Tuesday, February 19, 2019 [Tweets] [Favorites]

T2 Macs Have a Serious Audio Glitching Bug

Peter Kirn (via Hacker News):

The problem is, it appears that this new chip has introduced glitches on a wide variety of external audio hardware from across the pro audio industry, thanks to a bug in Apple’s software. Issues with the way the new chip synchronizes timing causes dropouts and glitches in the audio stream. (It seems basically all USB 2.0 audio interfaces will be impacted. This of course unfortunately leads users to blame their interface manufacturer, but the fault lies with Apple.)

Switching off “Set date and time automatically” in System Preferences will reduce, but not resolve the issue.


To clarify: all T2-based Macs, that is all Mac models from the 2018 generation, are evidently unusable with USB 2.0 audio interfaces, irrespective of vendor. Audio interfaces using FireWire or Thunderbolt are reportedly unaffected by this particular bug, but USB 2.0 is for the moment the most popular bus for audio devices, so nearly all owners of the new machines are encountering the issue.

Update (2019-02-20): See also: Stephen Hackett and Jason Snell.

Marco Arment:

I haven’t, but I’ve heard about it from enough people that it’s probably a significant issue.


I’m curious to know whether dropouts were occurring on older models when bandwidth heavy devices were in use - were the internal cameras on older macs connected over USB? Is that something anyone you know can try?


The problem is that USB was never a “real time” bus - usually, traffic on it can be kept to a minimum when you only have the built-in keyboard / mouse being the only consumers, and so the audio chips would get their way the vast majority of the time…

Stephen Nellis:

These reports are all the more interesting because, in the days of very powerful phones and tablets, one of the few really good reasons for buying a full-on laptop is processor-intensive work like pro audio.

Ricci Adams:

Note: switching off “Set... automatically” doesn’t eliminate the issue because timed appears to still sync on occasion, even when off. There are likely other issues at play too. Unloading timed entirely fixed it for me, but not everybody.

Update (2019-02-21): Ricci Adams:

Follow-up: The issue still occurs for me after running sudo pmset nopoll when timed is loaded. There may be different issues at play, however.

Also, in case it helps anybody else, the best way I’ve found to test is to rapidly check/uncheck “Set date and time automatically” during playback while searching Console for “pauseAudioEngine”. If the engine is pausing, you will glitch at some point.

Update (2019-02-22): See also: Accidental Tech Podcast.

Update (2019-02-26): See also: Joel Hruska.


Really got to disagree with this one. macOS has had glitches and dropouts with USB audio for years — well before the T2 showed up. I don't think my iMac Pro or 2018 MBP are any worse in this regard than my previous machines. As annoying as these issues are, they are *far* from "unusable" as the writer claims.

I've had USB audio glitches in macOS dating back to the 5K iMac and Sierra. I believe that people are seeing problems but am deeply skeptical that this is isolated to the T2, to USB-C, to cables, to Date/Time settings, or anything else. If anything, since I bought an iMac Pro and upgraded to Mojave my glitches have been less frequent.

Brutal. I was literally just about to buy a new Mac Mini and Focusrite USB interface this week to replace my last remaining Firewire-capable Mac. Seems I might have to re-evaluate, or at least be prepared to return the Mini.

I wonder if this will be resolvable by Apple via firmware update, or if the nature of the T2 will preclude it.

Maximilian Mackh

This is a core audio software glitch. Restarting it via the activity monitor fixes the issue for a while until it appears again randomly.

This is by design, not a bug. USB was never intended to be used to do realtime and isochrone work. It does not support clock synchronisation, and should never have been used to build audio devices in the first place (especially so call high end devices…)
That's the reason why FireWire was so popular for audio, and why real high end audio should use thunderbolt nowadays.

I don't think it's a directly related issue – other than macOS and USB audio not working – but for the entirety of El Capitan my USB-DAC was not working as it should. It worked just fine in Yosemite and earlier versions of OS X, but in El Capitan I started hearing hissing noise and had to unplug/re-plug it every day and I lost the ability to use my volume buttons. A lot of others had similar problems, as seen in multiple threads in Apple forums.

Some people argued it was by design, that you should not be able to adjust the volume by software but it was a regression for me. And then finally, when Sierra was release, Apple had fixed it, somehow. No more hissing noise ever and the software volume buttons worked again.

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