from PA12(1) USB Port 2 to the second computer ( backup/slave). We will refer to this computer as Computer B.
  3. From the Mac OS Finder, choose Go > Utilities. Open the Audio MIDI Setup application.
  4. Go to Window and select Show Audio Devices:


     
  5. Click the Add (+) button on the bottom left corner in the Audio Devices window and choose Create Aggregate Device.


     
  6. You will see a new entry appear in the left column called Aggregate Device:


     
  7. With the new Aggregate Device selected, enable the checkbox labeled Use on the left side of the Audio Devices window to select the only PA12 in the list. 
Now you have created your virtual Aggregate Device, and added your first PA12 to it.

Aggregate Device Attributes

When setting up an aggregate device there are 4 important attributes to focus on:
  1. Sample Rate
  2. Bit Depth
  3. Clock Source
  4. Drift Correction
All 4 of these must be set up correctly on each computer in order to avoid issues.

For this first PA12 in the aggregate device we need to set these to the following settings on both Computer A and Computer B:
  1. Sample Rate should be whatever you have chosen for your backing track playback (in most case this will be 44.1 or 48) - set this in your Auracle or iConfig application. It must be the same for all interfaces you connect.
  2. Bit Depth will normally be 24 bit  - set this in your Auracle or iConfig application. It must be the same for all interfaces you connect.
  3. Clock Source - only one interface can be the Clock Source, and this will automatically be set to this first PA12 in the aggregate device. This means that this first PA12 will act as the Master Clock for all the other interfaces you add later.
  4. Drift Correction - since the first PA12 is the Clock Source, Drift Correction must be turned OFF in this case. Drift Correction will only be used for the interfaces you will add later.
If you are not sure how to set Sample Rate and Bit Depth on your interface, see this article. If you are using iConfig also make sure that the Clock Source in iConfig is set to Internal.

Don't forget to create these settings on both Computer A and Computer B!

This is Computer A:



This is Computer B:



 Now you have  successfully connected the first PlayAUDIO12 to the aggregate device. Congrats!

Connecting more PlayAUDIO12s

  1. Connect the second PA12 to both computers. USB Port 1 to computer A. USB Port 2 to computer B.
  2. With your Aggregate Device still selected in the left column, select the new PA12 in the Audio Devices pance and enable the checkbox labeled Use to add it to the aggregate device.
  3. Note that Drift Correction will be On automatically for this PA12. You must have this option On for every interface except the first one. This makes sure that all of the additional interfaces will correct any drift they have to keep their digital sample clocks correctly in sync with the first PA12. If they don't, you will get some horrible digital noises happening and you really don't want that!


 If you wish to add more interfaces to the aggregate device continue to add one at a time using the steps above.

Please note that although this procedure should work without problems in the vast majority of cases, because this aggregation takes place at the Operating System level it is beyond our direct control. Thus we cannot guarantee 100% compatibility in this aggregate mode.