Reply To: Pre ADC Gain Controls

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#21042
yoshiyukiblade
Participant

This is definitely a nice option to include in the firmware. I don’t have a 1CHIP SNES to test it on, but I did mess around with it a bit on my older model SNES. My unit seems to output a weak signal. Working backwards from the equation in James-F’s post, it would have to be under 0.65 V for the peak input. Pushing the coarse gain to 1.4 appeared to be fine, but 1.5 showed signs of clipping, even if it should theoretically be OK (less than 1.0 after multiplication). A pure white screen isn’t at 255 at the output either. I’m not sure why that is, but I’ve been basing the output values off of lossless RGB recordings made in OBS, so anything along that video chain may affect the final output.

Interestingly, I found no immediately-visible differences between high coarse/low fine gain vs low coarse/high fine gain. I tested coarse gains at 0.8 and 1.4, saving each setting to their own profiles and switching between them; they looked pretty much the same to me. I was assuming that pushing analog gain close to 1.0 would be most optimal, similar to “exposing to the right” (ETTR) in digital photography, but it doesn’t make much of a difference in the end.

On a side note, the output video on the test firmware was odd. The best way I can describe it is that it was outputting 4:2:2 or something. Optim. mode colors were not clean, but the resolution was fine, judging from the black-and-white checkerboard pattern in the 240p test suite. I could kind of salvage the video output by sampling at 682 and setting the active area to 512, but it’s not as good as it should be.

That’s all for now. Thanks paulb_nl for providing us with a test build!