Atari 800XL Input lag: hardware via s-video LCD vs Altirra emulation

[donjn]

I recently purchased an Atari 800XL with an s-video mod and an UnoCart to go with it.

 

I also recently stumbled upon this beauty below. A Magnavox, 15" 4:3 ratio TV (it actually has HDMI too which is rare for 4:3 ratio TVs).

 

I am worried as bit about the lag which I am very sensitive to. The easiest game to test lag for me is firing up H.E.R.O . and moving back and forth rapidly. Altirra emulation n Windows 10 on my gaming machine is quite good and lag is almost not noticeable.

 

So my question is this, which would have worse lag:

 

1. Atari 800XL emulation on the Altirra on Windows 10 on a very fast computer.

2. Real Atari 800XL hardware hooked up via s-video to this tv/monitor?

 

Here is the Magnavox tv:

 

 

 

[phaeron]

I don't have precise measurements but unless your TV has a heavy amount of postprocessing delay the 800XL will most likely win. There are just too many delays inherent in the computer's input->OS->program->OS->output paths. Just generating whole frames and resampling from the Atari's actual speed to the display's refresh rate incurs ~1.5 frames of delay, while the Atari is scanning out its display with zero delay. You can probably get the difference lower if you use a video card and display combo that supports adaptive refresh rate. Pairing the 800XL with a CRT would probably beat both, however.

[suspicious_milk]

Emulation for modern displays; whatever, you're emulating anyway.

 

Real Atari's for CRT's.

 

The input lag with a real Atari on an LCD/LED Display is horrid.

 

You can't beat 0ms response. You just can't.

[+slx]

 

Real Atari's for CRT's.

 

The input lag with a real Atari on an LCD/LED Display is horrid.

 

You can't beat 0ms response. You just can't.

If they werent so bulky. Even with CRTs available for next to nothing these days theyre just too large to stock up...

[Rybags]

It can vary depending on the TV.

 

Using HDMI input there's likely not much lag, maybe a frame at most, so 1/60th for NTSC.

Using S-Video chances are it's doing frame blending so probably 2 frames worth of lag or maybe even worse.

 

You'd probably find it hard to notice less than 3 frames worth of lag but every chance that you might be experiencing worse.

 

To determine how much lag you have you'd want a program that immediately flashes the screen while starting a loud sound, preferably have the sound commence at the start of Atari's vertical blank interval which is in fact a little time befor the actual vertical blank - pipe the audio directly from the Atari to some external speakers so you can guarantee that there's no lag occurring there. Then use a camera at preferably 60 fps capture to record what goes on. Then load the video into a suitable editing program and work out the delay from the start of the sound until the colour changes.

[donjn]

Or should I just run my Atari 800XL via composite to this?

 

[256 colors]

I don't ever recall having lag problems on a hdmi tv/monitor using Altirra

Real Atari hardware on a analog crt tv/monitor/pvm/bvm little or no problems

Real Atari hardware on a on a modern hdmi it's not going to be the same from analog output into digital input

Edited March 27, 2019 by 256 colors

[Daedalus2097]

While HDMI itself won't introduce much lag, quite often the image processing carried out by the TV does, and that can be applied to any input - analogue or digital. Things like dynamic contrast ratio (ugh) and similar effects need to analyse an entire frame, then adjust the TV accordingly before actually displaying the frame.

 

Check if the TV has a "gaming" mode in amongst the colour and contrast settings - many do, and it removes steps from the processing, resulting in certain features being disabled but reducing the lag to the lowest possible using that display.

[donjn]

While HDMI itself won't introduce much lag, quite often the image processing carried out by the TV does, and that can be applied to any input - analogue or digital. Things like dynamic contrast ratio (ugh) and similar effects need to analyse an entire frame, then adjust the TV accordingly before actually displaying the frame.

 

Check if the TV has a "gaming" mode in amongst the colour and contrast settings - many do, and it removes steps from the processing, resulting in certain features being disabled but reducing the lag to the lowest possible using that display.

This small LCD TV has very few post processing options. Just things like sharpness, noise reduction and dynamic contrast. I assume set all of these to zero or off?

[Daedalus2097]

Hmmmm, I would try setting them all to 0 anyway, but it might not make any difference if the processing stage is permanently enabled and so keeps the lag. That's a shame.

[suspicious_milk]

It can vary depending on the TV.

 

Using HDMI input there's likely not much lag, maybe a frame at most, so 1/60th for NTSC.

Using S-Video chances are it's doing frame blending so probably 2 frames worth of lag or maybe even worse.

 

You'd probably find it hard to notice less than 3 frames worth of lag but every chance that you might be experiencing worse.

 

To determine how much lag you have you'd want a program that immediately flashes the screen while starting a loud sound, preferably have the sound commence at the start of Atari's vertical blank interval which is in fact a little time befor the actual vertical blank - pipe the audio directly from the Atari to some external speakers so you can guarantee that there's no lag occurring there. Then use a camera at preferably 60 fps capture to record what goes on. Then load the video into a suitable editing program and work out the delay from the start of the sound until the colour changes.

 

That all sounds pretty complicated. I just see how many levels of Defender I can beat. Easily blow past level 30 on a CRT and struggle for 20+ on any modern display. :-)

[donjn]

Another thing to add, my NES Classic as pictured runs with almost no lag at all. And I was able to mod my NES Classic and play SNES and Genesis games through Retoarch (an emulator) with no lag either.

 

So if SNES games run great through NES Classic using an emulator, wouldn't a direct Atari 800XL straight into s-video have minimal lag as well? Or does the fact that NES Classic uses HDMI make a big difference?

 

I guess I will know in a couple days.

[+Nezgar]

Even 1 just frame lag on 60Hz NTSC is 16+ms added lag (1000/60) and 20ms on 50Hz PAL. I suspect this is the absolute minimum for any modern LCD/digital display decoding an analog source, as it will only process the data for display AFTER it's received a complete frame...

 

Also highly likely that it will delay for at least 2 frames, as normal broadcast 480i needs two 'fields' to complete a 'frame' so some TV's are highly likely introduce more delay... then 3D comb filtering needs at least 1 more complete frame to compare to the previous and process that... etc..