Here at Pro Tools Expert we sometimes get an enquiry asking whether it would be a good idea for a user who needs increased IO to create an Aggregate Device in OS X. The response from the team is always along the lines of “do everything you can to avoid Aggregate IO devices as although it sounds like a great idea, in practice, they simply aren’t worth the trouble”. While there are occasional cases which justify their use, if there is an alternative, I’d always take it. 

What Is An Aggregate Audio Device?

An Aggregate Device lets you use audio inputs and outputs from different Core Audio devices at the same time with audio applications. With devices which support word clock, this can work well. With devices which don’t support word clock, there is an option called Drift, which accommodates un-synced clocking issues to some extent. Latency performance suffers when using Aggregate Devices and reliability can be erratic, and it is this reliability which is the reason why we try to dissuade people from using aggregated audio devices.

Mbox Compulsory

It seems a long time ago now but before Pro Tools 9 it wasn’t possible to use Pro Tools without Avid hardware. The demand for mobile systems was met by the Mbox line of interfaces and I still have a Mbox Micro in a drawer somewhere, at the time the only way to use Pro Tools with a laptop without having to lug a full-blown interface around!

With the introduction of Pro Tools 9, the change to supporting non-Avid hardware made it possible to use Pro Tools with ASIO or Core Audio hardware. MacBook Pro owners greeted this with great enthusiasm but because Core Audio sees the Built-In Input and Built-In Output as separate devices, and because unlike many DAWs, the Pro Tools playback engine doesn’t allow Pro Tools to address different devices for input and output, there was no simple way to address both the built-in input and output on a Mac.

Pro Tools Aggregate I/O

To address this, Pro Tools 9 automatically created a Pro Tools Aggregate I/O on any Mac it was installed on. This is an aggregate audio device made up of the built-in input and output to allow access to both at the same time.

This sounds like a sensible solution, so why would I suggest that Avid dispense with it?

The Pro Tools Aggregate I/O is, in my experience, unreliable and unnecessary because modern Macs only have a single 3.5mm audio jack which can be purposed as an input or and output the need for access to both is radically reduced. While the 15” Macbook Pro had input and output sockets up until the release of the Retina Macbook Pro in 2013, the last 13” Mac laptops to have both sockets were made in 2009!

Is There An Equivalent to Aggregate I/O On PC?

Our resident PC specialist Alan Sallabank says that "Windows doesn't have such a feature and to get such, you have to install Asio4All, which brings with it flakiness and the chance to drag the clocking off. Avid added the ability to use the WDM built-in devices with Pro Tools 12, but originally it wasn't compatible with Video tracks, plus I've never managed to get it to work properly. I do agree that PT needs better I/O management on both platforms."

Limitations Of The Playback Engine

Having the option of an aggregated Core Audio device wouldn’t be an issue if it weren’t for the fact that you have to have it and you have so little control over it. While I love Pro Tools, this is an area of frustration for me because the Pro Tools Aggregate I/O is compulsory - You can delete it but it will be automatically created the next time you boot Pro Tools.

To further frustrate me, there is no way to control the playback engines available in Pro Tools. Unlike, for example, the available networks on a Mac, which are addressed in order, down the list and the user can drag networks up and down the list. in Pro Tools, we have no direct control over which playback engine the system tried to use, if, for example, your interface is switched off and is unavailable.

Lastly, Pro Tools is unusual in that it doesn’t offer the option to set a device for input and for output separately. In a recent post, I detailed how to use a USB microphone with Pro Tools. The solution was to create an Aggregate I/O device because there is no output available on a microphone and Pro Tools doesn’t allow different settings for input and output. See below how, while Pro Tools has a combined setting for input and output, both Logic and Studio One (and many other DAWs) allow different devices to be set for input and output.

Do you use Pro Tools Aggregate I/O or do you do as I do and when editing on a laptop set the playback engine to use built-in output? Would you miss Aggregate I/O if it was an option rather than there by default? Leave a comment if you have something to share.