HDMI to VGA Converter Black Crush Solution

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Speedy
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HDMI to VGA Converter Black Crush Solution

Post by Speedy »

I decided to hook my Nintendo Switch up to my CRT about a month ago when I realized that playing 720p games on an 77" UHD TV wasn't the ideal experience. Step 1 was that I needed to find a way to accept HDMI. I started by using my Blackmagic SDI to HDMI adapter which looked great, but the fan noise on my BKM-42HD bothered me and I also preferred to have it run through all my automatic gscartsw switches.

I started looking around and saw a number of positive recommendations for the Tendak and Portta HDMI to VGA converters. I also looked on Amazon and Shmups saw favorable reviews for the Rankie converter as well. It seemed like between these affordable three converters that one of them would work well for my needs. They didn't...
Spoiler
The Tendak, Portta, and Rankie HDMI to VGA converters all have black crush issues and I'd guess that they all use similar chips because they all seem to crush near/below black in the exact same way. I eventually did some more digging on Shmups and JunkerHQ where I heard about the HDFury Nano GX which ultimately ended up being perfect.
I started with the Portta converter due to a recommendation from RetroRGB's converters page. I noticed that something was off as soon as I launched my first Switch game... shadow details were missing. The Switch doesn't have a good calibration test pattern for brightness, so I grabbed my Xbox One and used it's built-in brightness test pattern to check this converter and all the other converters I tested/tried.

I did some more research on Shmups and JunkerHQ and found that people seem to rave about the Tendak adapter. I ordered one up and had the same issue as the Portta wish crushing blacks/shadows.

I remembered also reading positive things about the Rankie converter on Shmups and also seeing great reviews on Amazon. I figured that I may as well give it a try for $8, but I had the exact same issues with missing information near/below black as the Portta & Tendak converters.

I have a Blackmagic HDMI to SDI adapter hooked up to the BKM-42HD SDI board on my BVM-D20 monitor so I decided to use that as a reference point. You can clearly see the top eye which represents "below black". Here's what that looked like:
Spoiler
Image
When looking at the Portta, Tendak, and Rankie converters you can't see the "below black" eye. They all looked the same, but here's a picture of what the Tendak looked like:
Spoiler
Image
I was pretty worn out at this point and thought that I wasn't going to be able to find a solution, but I then remembered reading a few posts about the HDFury Nano GX and also seeing it mentioned on the JunkerHQ page. It was expensive, but I decided to give it a try... and, it is just what I was looking for. Every test pattern I've thrown at it demonstrates it properly rendering above/below black and colors also appear accurate. Here's an image showing the same test pattern above that failed on the other converters:
Spoiler
Image
Has anyone else ran into this?
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Re: HDMI to VGA Converter Black Crush Solution

Post by gray117 »

:| Not sure...
Isn't that black eye supposed to be barely visible/invisible? ... Idk what the exact values are on that though but if anything looks too bright on hdfury? (I know its tough to tell on photo of screen).

I'd be slightly worried you're over-expecting black crush and might be doing yourself a disfavour, since that eye *seems* to be more evident than the MS advice?

Would also be curious what your baseline tv settings are - I'd start over.

For brightness/contrast specifically I like the kind of calibration images that have oppossing greyscale gradiants - the middle of both should be perfect grey (and in the middle of your screen) and obviously white/black at each extreme. Something like this if you can throw this up on your screen:
https://www.123rf.com/photo_9307532_mon ... scale.html
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Re: HDMI to VGA Converter Black Crush Solution

Post by ldeveraux »

When docked, the Switch supports 1080p output via HDMI. Don't know why that would look bad on your 77" display.
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Re: HDMI to VGA Converter Black Crush Solution

Post by nmalinoski »

Isn't black crush caused by a mismatch between full and limited color ranges? Is there a full/limited setting on the Switch that you could toggle?
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Re: HDMI to VGA Converter Black Crush Solution

Post by Fudoh »

HDMI to SDI is only a valid baseline if you can make sure that the input is what's expected by the BMD converter. I'm pretty that's supposed to by YCbCr, not RGB.

If you have the means, you should check what the HDMI to VGA converters actually expect. Do you get the IDENTICAL results when feeding YCbCr vs. full range RGB ?

And then Nintendo comes in with their bastard signal that is limited range RGB.

How did you interface the converters' output with your monitor's input ? Did you perform a sync conversion ? Or did you transcode to component ?

Below black isn't available when converting from VGA. The only exception would be a WRONG conversion from the initial YCbCr range to full range. But once that conversion is done properly the below black material gets lost anyway, since the 16 "zero point" in YCbCr is supposed to become 0 in RGB.
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Re: HDMI to VGA Converter Black Crush Solution

Post by Dochartaigh »

Speedy wrote:I was pretty worn out at this point and thought that I wasn't going to be able to find a solution, but I then remembered reading a few posts about the HDFury Nano GX and also seeing it mentioned on the JunkerHQ page. It was expensive, but I decided to give it a try... and, it is just what I was looking for. Every test pattern I've thrown at it demonstrates it properly rendering above/below black and colors also appear accurate.
How does the HDFury Nano GX compare to the HDFury 1 and 2?

The one thing I don't like about my HDFury2 is in 480p/720p it cuts off come of the image on the top and bottom and there's no adjustment for that (just L/R shift). Need to try my HDFury(1) and see if it does the same because it bugs me.
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Re: HDMI to VGA Converter Black Crush Solution

Post by strayan »

It would have been cheaper to buy a second hand 720p TV!
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Re: HDMI to VGA Converter Black Crush Solution

Post by orange808 »

The HDFury Nano GX has a knob to adjust the gamma. It's adjustable.
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Re: HDMI to VGA Converter Black Crush Solution

Post by Speedy »

gray117 wrote::| Not sure...
Isn't that black eye supposed to be barely visible/invisible? ... Idk what the exact values are on that though but if anything looks too bright on hdfury? (I know its tough to tell on photo of screen).

I'd be slightly worried you're over-expecting black crush and might be doing yourself a disfavour, since that eye *seems* to be more evident than the MS advice?

Would also be curious what your baseline tv settings are - I'd start over.

For brightness/contrast specifically I like the kind of calibration images that have oppossing greyscale gradiants - the middle of both should be perfect grey (and in the middle of your screen) and obviously white/black at each extreme. Something like this if you can throw this up on your screen:
https://www.123rf.com/photo_9307532_mon ... scale.html
Yes, the black eye is supposed to be invisible. I have the brightness turned all the way up on my monitor for testing and to illustrate the problem. You should always see the closed eye when turning the brightness up and then the closed eye should disappear once you turn the brightness down to reference level.
ldeveraux wrote:When docked, the Switch supports 1080p output via HDMI. Don't know why that would look bad on your 77" display.
It would be great if the Switch rendered games at actual 1080p, but most games are just output at 1080p but rendered/scaled from anywhere between 540p-900p. It seems like a majority of content hits 720p reguarly on Switch.
nmalinoski wrote:Isn't black crush caused by a mismatch between full and limited color ranges? Is there a full/limited setting on the Switch that you could toggle?
Black crush can be caused by a full/limited color range mismatch. I took all the above pictures with limited color range because the issue was substantially worse with full color range across all converters (Tendak, Portta, Rankie). The only adapter I didn't test full color range on was the HDFury.
Fudoh wrote:HDMI to SDI is only a valid baseline if you can make sure that the input is what's expected by the BMD converter. I'm pretty that's supposed to by YCbCr, not RGB.

If you have the means, you should check what the HDMI to VGA converters actually expect. Do you get the IDENTICAL results when feeding YCbCr vs. full range RGB ?

And then Nintendo comes in with their bastard signal that is limited range RGB.

How did you interface the converters' output with your monitor's input ? Did you perform a sync conversion ? Or did you transcode to component ?

Below black isn't available when converting from VGA. The only exception would be a WRONG conversion from the initial YCbCr range to full range. But once that conversion is done properly the below black material gets lost anyway, since the 16 "zero point" in YCbCr is supposed to become 0 in RGB.
My understanding of the BMD converter is that it supports both YUV & RGB. I tested YUV, RGB Limited, and RGB Full going into the BMD converter and it handled all of them nearly identically. I think it converts them all to YUV. Because of this, I used YUV across everything that supported it and if not, I used RGB limited.

I interfaced the HDMI to VGA converters' output with the BVM via an Extron RGB 203 Rxi. My understanding is that the Extron RGB shouldn't be doing any color space conversion but just sync combining. My understanding is that the Extron RGB just takes the format it receives YUV or RGB and passes it straight through.

With that said, I think the HDFury Nano GX is converting YUV (and even RGB Full) to RGB Limited and I think it always outputs RGB Limited. I think a BVM always expects RGB Limited, correct?
orange808 wrote:The HDFury Nano GX has a knob to adjust the gamma. It's adjustable.
Correct, but gamma is different from RGB range. With that said, the gamma adjustment is fun to use.
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Re: HDMI to VGA Converter Black Crush Solution

Post by Fudoh »

I think a BVM always expects RGB Limited, correct?
there's not really something like it in the analogue domain. Closest would be the 7.5 IRE pedestal found for the zero black level in some countries.
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Re: HDMI to VGA Converter Black Crush Solution

Post by fernan1234 »

When I'm using HDMI to VGA on my BVM, RGB full always looks better, but only slightly. The difference between full and limited on an analog monitor does not seem to be nearly as evident as on a digital display.

I do think think that the HDFury converters produce better results overall than the Tendak, but for most uses the difference will not be significant to justify the large price difference.

edit: I'm not sure what the Nano does, but the 3 (and 4 probably also) passes through whatever it gets, and it can also "color upscale" from limited to full with a dipswitch setting.
Last edited by fernan1234 on Wed Jul 03, 2019 8:27 pm, edited 1 time in total.
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Re: HDMI to VGA Converter Black Crush Solution

Post by Speedy »

Fudoh wrote:
I think a BVM always expects RGB Limited, correct?
there's not really something like it in the analogue domain. Closest would be the 7.5 IRE pedestal found for the zero black level in some countries.
Are you saying that BVMs would expect RGB Full, but would simultaneously expect 7.5 IRE to be "reference black"?
Or, are you saying that the HDF1 Nano GX must be outputting black represented at 0 IRE?
fernan1234 wrote:When I'm using HDMI to VGA on my BVM, RGB full always looks better, but only slightly. The difference between full and limited on an analog monitor does not seem to be nearly as evident as on a digital display.

I do think think that the HDFury converters produce better results overall than the Tendak, but for most uses the difference will not be significant to justify the large price difference.

edit: I'm not sure what the Nano does, but the 3 (and 4 probably also) passes through whatever it gets, and it can also "color upscale" from limited to full with a dipswitch setting.
Isn't crushing black an issue in any circumstance? Or, are you saying that its ok for an adapter like the Tendak to crush black as long as it is below reference black?
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Re: HDMI to VGA Converter Black Crush Solution

Post by Fudoh »

Are you saying that BVMs would expect RGB Full, but would simultaneously expect 7.5 IRE to be "reference black"?
Or, are you saying that the HDF1 Nano GX must be outputting black represented at 0 IRE?
IF the Nano is converting YUV or limited range RGB into an analogue signal with a pedestal (in order to avoid a range conversion in the first place), then you'd be supposed to calibrate that pedestal away on your display's end - readjusting the black level, so 16 becomes your "absolute black" point. And by all means we'd be talking a washed out image and not one with black crush.

(but to reiterate : losing BtB (blacker than black) parts of the signal is NOT black crush. It's common sense and supposed to happen)
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HDMI to VGA Converter Black Crush Solution

Post by Speedy »

Fudoh wrote:
Are you saying that BVMs would expect RGB Full, but would simultaneously expect 7.5 IRE to be "reference black"?
Or, are you saying that the HDF1 Nano GX must be outputting black represented at 0 IRE?
(but to reiterate : losing BtB (blacker than black) parts of the signal is NOT black crush. It's common sense and supposed to happen)
Isn't it preferential for the monitor (end of signal path) to calibrate BtB (blacker than black) to the display instead of the converter truncating it from the signal?

I always find it difficult to calibrate the correct brightness level (by eye at least) on a display if BtB is truncated.

Regardless of all that, to my eyes, it seems like the Tendak is also truncating near black and not just BtB.
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Re: HDMI to VGA Converter Black Crush Solution

Post by Fudoh »

Isn't it preferential for the monitor (end of signal path) to calibrate BtB (blacker than black) to the display instead of the converter truncating it from the signal?
from a practial point of view: doesn't matter. But technically RGB signals are just not meant to support BtB and WtW.
Regardless of all that, to my eyes, it seems like the Tendak is also truncating near black and not just BtB.
very well possible.
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Re: HDMI to VGA Converter Black Crush Solution

Post by Speedy »

I know this might seem unrelated...

Don't consoles like a SNES calibrate to the equivalent of RGB Limited?

I get that there is no such official format from what you're saying, but it seems from my testing like an NTSC SNES will output BtB which means that it should be calibrated to IRE 7.5 as reference black.

Given that most consoles output in RGB Limited, doesn't it make sense to just keep everything in that same colorspace if you're connecting everything to a single input on a NTSC CRT?

...I could be way off here though so please feel free to educate me ;)
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Re: HDMI to VGA Converter Black Crush Solution

Post by Shogun »

Apologies for digging up this old thread but I purchased the Portta unit and experienced the same issue described here. After lengthy troubleshooting I established the Portta was at fault for my contrast/brightness issues. I bought it because it had favorable reviews elsewhere claiming good picture quality and high pixel clock however neither of those are proving true. The other problem when it came to pixel clock was at higher refresh rates the unit exhibits these green color artifacts in dark areas when its being pushed too hard. Sure it gives you an image but there is green fringe everywhere. Stepping down the resolution and/or refresh rate resolves the issue.

My question is does anyone know of any converters that have good picture quality and can do a decent pixel clock? I don't need anything crazy. The Sunix and other variants get recommended a lot but none of them have been in stock for months. There are a bunch of new USB-C converters now that are recommended but my gpu doesn't have a usb-c port. I looked into buying a video over USB-C PCI card but it looks like the only company that makes these is again Sunix and it hasn't been in stock. I looked into HD Fury but they charge a hefty premium and have been pretty quiet as of late. You'd think they would have developed some new products or something. Does anyone have any recommendations for HDMI/DP to VGA converters?
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Re: HDMI to VGA Converter Black Crush Solution

Post by Hoagtech »

Lets dig this thread from the dead shall we?

I replaced my desktop monitor with a Sony CRT monitor recently and was appalled when I saw the Jitter and black crush that happened when I used the Office Max brand DAC on my PC.

I used the Tendak at home but it suffers the same black crush issue without the jitter.

The HD Fury Nano GX is now discontinued.

Where are we at for a reliable HDMI to DSUB these days?

Bonus question. I'm running an RTX 3070 Super with no VGA. Can I run another PCI card with VGA support and not lose my 3070 performance when hooked up to a VGA monitor?

If so. What's the cheap card people use for it?
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Re: HDMI to VGA Converter Black Crush Solution

Post by Guspaz »

Work has been done to evaluate a lot of them: https://www.retrorgb.com/hdmi-to-vga-dac-analysis.html
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Re: HDMI to VGA Converter Black Crush Solution

Post by Hoagtech »

Guspaz wrote: Tue Nov 21, 2023 11:07 pm Work has been done to evaluate a lot of them: https://www.retrorgb.com/hdmi-to-vga-dac-analysis.html
In this case I would prefer buy a more expensive recommendation than a cheaper one.

I bought one of the Amazon ones but I'm not getting my hopes up as they repackage different chips in China with the same brand name.

Before you go. What would you recommend for a PCI card to use with my PC tower?
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Re: HDMI to VGA Converter Black Crush Solution

Post by jd213 »

I'm perfectly happy with the Benfei cable (edit: which is currently only like $8 on Amazon), I somehow doubt I'd be able to tell a difference with a "better" DAC, although I admit my OCD is urging me to try a higher rated one....


I usually have a bit of black crush on some of my CRTs anyway, since they cause minor afterimages in my retinas if I don't turn down the brightness.
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Re: HDMI to VGA Converter Black Crush Solution

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Hoagtech wrote: Tue Nov 21, 2023 11:58 pm
Guspaz wrote: Tue Nov 21, 2023 11:07 pm Work has been done to evaluate a lot of them: https://www.retrorgb.com/hdmi-to-vga-dac-analysis.html
In this case I would prefer buy a more expensive recommendation than a cheaper one.

I bought one of the Amazon ones but I'm not getting my hopes up as they repackage different chips in China with the same brand name.

Before you go. What would you recommend for a PCI card to use with my PC tower?
I didn't do that work so I can't make any recommendations.

Using a secondary older GPU to output analog signals while getting the acceleration from a newer GPU works, Windows supports that, but the framebuffer copy does induce additional latency and a performance hit.
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Re: HDMI to VGA Converter Black Crush Solution

Post by Gunstar »

Check out Kuro Houou's list here: https://docs.google.com/spreadsheets/d/ ... edit#gid=0 (They should really start a thread here!)

Those IcyBox DACs are cheap and perform well. I bought three of them, the ICY BOX IB-AC516, IB-AC502, and the IB-AD502* (this apparently is the same as the AC502 but it also can be powered by USB. *Not on the spreadsheet):
Image
The AC516 model had a fair bit of ripple/jitter and it didn't perform well with an SLG in situ. The AD502 DAC from my little testing had minimal ripple from what I could see and was fine with an SLG.
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Re: HDMI to VGA Converter Black Crush Solution

Post by Gunstar »

Guspaz wrote: Wed Nov 22, 2023 1:26 am Using a secondary older GPU to output analog signals while getting the acceleration from a newer GPU works, Windows supports that, but the framebuffer copy does induce additional latency and a performance hit.
Interesting, do you know roughly how much latency there might be? I planned to do this with a CRT emu setup but maybe it's better if I just get the most powerful single card compat. with CRT emudriver
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Re: HDMI to VGA Converter Black Crush Solution

Post by Guspaz »

It adds half a frame of lag and costs you a bit of performance. The latency will depend on the refresh rate you use.
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Re: HDMI to VGA Converter Black Crush Solution

Post by orange808 »

Guspaz wrote: Thu Nov 23, 2023 10:44 pm It adds half a frame of lag and costs you a bit of performance. The latency will depend on the refresh rate you use.
Can you share a link on that? I didn't know there were any solid numbers. I understand what needs to be done, because the frame buffer isn't shared memory or available for direct manipulation. I just didn't know there was a standard latency that we could expect.
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Re: HDMI to VGA Converter Black Crush Solution

Post by Guspaz »

Here's a relatively recent example: https://jarrods.tech/laptop-latency-com ... s-optimus/

Keeping in mind that muxless Optimus (nVidia's marketing name for what is now a standard Windows feature but wasn't always) is the same thing as we're talking about here. In their case, they're getting 3ms of latency at 165Hz, which is half a frame at that refresh rate.

This is also a recent example and also testing at 165 Hz getting the same results, though using different tools: https://techteamgb.co.uk/2023/07/03/nvi ... explained/
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Re: HDMI to VGA Converter Black Crush Solution

Post by kitty666cats »

Taking the time to read through the link below & look at the comparison photos really hammers home the jump in quality you're gonna get from the higher rated DACs in the related spreadsheet. There's some BIG differences in color accuracy & black crush/shadow detail.

https://tinyurl.com/dacanalysis

The AG6200 chipset that's EXTREMELY common in HDMI to VGAs yields pretty damn shitty results. Kinda a shame, most people using HDMI to VGA DACs for 15kHz MiSTer direct video are settling for those ones just because a lot of people confirmed the copypasta configs working with them. I suppose ignorance is bliss and most people are just happy with whatever works. But (at least for me) once you see the difference between the shit AG6200 ones and the recommended color-accurate ones with less/no black crush, it'd be pretty hard to settle for the cheapo.

https://ultimatemister.com/product/mist ... ect-video/

Image

^ This site has super cool cables (like this one linked above, a SCART one & one with a DB9 connector meant for Commodore 1084/Philips CM8833/etc) intended for (15kHz) MiSTer direct video with the HDMI to VGA DAC built in. But they all use the AG6200, so it's a bummer if you're aware of the faults.

https://drive.google.com/file/d/15bpuRK ... 6mnbq/view
https://drive.google.com/file/d/1QSfjCy ... WII-W/view

^ Here's two comparison shots between an AG6200 DAC & the HDFury 3. Massive difference! There's plenty of other comparison photos on there, as well as in-depth analysis showing how close each DAC's output compares to reference-level RGB (see page 4)

I don't think I really suggest going to the lengths of spending $100+ on a HDFury 3 (I really lucked out and found one NIB for $40), it *does* look great in those comparison shots - but according to test results in the comparison spreadsheet, those IcyBox ones should be a real solid choice. Not 100% sure, but I also heard there is little to no remaining new old stock HDFury 3s on the HDFury site. They definitely aren't producing new ones and probably haven't for a long time. I also have the high-rated Vention (the one with the bonus HDMI passthrough), they used to be abundant on AliExpress but seem to have gone AWOL. I'm gonna go peek around now and see if those specific Ventions are back in stock on AliEx. I'll come back and post a link if I find some, but I wouldn't hold my breath. Again, those IcyBox units & other high rated units are gonna yield great results, hardly justifying spending WAY more on a HDFury 3 just for (potentially) a little better color accuracy.

Putting color accuracy aside: if there's people out there looking for HDMI to VGA DACs that can output higher bandwidth signals (there's a decent amount of chipsets that can do 250MHz or higher, some that even do 300+) for PC CRTs, that's a wholeeeee other can of worms. If you're going to be looking down THAT avenue, DisplayPort to VGAs are gonna be your best bet. No idea if there's any madmen out there who have tested any DP to VGAs for color accuracy... probably not. From all I can gather, those people are really just looking to drive the highest resolutions/scan frequencies they can possibly get. You can learn more about those from skimming around this thread, some people have also shared results of high bandwidth HDMI to VGAs in the thread - https://hardforum.com/threads/24-widesc ... nts.952788
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Re: HDMI to VGA Converter Black Crush Solution

Post by orange808 »

Guspaz wrote: Thu Nov 23, 2023 11:19 pm Here's a relatively recent example: https://jarrods.tech/laptop-latency-com ... s-optimus/

Keeping in mind that muxless Optimus (nVidia's marketing name for what is now a standard Windows feature but wasn't always) is the same thing as we're talking about here. In their case, they're getting 3ms of latency at 165Hz, which is half a frame at that refresh rate.

This is also a recent example and also testing at 165 Hz getting the same results, though using different tools: https://techteamgb.co.uk/2023/07/03/nvi ... explained/
That latency is quite reasonable. Thanks for the links.

I assume the "half a frame" time quote was a specific reference to 165Hz?

If not, I can't think of any reason why a slower frame rate would affect the time it takes to transfer information after a full frame is ready (and that "base" display latency time would change with the frame rate). Seems more likely to me that testing at 165Hz was chosen to push Optimus to the limit during testing. I'd expect to see about the same overall time penalty for using the feature at all frame rates. Wouldn't everyone expect to see a few milliseconds of additional latency at any frame rate--added to the other latency? (Instead of a flat half a frame?)
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Re: HDMI to VGA Converter Black Crush Solution

Post by Guspaz »

It could be, if you go back far enough to the early days of Optimus, you can find quotes like "According to Nvidia's engineers, the copying creates a latency of 0.2 of a frames."

0.2 frames at 60 Hz is 3.3ms, which is pretty close to what we're seeing with the modern screens at 165Hz, but by then it's half the frame.

I can also find reports from Oculus that latency impact can be different depending on the circumstances. Things like the dGPU rendering in a colour format not supported by the iGPU can force a slow conversion and put Windows into some sort of slow mode that adds multiple frames of latency, for example.
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