I didn't know about this. Thank you! I have another interesting thing to read up on.Unseen wrote:AC signals don't just couple to other signals by induction, they can also couple by the mutual capacitance of the traces that are carrying them.
This is absolutely it. Just like you, I get no noise exactly in the middle during that DRAM refresh. The spinning pattern matches the general interference I see during the FF6 title screen as well.paulb_nl wrote:I think the artifacts you are getting is CPU activity noise. Its more easily seen with the OSSC 256x240 optimized mode. I have captured a video with reverse LPF set to max so the noise can be clearly seen: https://youtu.be/syOW-w1q5UASamIAm wrote: I also replaced my APU's regulator and have mostly eliminated the big vertical stripe. What I haven't eliminated is a minor amount of diagonal noise. Again, I'd suggest looking at the FF6 title screen instead of LttP, because with all of my modifications so far, I get a perfect LttP title screen yet a slightly fuzzy FF6 title screen. I also still get weird artifacts near the top of the screen when the main FF6 logo appears.
If you take a look at this video where they visualize the CPU instructions timing you can see the noise looks exactly like that. https://youtu.be/Q8ph2OVqZeM?t=8m18s
There is no noise at the DRAM refresh in the middle where the CPU is halted. Also what they call spinning where the CPU is waiting for something looks the same too with the diagonal lines. Once the game is waiting for controller input at the save file selection the diagonal bars go across the whole screen.
I just now compared my two APU-01 systems. One has R59 and the RF unit removed, a new 7805, and a bunch of extra decoupling capacitors on the power rail, while the other is completely unmodified. Without a doubt, the unmodified system shows significantly more noise than the modified system. The modified system has virtually no vertical stripe, while the unmodified system has a plainly visible stripe as well as noise occurring at a different frequency together with the basic noise I see on the modified system. I suspect that removing R59 and smoothing the power rail each accomplished something, but the noise I'm seeing on the modified system is probably this CPU activity and not anything from PPU2.
It would be nice to figure out how to get APU boards to the same video quality level as the earlier boards. Anybody and his grandma could see that an unmodified APU looks awful during certain screens. Exactly what can be done, however, will probably need to be investigated by someone with more tools and knowledge than I have.
Thanks for the links and info!