When using a USB sound card, you might encounter issues with Windows no longer being able to enter sleep mode automatically. It seems there are issues with what Windows seems to call a “Legacy Kernel Caller”, a system component that’s apparently needed for at least some of the USB sound cards. I’ve been specifically encountering these issues using a Sound Blaster Omni cards/module. The issues for me are also accentuated by using an otherwise great piece of software called Voicemeeter, basically a virtual soundboard. While without Voicemeeter, my system is still sometimes able to auto-sleep despite the Legacy Kernel Caller issues, using Voicemeeter, it is pretty much never able to auto-sleep anymore (but to be fair to Voicemeeter, it seems this happens even with other options of re-routing sound device output to another device, like when using the Windows Listen feature, so it’s not really a Voicemeeter-exclusive issue). This is possibly because it somehow keeps the sound card “active” – I’ve noticed that the Legacy Kernel Caller power request block goes away at times while using the sound card on its own, it never goes away while using Voicemeeter. Why that is I can not tell you (but as far as Voicemeeter is concerned, it seems to do this with other sound cards as well, it’s just that you can whitelist them, unlike the Legacy Kernel Caller). But what I can tell you is that the system is still definitely able to enter sleep mode normally if activated manually, it’s just that the timer for entering it automatically seems to never start, so the system just stays on all the time.
Thankfully, there seems to be a kind of workaround for this, and it took me a while to find (in fact I’ve combined several separate partial solutions into one), so I though I might share it with whoever finds it useful. I can tell you there’s quite a few people asking about a solution to exactly this issue with the Legacy Kernel Caller system component.
