Physical audio devices usually have two or more channels, each of which can carry distinct audio. For example, a stereo microphone has both left and right channels, while more complex mixers may have 8, 16, or even more channels. Loopback's virtual audio devices start as 2 channel stereo devices, but they can be configured to have up to 64 channels.

Loopback handles some channel mapping automatically. When you add a source or monitor to a virtual device, its channels will be mapped one-to-one with the device's existing output channels, as possible. Similarly, when additional output channels are added, the Pass-Thru source is updated and auto-mapped to them. Note that mappings for application and audio device sources, as well as monitors, are not automatically modified when output channels are added.

Manually Adjusting the Channel Mapping

Below, you'll see the automatic channel mapping for our device with iTunes and a USB microphone (for clarity, the Pass-Thru source has been removed). This automatic mapping will often be sufficient, but it's also possible to manually configure the virtual audio device's channel mapping, via the Output Channels column.

A default channel mapping

Adding Output Channels

As mentioned above, virtual audio devices initially have two channels. Using the (+) button next to the Output Channels column header, you can add channel pairs, up to a total of 64 channels.

A second pair of outputs has been added, but nothing maps to it yet.

Re-Wiring Audio Flow

Once your device has the desired number of channels, you can use the intuitive wiring system to configure your audio routing exactly as desired. To add a connection, click and drag from one wiring socket to another. As shown below, a wire will be drawn to visually demonstrate that a connection has been established.

Channel wiring, in action

Below, you can see that channels from iTunes and the USB mic have been manually mapped to four output channels.

A fully configured channel mapping

In this setup, audio from the physical microphone's audio will be heard on channels 1 & 2, while iTunes audio will be heard on channels 3 and 4. Custom setups like this make it easy to record audio to distinct tracks, just based on the channels selected in your recording application.

Removing Output Channels or Wiring

To remove a channel pair from your virtual device, click on it in the editor to highlight it, then click the Delete button in the bottom bar or select Delete from the Edit menu.

Removing a connection between a source and an output channel, or between output channel and a monitor, is performed in similar fashion. Click the wire you wish to remove to highlight it, then click the Delete button in the bottom bar or select Delete from the Edit menu.

Monitors

Loopback devices can also be configured to include monitors, allowing you to use a secondary audio device to hear how your virtual device will sound. For details see the Monitors page.

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