Microsoft released the KB4505903 update in July to resolve audio problems found with the Windows 10 May 2019 Update. TechPowerUp today reported that the problem wasn't actually fixed with the KB4505903 update, however, leaving some Windows 10 users with particularly vexing playback issues.
We say "particularly vexing" because TechPowerUp compared the issues to "Winamp circa 1999 running on a Pentium 133 with its CPU priority toggle set to 'low,' and the CPU being subject to the rigors of Internet Explorer rendering Yahoo.com over a 56K PCI soft-MODEM." You don't have to actually remember 1999 to guess that anything mentioned in the same breath as Winamp, Internet Explorer and a 56K PCI soft-MODEM isn't ideal.
The problem appears to stem from modifications Microsoft quietly made to the Deferred Procedure Call (DPC) tick-rate with the Windows 10 May 2019 Update. Those changes reportedly caused spikes in DPC latency--which leads to the audio stuttering and glitching issues TechPowerUp described--in systems featuring sound cards that don't support dynamic DPC. That support would have to be added to the devices by way of driver updates.
Most hardware isn't supported forever, though, because manufacturers can't be expected to release driver updates for products they sold years ago. That only becomes a problem when changes to Windows 10 make the operating system incompatible with these abandoned parts. It's a bit of an "if it ain't broke, don't fix it" scenario, except in this case annual updates to Windows 10 mean that Microsoft is continually looking to "fix" things.
The good news is that TechPowerUp reported that the issue's currently restricted to discrete sound cards. A combination of the KB4505903 cumulative update to Windows 10 and driver updates to devices that rely on the Realtek audio codec appear to have resolved the issue for most people. The bad news is that folks willing to buy a discrete sound card are the people who suffer the most when audio doesn't play back like it's supposed to.
We've reached out to Microsoft for more information and will update this post if the company responds.
In the meantime, if you have a discrete sound card and your audio playback reminds you of listening to a sketchy MP3 of "No Scrubs" downloaded from Kazaa, now you know why. One would hope that Microsoft's efforts to resolve the issue weren't restricted to the KB4505903 update's release in July; that'd be a bit of a scrub thing to do.