Mac USB audio output causes pop after stopping/pausing audio from local source

A bit of an update, and I hope a final nail in this issue's coffin:

I have been in contact with Topping about a completely different, and very complicated issue involving a hiss forming in the Right channel under very specific conditions (related to the very specific way I have things connected, the PEQ feature on the DAC, the sample rate set in the Audio MIDI app, and apparently the DAC's auto-sensing functionality). After some time, they were finally able to reproduce the issue on their end, and they sent me a beta FW to test out.

I have installed the FW, and while it fixes the problem they were presented with, it also fixes the popping issue I have posted here. This means I think I can now remove the D10s from the chain, and go straight from my Mac Mini to DAC/HPA via USB without any problems.

This is very good news, and I hope that they don't do anything to mess it up!

Topping is one of the many manufacturers of audio gear (DACs, headphone amps, small/desktop power amplifiers, etc...) based in China. Other similar companies are SMSL, Douk, Fosi, Gustard, etc...

I do not know why it double-posted, but I did edit the post with some bad news (for some reason, it re-posted the reply instead of just adding the edit). I spoke too soon, but I am now very certain on what causes the problem. It seems to be an issue with the data streaming to the DAC itself. The "pop" that is heard is essentially the XMOS USB Bridge on the DAC essentially going to sleep. If there is a constant stream of data being sent to the DAC, then it doesn't go to sleep, and therefore no popping will occur -- This is why connecting a USB DDC (Digital to Digital Converter) in between the Mac and DAC eliminates the popping since it bypasses the XMOS USB Bridge altogether. With some clever settings manipulation in the Audio MIDI app, I know that there is also a pop that happens as audio starts (i.e. pressing play on a music track, for example), so it happens when the XMOS USB bridge is woken up as well.

A clever person on Audio Science Review found a "solution" by booting the Qobuz app, and letting it run in the background. Because it sends a constant stream of data to the DAC, this also eliminates the popping.

None of this is a problem for Windows users because they have access to the XMOS audio control panel with the drivers, which has an option to change the DAC streaming from "on when needed" to "always on." With no such drivers for Mac users, and the default setting being "on when needed", the above two methods are the only known ways to prevent the popping from happening. Neither of these things are ideal (and should be completely unnecessary, IMO), so something needs to be tweaked somewhere. The fact that you can change the setting on Windows tells me that a software solution is possible, but how that is implemented for Mac users is the big question mark. If there's even something that can be done in Terminal to set something to have a constant stream of data sent to the DAC, I'd like to know.

I have been in contact with Topping about this, and the last thing they has said to me about this is: "Unlike Windows, MAC cannot achieve a continuous data stream by modifying the driver, so we may need to explore further solutions." That tells me they are at least interested in finding a solution.

I may also follow up with Apple Support because it could be something they can tweak in the back end with whatever kernel extension(?) is used to stream data to DACs.

One other tidbit of information I just discovered:

If I use the single ended headphone output on my DX5 II, there's no popping stopping/pausing audio from any source. A pop can still be heard using the single ended line out to my external amp/speakers from my Mac's local sources (Music app, and system notification sounds).

The form says to not expect them to respond, so I am not going to expect them to get back to me at all.

And I was mistaken in the FW fixing the issue. It did not. There was a change in the behaviour upon installing Tahoe 26.1 in that when playing music from local files or a web-based source, there's about a 5+ second delay before the popping occurs, and I think in my excitement I didn't wait long enough.

On 15.6.1 (the OS I was on when I initially posted this thread), the popping was within a second after pausing/stopping. Curiously, on Tahoe 26.1, when playing a system notification sound, the popping happens almost immediately after the sound has stopped.

It's one of those things where either Apple does something with the CoreAudio (kernel extension? system extension?) or the DAC companies do something in their device FWs to allow for the data/DAC streaming to be always on. Some clever people have done some things in Terminal to have a silent mp3 file constantly playing to prevent the XMOS USB bridge from going to sleep, but I honestly don't know if I really want to screw around with doing things in Terminal that could potentially wreck something. So far, the only "legit" way to do it is by running the Qobuz app in the background, and even that's silly to me. I want an official solution, not some DIY workaround.

A bit of an update, and I hope a final nail in this issue's coffin:

I have been in contact with Topping about a completely different, and very complicated issue involving a hiss forming in the Right channel under very specific conditions (related to the very specific way I have things connected, the PEQ feature on the DAC, the sample rate set in the Audio MIDI app, and apparently the DAC's auto-sensing functionality). After some time, they were finally able to reproduce the issue on their end, and they sent me a beta FW to test out.

I have installed the FW, and while it fixes the problem they were presented with, it also fixes the popping issue I have posted here. This means I think I can now remove the D10s from the chain, and go straight from my Mac Mini to DAC/HPA via USB without any problems.

This is very good news, and I hope that they don't do anything to mess it up!

EDIT:

Never mind, I may have spoken too soon. The popping returned, and I have no idea why. It was completely gone for some time, though.

Songs on my Music app are from purchased/downloaded files on the computer, so it is not streaming. I have used different power adapters already (it's something I've been trying to sort out for the last 8 months, and have exhausted just about every test condition I can think of). Plus, it happens on my Macbook Air M2, whether it's plugged into the wall or running off of the battery, even with a DAC that doesn't require an external power source (the Topping D50 III I have used can be powered via its USB input without the need for an external power adapter).

And I think you might have misunderstood? By "DDC", I mean Digital to Digital Converter, not Digital Direct Control. And the popping goes away when the DDC is in the connection chain because it galvanically isolates my DAC/HPA (DX5 II) from the Mac. The D10s I am using is simply acting as a bridge, passing the digital signal through to my DAC via TOSLINK:

I can also connect my Mac to the DX5 II via Bluetooth, and the popping goes away in that scenario, too.

The Mac has been restarted countless times, and the issue persists. I will try to run that code in Terminal, and see what happens. If I'm being honest, I am skeptical that that will work (and if it does, for how long?), but stranger things have happened.

Thanks for taking the time to respond!

Edit: running that code in Terminal did not eliminate the popping.

And a quick follow-up: I have contacted Apple Support.