VO Weekly Workflow: Loopback I/O (Part 2)

Before we start trying to record different streams of audio, it’s helpful to understand a bit about I/O routing. As I mentioned in last week’s email, “I/O” stands for “Input/Output.” The actual I/O routing determines how each piece of software connects with different audio signals. Some signals – like that from the microphone – flow “into” the app, while anything that is broadcast from the app is flowing “out.” While this may seem like a simple concept, it can get a bit confusing when we start sending the output from one app to another.

If you’ve used Zoom, you’ve had to route audio into and out of that application. The “I/O” in Zoom sessions has become very user-friendly for consumer-level devices. Zoom prompts “Select a Microphone” and “Select a Speaker” when starting a session. Since most VO’s work with an audio interface attached to their computer, Zoom is actually sending all of the inputs from an interface into the Zoom session. If you have a two channel interface like a Scarlett 2i2 Gen4, Zoom will use the input from both of those sources. On the other hand, Source-Connect not only sees the Scarlett, but will require you to specify whether you want Channel 1, Channel 2, or even the Loopback Channels if they exist. This is a good example of how different applications manage the I/O differently.

Since I began talking last week about Loopback being used in Audacity, let’s start with that recording environment. And…let’s just say that the controls are a bit lacking. As of late 2025, the routing seems to be a holdover from the early days of this app. You can make these controls visible on the main Audacity window by going to the “VIEW” menu, moving through “Toolbars” and selecting “Device Toolbar.” This places small pull-down menus on the main screen. These show the current audio driver (Core Audio for MacOS), the Mic and Speakers selection, but most importantly the “1 – Mono”/”2 – Stereo” selection. These choices can also accessed through the Audacity Settings/Preferences, under the Audio Settings tab. If you have an interface with Loopback, “3” and “4” only show the number with no name for that input.

Audacity always routes the input sequentially. If you have only 1 track recording, that will always be capturing the audio coming from Channel 1 of the audio interface. If your mic is attached to Channel 2 of your interface (as with the new Gen4 Solo), then you will not capture any audio. In order to capture audio from Channel 2, you need a second mono track actively recording (or the “right” channel of a stereo track). Since Loopback audio shows up under Channels 3 and 4, there must be a corresponding track. You need to be recording into 4 mono tracks (or two stereo tracks).

Luckily, Audacity’s I/O routing is the most arcane. With Twisted Wave, when you go into Twisted Wave “Settings” panel, then the “Devices” tab, there will be a button for “Select Channels”. Here you can see all the inputs and Outputs properly named, and simply drag them into the desired order.

On multitrack music DAW’s, such as ProTools or Studio One, there will be some sort of a grid matrix where the Inputs and Outputs are designated once the audio interface has been selected. Adobe Audition is a bit of hybrid, as it has both a waveform (single-track) mode and a multitrack option. All individual inputs – both physical channels and the “virtual” loopback channels – are accessible when using multitrack.

It’s good to have an understanding of where these Inputs and Outputs are accessed in your software of choice. In the next post, we’ll look at how these can be used to separate and capture different parts of our session audio.

Have you tested your studio’s audio quality to make sure it meets professional standards? For a free review of your vocal recordings, please use the upload tool on my Audio Review page.

If you have found this resource helpful or inspiring, please feel free to share or link to this resource using one of the buttons below. If you would like to receive these weekly posts directly to your email, you can sign up here