i had the same problem too, fixed it with stepmania's global gap...here's the info on how to fix it brother
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Now, just play the game like normal. Ta-da! However, there is one thing youll need to set the GlobalOffsetSeconds. The thing is, on most pads, the timing is just a little off somewhere between the converter and the pad it is not as exact as you need it to be. There is one simple way to set the GlobalOffsetSeconds.
First, start a song, and turn on auto sync. Itll be in the second page of options. Then, play the song *as exactly as you can*. You will want to play something way below your level, a light song that you can AAA or something. Then, take the value it tells you at the end (itll probably be negative something) and put that into your GlobalOffsetSeconds= value (youll find it in \data\stepmania.ini).
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i got that from another forum! my redoctane metal pad now works absolutly wonderful with stepmania!
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Song Completeness
SINGLE = 4.32 %