Sunday, June 02, 2024

Sending audio to two devices on macOS

This morning I saw that the (very active) Bendigo Amateur Radio and Electronics Club were transmitting RTTY on 7.035. When I'm not in the shack I often leave an AirSpy HF+ running connected to SDR++ in server mode. This means I can sit by the fire and tune around on HF.

To decode a digital mode audio must be fed to FlDigi. I use BlackHole for routing audio from one app to another but I wanted to hear the audio as well so needed a way to send audio from the SDR++ app to both my speakers and a loopback for FlDigi. 

The trick on macOS is in the Audio Midi Setup app. Create a new "Multi-Output Device" and set the outputs to both BlackHole and your normal audio output (I use headphones with speakers plugged in to them. 

The audio output in the SDR software is set to send to the Multi-Output Device.

FlDigi is set to get input audio from BlackHole.

The final result is audio I can hear but also decode in FlDigi. Here's a bit of the BAREC broadcast.

Thanks BAREC for running the digital broadcast. I think it's great to have some regular signals on the band that aren't just FT8.


BerrySkies said...

Thanks for post Peter. You could also look at Loopback by Rogue Amoeba. Awesome software for routing audio every which way and also creating virtual audio cables in macOS. Alan VK2ATW

Peter Marks said...

Thanks Alan,

Yes I did try Loopback from Rogue Amoeba. It has vastly more features but costs US$109. I had never played with the Audio Midi setup and it looks like a power tool that's just built-in to macOS.