As you think of putting your classes online amid the COVID-19 safety measures, you may be imagining that you’ll make videos or other media in which you talk into your computer microphone as well as play music into that same microphone. Maybe you are planning to play a recording over external speakers, which the microphone will then pick up and put back into your video—but this will distort the audio significantly. Or maybe you were hoping that the computer would just let you switch back and forth easily—ha, if only!

Instead, take some time to figure out how to get your computer to merge two separate audio inputs—your microphone, and your computer audio—into a single output, which would go into your video stream.

This is all from a Mac perspective, because that’s what I do, but the steps are certainly adaptable for PC.

What you need

Soundflower, a free app that lets you direct your audio output back into your input—in other words, to record the sound coming out of your computer into your computer, instead of playing it through the speakers.

LadioCast, a free app for combining audio inputs and outputs

Microphone to connect to your computer

Computer audio source, such as a recording or a virtual instrument played with MIDI

What you’ll do

Install Soundflower and LadioCast. There are detailed install instructions for Soundflower at that link—your computer might try to make this difficult for you, but just do exactly what the developer instructs. Set your computer audio output to Soundflower (64ch). You can do this by clicking on the volume bar or by going to your Sound settings in System Preferences (in the Output tab). Launch LadioCast and allow it to access your microphone. In the left column, for Input 1, use the dropdown menu to select Soundflower (64ch). Now is a good time to test that Soundflower is doing what it should—play some audio on your computer like you normally would, and you should see the horizontal monitor bars (labeled 1, 2, L, R) under Input 1 start bouncing up and down with the amplitude of the audio. Still working with Input 1, click the small buttons at the bottom to select both Main and Aux 1. They should appear in darker gray. In the left column, for Input 2, use the dropdown menu to select your microphone. Again, you should now be able to speak into the microphone and see the monitor bars reflecting your voice. Main should be the only small button at the bottom selected, by default. Don’t select other buttons. In the RIGHT column now, for Output 1, select Soundflower (2ch). This is going to send the combined audio from your inputs 1 and 2 back into your computer. For Aux Output 1, select your headphones. This is to monitor the audio that you are playing through your computer without also hearing your voice. Your settings now hopefully look like this. Finally, to send the combined audio streams to your video or video chat service, make sure to change your audio input (it may be called your Microphone) to Soundflower (2ch). Your students/participants will hear both your microphone and your audio source clearly.

How it works

Basically, instead of outputting your sound to your speakers, you output to Soundflower, which feeds the audio back into your computer as an input. So exactly the signal that you would hear coming out of your speakers is the same signal that gets sent over the internet. This eliminates the distortion and loss of quality that would come from re-recording the audio from your speakers back into the microphone before sending it over the internet.

Normally when you make a video, you get to select one and only one input device. The default is to select your microphone. The app you’re using to make video almost certainly does not have an option to combine two audio inputs. But that’s what you need: an input for your microphone, and an input for your music. That’s where LadioCast comes in. LadioCast takes your two inputs and combines them into a single output stream, which you can then select as your video’s “microphone.”

You’re also normally restricted to only one output on your computer audio. This is normally your speakers/headphones, but instead you’ve rerouted your computer audio through Soundflower. But it’s hard to run the class if you can’t actually hear the audio yourself, of course! LadioCast again comes to the rescue, because in addition to handling multiple inputs, it can handle multiple outputs. LadioCast can output your mic+music combo to your video, while also outputting the music only to your headphones (bypassing your default setting of outputting to Soundflower).

This is probably easiest to understand graphically.