I've been told the Subsonic filter is NOT always accurate, with some parts on amps made in bulk somewhere in china trying to cut costs, they can turn out to be less accurate with a subsonic filter resulting in a 20% variance. I guess what im asking is besides looking at the Hz marking alongside the subsonic filter knob, how else can a person figure out what Hz the filter is really set up to. I don't want to set up my filter based on the knob markings thinking its filtering everything below 31 hz when it really is set up to filter below 28 hz. So is there another way to set up the subsonic filter without assuming the standard markings on the knob are accurate. Thx 4 reading