I’m busy with things today, but I have a few things I can say here right now. I’ll post more later.
I have two working CRTs right now: In my dorm room, a 13-inch 1989 RCA Colortrak Remote with only RF, and at my home about 1.5-2 hours away, a 36-inch 2000 Panasonic CT-36D30B with RF, three composite inputs, one S-Video, and one YPbPr Component, all 240p/480i. I have a Dazzle DVC100 video capture that I can easily take from place to place.
My consoles at my dorm are an NES (front-loader, about 5 degrees skew per palette row) and a model 1 Genesis with rainbow banding, whereas at home I have a PlayStation 1 SCPH-900something with TonyHax and a roughly 2008-09 Wii. All of them either are modded or have everdrives.
I also have a 20-inch 1995 Toshiba CE20D10 with RF and composite, but it’s so broken and shitty with worn-out capacitors that I’ve been too afraid to power it on for several months. I did peek through the vents and see a TA8867AN in it, and my emulation of it looks convincing to me. I’ll have to go off of my memory for this CRT.
I’ve heard that RCA ColorTrak TVs had Toshiba jungle chips, but this one’s color is not like the TA8867AN. I’ll have to look closer, but this 1989 one reminds me of Sony’s JP axis.
Neither of these pre-2000 CRTs seem to be clamping off bright red at all. These CRTs are able to get very bright too before topping out. It’s as if there are no universal “1.0” or “255” RGB values in analog TV, and the video signal’s standard black and white IRE levels are just there to keep you from having to write down different CRT settings for each broadcast channel and video game console. My 1995 CRT made bright red and blue bleed over to the right if they ever got too high for the CRT to handle, and I would turn down my contrast and saturation to fix that. As for the 1989 one, I have to turn up my contrast and saturation almost to their maximums to start seeing this bleed, but it’s 100% there. This is why I think we shouldn’t clamp bright values at all, but we should still pull negative numbers up to 0.
Yellow definitely does not become orange on my CRTs. The only place so far where I’ve seen yellow turn orange is in Sony’s US axis chips. (Edit: I forgot to mention, these demodulators need to have their hue rotation and saturation (tint and color) settings sync’ed up. I have some quick code to match to color bars, but it’s not exactly right because it’s not in a perceptually uniform space. The shader has a built in test pattern to sync it by eye. One more thing to say, I have started using white C without chromatic adaptation, and I like the result much better.)
Last time I looked, I thought my 2000 CRT had Rec. 709 color over composite. If not, then it at least had a much less intense color correction compared to these older CRTs. It did seem to have different color over RF compared to composite, but I don’t know how to describe it.
Dogway has been inactive for some time now. We might have to contact them on another site. Still, about the BT1886, they didn’t define what happens if a value goes over Lw (or did they? I’ll have to look again), so I am just using the standard BT1886 function against the user’s brightness and contrast settings, while just tolerating out-of-bounds results. Not ideal at all.
About composite signal artifacts
My 1989 CRT has no comb filter, only the typical frequency filtering setup, with similar rippling artifacts to what’s in patchy-ntsc, whereas my 2000 CRT has a (probably adaptive) comb filter. Patchy currently implements lowpass and bandpass filters. I want to look into the adaptive comb filter that’s in cgwg-famicom-geom and consider incorporating it into Patchy.
I looked at a schematic of the VA3 model 1 Genesis and saw the part where the composite signal is being filtered. The thing is, I don’t know how electricity works. What I can gather is this. The circuit is relatively simple to use fewer components, but it’s trying its best to do a notch filter on Y and a bandpass filter on C. The CXA1145’s data sheet asks for a delay line on Y, but that’s missing on the Model 1 VA3. The resulting signal has a rainbow artifact pattern, even on solid greys and solid colors, not just on dithered patterns, and the rainbow artifacts can be reduced if not totally removed by replacing capacitors. Do you have any thoughts on these screenshots?
Speaking of real hardware, the filters I have are simple FIRs that go equally to the left and right. They should have a smear to the right instead, like an IIR filter, to match hardware better.
I haven’t looked at an SNES schematic, nor do I have a real SNES, but judging by a couple YouTube videos of video captures, I believe the SNES has no filters on its composite. I did see in a video from RetroRGB that the 2-chip SNES has blurry RGB, so implemented a simple bilinear blur for that.
I can imagine many CRTs used inductors and capacitors for their filters. I might look up some schematics and see if there’s any info on this. One mystery remaining is the sharpness setting in the jungle chip, which seems to take an already-filtered luma signal (or even the Y component of YPbPr in my 2000 CRT) and somehow sharpen it to restore detail that had been blurred out.
I’ll look at your noise, but I’m not too sure about it. A lot of noise in RetroArch so far is just random numbers. I think noise normally follows sine wave patterns in RF. The part I don’t know is what exactly those sine waves are and what distribution they follow. Is the noise really only from outside interference, or is there also noise coming from inside the console itself? This is just what I’ve heard while browsing the web, but the NES’s RF signal is known to consistently have jailbars, to the point that many people at the time complained about the RF-only toploader model’s poor video quality, so much so that Nintendo started installing modchips for composite video, and even made some rare ones with composite already in the console.
