Piping audio between applications: Configuring ham radio apps on Mac OS using SoundFlower (virtual audio cables)

You’re running some digital mode software like WSJT-X on your Mac. Normally you would use a physical audio cable between your radio to your Mac, either via a soundcard interface like a Rigblaster, or even a direct USB connection to your Mac and your radio. What happens though if you want to route your audio from one application to another? For example, can you pipe the audio from a Web SDR running in your browser straight into WSJT-X (or any other digital mode software)? What you need are ‘virtual audio cables’.

On Windows you have a product called VB-Cable (the approach for Windows is similar to what’s described here). On MacOS you have a couple of options. There’s a commercial product called Loopback from Rogue Amoeba, or an open source alternative called Soundflower.

Follow the instructions to download and install. Once installed, you’ll find a couple of extra sound devices in your System Preferences:

Think of the Soundflower device as your cable. Instead of configuring Speakers for output and Mic for input, if you configure the input for one app as Soundflower (one end of the virtual cable) and the output for another app also as Soundflower (the other end of the cable), and sound output from one app is now directed into input of the other.

Let’s give this a go to connect the output from a WebSDR with the input to WSJT-X.

First, from System Preferences, select the Output to be Soundflower (shown above).

Start up a browser and pick a Web SDR station from http://websdr.org/

Here’s KFS and we’re tuned in to 7.074Mhz USB to receive some FT8:

Next, start up WSJT-X and go to Preferences, Audio:

Note that with Input = Soundflower we’re routing the Output audio from the WebSDR running in the browser into the Soundflower virtual cable. From WSJT-X we’re then taking the audio from this virtual cable as the input into WSJT-X, effectively routing the audio from the web browser into WSJT-X.

Also note that with Output = Soundflower in WSJT-X, if we transmit on WSJT-X the audio will also go out on the virtual cable. With WebSDR we can’t obviously transmit, but if you have access to a remote rig like remotehamradio.com, you can route the audio from WSJT-X into the remote rig app. More on that coming next.

You might note that with this current configuration there’s no actual audio coming out of your speakers. With some virtual cables you have the option to monitor the audio passing over the virtual cable. On MacOS you also have the ability to create composite audio devices using the Audio MIDI Setup app:

This shows a ‘Multi-Output Device’ comprising both the regular built-in audio (your speakers) and Soundflower. Now you’ve got the best of both worlds. More on this next step, and also configuring to use remotehamradio.com with WSJT-X coming up next.

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