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Nesting one Loopback virtual device within another

Loopback’s virtual audio devices behave just like hardware audio devices connected to your Mac. That means it’s possible to use one Loopback device as an audio source inside another Loopback device. We refer to Loopback devices which are contained in others as “nested devices”.

You may be familiar with the MacOS feature of “Aggregate Devices”, which can be created in the “Audio MIDI Setup” app. Nested devices work similarly, but offer deeper functionality that is not built into MacOS, including controls for making multiple audio source assignments with distinct channel routing and monitor device options.

Creating a nested device

When you add a new source to a Loopback device (by clicking the (+) button at the top of the Sources column), you’ll be presented with a list of any existing Loopback devices in the Virtual Devices section.

When one Loopback device is added to the another, the nested device provides audio to the host device just as if it were a hardware microphone or other audio device.

Using nested devices as building blocks

Sending audio to multiple destinations

Creating a nested device may be useful when you’ve created one audio routing configuration for a set of apps and audio devices for use in one app, such as a DAW, and then you want to simultaneously send the same set of audio sources to a second destination using a different routing configuration.

For instance, in the example below, we’ve created a device named “To DAW” that gathers audio from the Mac’s built-in microphone and some app sources, and then routes that audio to a DAW using specific output channel pairings:

In this example, we also want to send the audio from these sources to our live streaming app for sharing online. However, our streaming app only accepts default stereo input, that is, audio on channels 1 & 2. That means the custom routing configuration created in our initial Loopback device, with six separate output channels, won’t work.

This is where a nested device comes in handy. It allows us to create a secondary routing of the same audio sources for use in a different configuration, without upsetting the routing of the original device. In other words, the same audio sources can get routed to two (or more) different places at the same time, with each device using its own custom routing configuration.

To accomplish the second routing configuration, we’ll create a second Loopback device named “To Live Stream”, and then add the first Loopback device (“To DAW”) as a Virtual Device audio source. The new “To Live Stream” device will aggregate all of the original audio into channels 1 and 2. Now, when the "To Live Stream" device is selected in our live streaming app, all source audio will be preserved and played on the stereo channels.

Routing audio from multiple microphones

This technique of nesting Loopback devices can also be useful when grabbing audio from multiple microphones simultaneously, such as when creating a local podcast recording. In this use case, much like our example above, a nested device can be used to collect multiple stereo channel input pairs from various speakers’ mics, and then send those sets of channels to a DAW for recording each speaker on a separate track. At the same time, a second Loopback device with the first device nested inside of it, can be used to “downmix” all of the separate speakers’ audio playing on multiple channels into a single stereo track that can be used in a screen recorder or VoIP call app.

Adding a secondary volume control

Nested devices are also useful for providing secondary volume controls, making it possible to adjust the combined volume level of multiple sources with a single master volume control within the Loopback app.