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Audio Dropouts with New (2018) Mac Mini [Solved -- Time Machine]
jdindc:
Thanks to everyone for their tips and suggestions. To respond to Brian's question, my dropouts are between 2 and 3 seconds. I have done a lot of experimenting in an effort to isolate the variables.
First, given prior experimenting and Brian's comment, I suspected that the problem might be related to either my USB cable or my USB DAC. So rather than connect my Mac Mini to my USB DAC (which is inside my integrated amp), I used a 3.5mm to 2-Male RCA Adapter Cable to connect the MM's headphone jack to an analog input on the amp. This meant that I was using the MM's internal DAC. I was still using MC to play the same music files. I played music this way for hours with no dropouts. (If it weren't for the drastically inferior sound quality of MM's internal DAC, I'd just keep this setup.)
Second, to eliminate MC as the cause of the problem, I played the same music files using my normal USB setup (MM's USB output to USB DAC), but I used iTunes instead of MC. The dropouts returned.
Taking the above two experiments together, I initially figured that the problem was either my USB cable or my USB DAC. I was going to buy a better quality USB cable to rule that as the cause out. Then, if that didn't work, I was going to see if the dropouts persisted with another USB DAC.
But then I saw DJLegba's post about audio glitches affecting 2018 Macs. The glitch is caused by Apple's T2 security chip, and it impacts some external USB 2.0 audio hardware. I am not sure if this glitch is what is causing my dropouts, but it certainly seems like it could be. I read everything I could find about the glitch on several forums. One workaround that seems to have worked for some people is to use a Thunderbolt 3 Dock (such as the CalDigit Thunderbolt 3 Mini Dock). I'm not exactly sure how the dock solves the problem. But I believe it bypasses Apple's internal USB, thereby bypassing the glitch.
I also read that Apple is aware of the problem and working on a fix. But I've learned not to hold my breath waiting for Apple fixes. But FWIW, the final post on one of the forums (posted 3/16/19) says that "the most recent macOS Mojave developer seed contains changes that improve the reliability of USB audio devices." So perhaps an OS fix is on the way and my problem will be solved. If this glitch is the cause of my dropouts, that is.
I know that it now seems likely that MC is not the cause of my dropouts. So I'm not sure how relevant my posts are to this forum. But I figured that it might be worth updating people on my situation in case they are experiencing similar audio glitches with their 2018 Macs.
I'd appreciate any thoughts/suggestions that people have. Thanks again to everyone.
Josh
blgentry:
Your results seem to strongly indicate that the "2018 T2 bug" is your issue. I never saw dropouts of the length you have. Nor was I able to get dropouts from other applications, despite really trying to force the issue by intentionally using TONS of RAM to try to provoke failure.
I'm very hopeful that an OSX update will fix this T2 issue.
Regarding the Thunderbolt dock: I'm guessing that this fixes the problem because the T2 chip is not used in Thunderbolt communications. I have a $65-ish box that plugs in to the Thunderbolt port on a Mac and provides one USB3 port and one eSATA port. It might also "fix the problem" since it is only on the Thunderbolt bus and not on the USB bus. Looks like it went up in price a bit:
https://www.amazon.com/Kanex-Thunderbolt-eSATA-plus-Adapter/dp/B00LOLBBQQ
Good luck to you.
Brian.
jdindc:
Thanks, Brian. I'm very hopeful that you're right and that the next OSX update will fix the problem. I'll report back as soon as I know.
Josh
jdindc:
I'm happy to report that it's been several days since I upgraded my 2018 Mac Mini to OS 10.14.4, and I've had no dropouts since. I'm relieved that the problem seems to be completely fixed. Thanks to everyone for their help.
Josh
Awesome Donkey:
Looking at the changelog for 10.14.4, it mentions this...
* Improves the reliability of USB audio devices when used with MacBook Air, MacBook Pro, and Mac mini models introduced in 2018.
There ya go, looks like they indeed fixed it. :)
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