Call audio update: Audio Hijack

With Audio Hijack 4, Rouge Amoeba added the ability to manually edit connections. I’ve been an occasional Audio Hijack user since 2004^[1], but I knew right away that this had the potential to bring it into daily use.

As I wrote a couple years ago, I had been using a DAW, Reaper, to route and process my everyday call audio, but that seemed heavy, and definitely not what it was designed for.

Instead of Reaper, I set up Audio Hijack. As with before, I’m using BlackHole to create two virtual audio devices: a 2-channel device I use as the call app’s mic, and a 16-channel device I use as the call app’s speaker. Then, Audio Hijack looks like this:

It looks like a lot, but talking through it from top to bottom, left to right:

• Call audio comes into the block labeled “Call far side” from the device called BlackHole 16ch because the call app is using it as its speaker.
• Far side audio runs through a volume control (that I pretty much always keep at 100%), then directly on to my USB audio interface so I can hear it (the block labeled Monitoring)
• My actual, physical microphone is plugged into my USB interface’s input, which shows up here as the input block labeled Mic.
• The mic is a mono device on input 1 the USB interface, so there’s a Channels block to duplicate input 1 so it comes out on both channels.
• As part of proper gain staging, I want to make sure that the gain knob of the interface is set correctly, so I stuck in a PFL meter block. I leave plenty of headroom and compress it later (more on that below), but want to make sure it’s high enough, too.
• Then there are several blocks Audio Units plugins to process my mic audio:
  • First up is AUHipass (labeled HPF), which I use to get rid of low-frequency energy that’s really just rumble and other noise. I set it to roll off below about 50 Hz.
  • For reasons I haven’t figured out, I sometimes have hum in my signal, so I keep RX 8 De-hum around. I don’t love how it sounds, though, so unless the hum is particularly bad, I usually keep it off.
  • The RX 8 Voice De-noiser is pretty magical. HVAC noise? Outside noise? Nah. I turn on adaptive mode and leave the rest set to the defaults.
  • The final block of the processing chain in a compressor. I use MCompressor because it’s free. The exact settings depend on mic placement (sometimes I have the mic in the frame of my video because it sounds better, but sometimes I move it out of the frame because it looks nicer), so I have to adjust the threshold. I usually stick to a 4:1 ratio and turn on make-up gain (“Maximize to 0 dB”). Because of that latter setting, I also turn on the limiter.
• Speaking of levels, next up is the AFL meter block. It should hopefully be hotter than the input meter, and more even. Still not clipping, though.
• Next I have a couple of switches:
  • The one labeled “Self 🎧” toggles whether or not I want to hear myself in my headphones. (Usually I do, but that’s just personal preference.) When it’s on, it allows audio to travel from the mic processing chain on to the Monitoring block.
  • The one labeled “Mute 🎙️” toggles whether my mic is sent on to the call, which is the BlackHole 2ch output device.

That’s it for mic routing, but there’s one more thing in the Audio Hijack session. Sharing application audio with a call can be tricky and unreliable (“Can y’all hear this?”), so I keep a block around that I can turn on to capture application audio and send it to both my ears and the call. If I can hear it, they can hear it. Plus, I didn’t have to un-share and re-share my screen to make it happen.

One other thing I’ve started doing is using a global shortcut to mute myself. Usually when I’m talking in a meeting, the call app isn’t in the foreground, and I like to be able to quickly toggle it because (let’s be honest), with a mic in my face, I worry about mouth sounds. (Unless you enable Original Sound in Zoom or a similar feature in other apps, this probably isn’t a huge concern, but still….)

There are a gazillion of these little apps out there. They all seem just a little scammy. I’d like to use Mic Drop, but it doesn’t support muting only a single device at a time. I ultimately settled on MuteKey. It’s not perfect: I need to quit and relaunch it after the computer sleeps and/or it’s unplugged from the selected device, and sometimes after quitting while muted it turns down the input level, so I need to use SoundSource or Audio MIDI Setup to turn it back up. But it gets the job done. I use the shortcut ⌃⇧Space because I can easily use it one handed with either hand — very handy for pointing with a mouse while talking on a call.

One of the reasons I like being able to hear myself in my headphones is that when the USB interface is muted with this app, I can’t hear myself either. So if I can’t hear myself, neither can the call, and if I can hear myself, the call can hear me, too.

So there’s the latest on my call audio setup. Let me know if you have any questions or suggestions on how to sound even better!