[Wayne A. Pflughaupt]

Hmm... Well, you’d want a low shelving filter – but I guess you already figured that out. Don’t know exactly how the DSP 30 works, but I did see in the specs that the shelving appears to be pretty flexible, with adjustable Q. I’m not really sure how Q functions with a shelving filter, but I’m guessing it affects how broad or steep the action is. You’ll have to experiment with that – REW can easily give you a visual of what’s happening.

As far as actual adjustment, you’d first determine the slope you want using the 100 Hz – 30 Hz sinewave test I described (or whatever upper and lower frequency markers you decide to use). Ultimately that’s what you’re shooting for, 30 Hz at 0 dB, 100 Hz at –6 or –8 dB, or whatever your target is.

Hopefully the turnover frequency is adjustable – otherwise the filter will be of no use. Set the turnover frequency down low, say 25 Hz, possibly lower. This is because typically response will actually “hinge” at a higher frequency than the setting once you cut the filter. At least, that’s the way it usually is with analog filters. Digital filters – haven’t used one, you’ll just have to see. I have a feeling the Q setting may also affect how quick response changes at the turnover frequency – again, use REW to see.

So basically, cut the filter for the amount you want 100 Hz to be attenuated, then play with the turnover frequency and Q settings until response starts hinging downward at 30 Hz or so.

That’s about the best I can tell you – hope it helps.

Regards,
Wayne