Studio Diary #16: Noise … From The Thunderbolt Cable?!?

I’ve been working on some recording today, and I ran into a problem that I never expected in a million years. I’ve got an audio noise problem that goes away if I unplug the Thunderbolt cable from my Mac.

Audio Routing

Let me explain what’s cabled into what …

• The Universal Audio Apollo x6 is connected to the Mac via Thunderbolt 3.
• I’ve also got a Belkin hub connected to the Mac via a second Thunderbolt 3 cable.
• My audio speakers are connected to the Apollo x6.
• The Apollo x6 console is configured to route the audio from the line inputs to the output where my audio speakers are connected.

i.e., the audio is going into the Apollo x6, and should be going straight out of the Apollo x6 to my speakers. The audio I’m hearing shouldn’t be going through the Mac at all.

And yet … I can clearly hear electrical noise in the audio.

What’s Going On?

I don’t know for sure.

I’m assuming that something isn’t electrically isolated correctly. Somehow, there’s an electrical circuit being formed from the Belkin hub, across the chassis of the Mac, and up to the Apollo x6. Hrm. I guess that would have to be multiple somethings?

Fortunately, if I unplug the Thunderbolt cable from the Belkin hub, the electrical noise goes away.

This is a bit of a pain. The Mac doesn’t have a lot of ports, and not being able to use the hub limits us to:

• audio interface
• Mac power supply
• no more than two external hard drives

I keep all of my recording sessions on an external hard drive. That leaves me only one remaining port to run an external hard drive for external sample libraries. That’s a bit tight.