Ball stutter -- finally caught it

[Gorgatron]

I have a ALP 4K and run VPX over OTG and have been seeing occasional ... something.  Lag, stutter, I wasn't quite sure.  Normally the ball rolls very smoothly, but sometimes it would kind of jerk around.  I would turn on the frame stats in VPX and it was always locked to 60 FPS, with the occasional blip to 59.  I couldn't see any difference in the stats between when it was working perfectly and when it seemed off.  

 

For hardware I have an Intel i7-12700KF and a RTX 2080TI running Win 11 driving a 4k/60 and two 1080p/60 displays -- it should be, and it is normally fully capable.

 

This evening while playing Flight 2000 using VPX 10.7.4:

 

 

I saw that it was being poorly and grabbed my phone to take a 240 fps video.  In the past when I have looked at the video (60 fps) I didn't really see anything out of the ordinary -- what looked bad when I was playing looked ok in the video.  This time I figured I would count the frames while the ball was rolling across the playfield.  It was roughly 4 frames per movement of the ball (as expected) and then it was 8 frames per movement for a little bit and then back to 4 frames.  So I think what I am seeing is that the ball movement drops to 30 fps from time to time.  It still moves at the same rate across the playfield, but it looks choppy.

 

I have the frame rate limiter set to 60 and if I turn that off the machine does about 250 fps while playing the same table, so I have plenty rendering power for this.  I have gone through all the posts I could find about performance and have tweaked settings to what I think are pretty low: all the AA / sharpening turned off (I don't think I need it on the 4k display), ambient occlusion off, anisotropic filtering on, and force full screen mode.  This doesn't happen all the time, not even most of the time.  As I said before, when it starts, it will be like this for a few minutes and then back to normal.  I have never seen a blip in the VPX performance stats or in Activity Monitor (when I have had that up).

 

Do other people see this?  Any ideas what might be or what I might try to debug/fix it?  Any tools I might use to get more info for an occasional blip like this?

 

Thanks!

 

[Gorgatron]

I was just thinking about Windows Defender and it last ran at 9:55 pm for 4 minutes.  My video is from 9:57 pm.  I think I might have a clue!  Now if I can tell it how to back off while I am playing...

[Gorgatron]

So that (defender) might be part of it, but I disabled it temporarily (that is all it allows) and I am still seeing this issue from time to time.

 

I wonder if others see this on systems that are otherwise set up and powerful enough?  Is that just the state of the system (OS, VPX, etc.)?

[Gorgatron]

Seen on reddit from WoodstockArcades:

Quote

I guess my only thought would be to ensure your tv and windows and vpx all show 60hz. Micro stutters are almost always caused by unmatched frame rates when you have overkill on the hardware end.

 

Sure enough, my dmd and backglass were at 30Hz -- not sure how that happened, but I have had a couple hours of play tonight with no stutter!

[Gorgatron]

Just a follow-up — the refresh rate was the last thing causing stutter. It is super smooth now all the time.