input lag used to drive me crazy 'till i found this app
http://cpsc.ucalgary.ca/~cheguo/File...tLagTestor.zip
it allows you to get an accurate reading of just how much input lag you're experiencing from any given input in milliseconds
if you're testing out your ps2-usb adapters, you might want to use joy2key or something
using this, i've found that my dilong ps2 to usb adapter adds very little lag whatsoever, neither does my usb refresh rate or lcd monitor
no matter whether i'm using a crt or lcd, a wired or wirelss keyboard, a usb joypad or ps2-usb adapter, i always get around 16.5ms of input lag
when i test this on my other two computers, i get between .5-3ms input lag
i've finally detemined that the extra 15ms or so is due to the nvidia drivers
i'm using an nvidia 9800gt, and from what i've gathered by asking others to test their input lag and report their results, is that nvidia just add's an unavoidable 16ms of input lag when you use their vidoe cards/drivers
it's quite a shame really
radeon's seem to only have about 4ms input lag
now 16ms might not seem that much, but it makes all the difference in the world when it comes to beatmania and ddr games in pc
stepmania has the 'global offset' feature, which allows you to enter the value of -16.5ms into the config file, which makes it pretty much dead-on
unfortunately i haven't found any way to make input lag adjustments for any iidx games on pc so far.
please give the app a try, and post you input lag and video card settings, just so i might be able to confirm some theories.