Comparing VIdeointerrupt and Phototransistor Method results

One might assume that if the video interrupt result for a game is 42ms, that the photo interrupt result would also be 42ms. This is not always born out in reality. Let's look at an example. 

Guilty Gear Strive on PS5 and XSX results via video interrupt are approximately 43ms of  input lag. So, we might expect that when we run the phototransistor test on the Inzone M3 that it would give ~45ms Read1, 51ms Read2 extrapolating to 43ms and 51ms at the top and the bottom assuming a 120hz display with 8ms screen draw time (Guilty Gear command icons used for phototransistor testing are at 22% and 96% of the way down the screen, so 25% and 100% for ease of calculations in this example.)

Conversely, if it were a 60hz monitor, we might expect 47ms Read1, 59ms Read2 for 43ms and 59ms top and bottom by extrapolation, assuming 60hz with a screen draw time of ~16ms. 

 Let's look at the PS5 results on Inzone M3 first. 

This is not what we expected.  I've tested all the different variations of VRR and Hz, however they don't make a significant different here, so let's just focus on the top set of results. ~50ms at the top is about 8ms slower than what we were expecting. The screen does seem to be drawing out at 120hz (8.33ms, given ~6ms between Read1 and Read2, extrapolated to 8ms for the whole screen) however it doesn't start when we assumed it would.

Let's look at XSX results. 

This time it's closer to what we initially expected when the XSX outputs at 120hz. 43ms to 51ms is close to the 43ms to 51ms that we were expecting, allowing for a little bit of lag from the monitor. However, when we limit the XSX to 60hz, we get results similar to the PS5 of approximately 51-59ms.  

To give an analogy, let's assume you have an assignment due in two weeks. It seems that when you have a 60hz signal on the Inzone M3, the assignment is done wholely in the second week. Conversely, when you have a 120hz signal, the assignment is done in the first week.  With a 60hz monitor, we would expect it to start on the first day of week 1 and finish on the last day of week 2. 

Does this apply in the same way to all 120hz monitors? Not necessarily. I took the opportunity to run the same tests on the LGC2. Let's look at PS5. 

First thing to notice, when we have automatic and apply for the VRR settings, the results are fairly much the same as the Inzone M3. However, when we turn off the Apply to Unsupported Games option, the results change. Now it takes from 43-59ms, which is in keeping with what we expected from a 60hz signal on a 60hz monitor.  

Unfortunately I didn't test XSX on LGC2 at the time. I may go back later to have a look, however I would think it's unlikely to outperfrom the Inzone M3. 

Now, the above should apply to 60hz games. SF6 is an exception. It seems that Capcom really went the extra mile to get as much performance out of this game as possible. Let's look at the PS5 results. We can get the easy one out of the way first.

Street Fighter 6 with Input Delay Reduction off is very slow (~100ms). 

It's a bit faster on XSX, but still slow. Let's turn IDR on!

Almost half the input lag! And the other thing you will notice is that in this instance, Applying VRR to unsupported games does seem to come with an input lag reduction when 120hz mode is automatic. 

The results are similar for XSX, with an input lag reduction for VRR on (59-->55ms), and a massive input lag reduction going from 60hz to 120hz. (84-->54ms)

So in conclusion, unfortunately it's not a one size fits all approach to comparing video interrupt to photo transistor results. 

1. If you're playing SF6, turn everything on!

2. If the monitor is 60hz, expect the results for 60fps games to be fairly much equivalent between photo transistor and video interrupt.

3. If you're playing 60fps content for Xbox Series turn everything on

4. If you're playing 60fps content on PS5, it's likely that leaving VRR to Automatic but not Apply to unsupported games will give the best results across all monitors.