Audio Issues when Using Apple’s USB-C Digital AV Multiport Adapter

MJ1K2I record podcasts and screencasts, and usually do my audio recording on my iMac, but recently I’ve been using my MacBook Pro (2017, sans touch bar) a bit. Since it only has two ports, and I needed to record something with my iPhone connected to it, I attached the dongle you see on the left: it has three ports, one is USB-C, one USB-A, and one HDMI. I bought this a few years ago to use with the crippled single-port MacBook, and while I don’t use it often, now that I have 100% more ports on my MacBook Pro, there are times I need it. The battery was running low, and I needed to connect a microphone via USB, so I used one port for the iPhone, and the other for the power and microphone.

I recorded about two minutes of audio for a screencast using Audio Hijack, and, as I always do, opened it in Rogue Amoeba’s Fission to check it and edit it. This is what I saw:

Audio artifacts

As you can see, there are some very nasty audio artifacts on the recording. Interesting, they only show on one channel, but they are very loud diginoise. I don’t know why this happens, but when I plugged the microphone directly into a USB-C > USB-A adapter, then into the MacBook Pro, the problem went away. Also, when the power cable wasn’t connected to the mammoth dongle, it worked fine. I can only assume that there’s something wrong with the larger dongle when it’s sending both power and data. I don’t think there’s any way to fix this, and I don’t really need to use this configuration often, but it’s worth noting if you do plan to do audio recording and need another peripheral connected to a Mac via one of these dongles.

Fortunately, I didn’t discover this after recording a podcast…