Applies to Scarlett 4th Gen
Scarlett Solo & 2i2
Both the Scarlett Solo 4th Gen and 2i2 4th Gen have a stereo loopback channel. However, this works slightly differently from other devices with loopback as both of these units only have a stereo pair of outputs (Output Left & Output Right)
Using Loopback, you can capture your computer's audio and record it into your recording software on a separate channel alongside your mics or instruments. By default, Loopback on Solo and 2i2 only capture Playback 1-2 (your computer's output) if you want to send your analogue inputs signal into the loopback audio go to Focusrite Control 2 > Preferences and then enable: Send Direct Monitor Mix to Loopback.
Then anything you have set in your Direct Monitoring Mix in Focusrite Control 2 will also be sent out to the Loopback channels.
To use Loopback, select inputs channels 3-4 in your recording software and then mute the loopback channel in your recording software or change the channel's output to none, to avoid causing a feedback loop.
Loopback works by 'looping back' audio outputs from your computer to virtual input channels within your Scarlett. Any computer audio can be recorded into a DAW (Digital Audio Workstation).
With the 4i4, all routing for the Loopback channel is done in Focusrite Control 2, and you can create a custom mix for the Loopback. In the example below, we used Mix C and then zeroed the levels for the inputs and playback sources we wanted to have in the mix by using Option + Left Click (Mac) or Alt + Left Click (Windows)
When recording the loopback channels in your recording software, be sure to either set the output of the recording channel to none or to an output/playback channel that is not in your Focusrite Control 2 Loopback Mix. Otherwise, you will cause a feedback loop.
Selecting Loopback on Windows Applications
On Windows, when using software that is not recording software, the loopback channel will not appear, and you might only be able to select input 1+2 of the device. Please follow this article to expose the loopback channels as input, to then be able to select them in your Windows Application.
Selecting different I/O in non-ASIO Windows apps