does this mean that in order to center the image using ArcadeOSD I need to turn off EDID emulation first, make the edits, and turn it back on?
Also, if I "copy modeline to clipboard" using ArcadeOSD, where do I paste it? mame.ini?
EDID enabled means you can centre every mode bar the one in the EDID, which is 640x480@30i for the desktop. It won't hurt to turn it off and turn it on again, i guess. You can always use the 640x480@60i instead, if it doesn't give you problems.
You copy down the three values you need. Below is the arcade_15 range line, showing where the values go in the mame.ini file's crt_range0 line. These are the values for HFrontPorch, HSyncPulse, HBackPorch respectively, and you can find them in ArcadeOSD when editing. Your values will be different, remember.
crt_range0 15625-16200, 49.50-65.00,
2.000,
4.700,
8.000, 0.064, 0.192, 1.024, 0, 0, 192, 288, 448, 576
This sets your range line in mame.ini. The other option is to take those new horizontal timing values, edit monitor.ini and redo VMM to setup your modelines again with the new values. IF find the former works best for me. And for specific machines or games you create neogeo.ini or ffight.ini files in the mame/ini directory, if needed, with the range line adjusted.