I would think the DX7 and DX8 would be similar. My 3GX is -30% , 33% and 45%. I think on the Freddy Can Fly video he said to start somewhere around 33%. Anyway, I guess I must be happy with the 45% because I haven't changed it.
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I would think that you'll know pretty quick if it's a little high because of the tail wag.