[Wayne A. Pflughaupt]

That’s the problem with setting the BFD’s input levels to maximum: It leave no headroom for boosting filters, if they are needed, or unexpectedly challenging program material – as you have seen.

The "set the levels as high as possible” recommendation dates back to the days when 12, 16 and 18-bit AD/DA converters were the norm in professional-grade digital processors - i.e., before the proliferation of 24-bit converters. Even the manual for my Yamaha digital parametric, an older model with 20-bit converters, recommends setting the input level as high as possible. But I’ve spent the last few days poring over the manuals of many digital pro-audio equalizers from Ashly, BSS, Klark Teknik, Rane, Sabine, Presonus, Alesis, Behringer, etc. – i.e., from cheap to ultra-expensive. All have 24-bit or better processing, and I have yet to find a manufacturer that recommends maxing out input levels as we typically do with the BFD.

Indeed, they hardly make any statement about input levels at all, as one would expect if it was as big a deal as we've been led believe. One manual that does mention signal levels, the Rane DEQ 60 1/3-octave EQ, recommends setting the gain level at ~10 dB below max. (Good advice for live sound applications; in our less demanding home environment we could probably go with ~5-6 dB [after applying filters, of course].) The BFD manual, another rarity that mentions input levels (some other Behringer EQ manuals are also silent on the subject), only mentions keeping levels out of the red. It does not state that levels are supposed to be pushed “as close to clipping as possible” in order to maximize performance.

Older 16- and 18-bit processors had a relatively high noise floor, which is why they needed their input levels set as high as possible. But what many people apparently don’t get is that higher bit rates have increased dynamic range downward, enabling an ultra-quiet noise floor and better resolution at low signal levels. Digital processors with 24-bit or better converters function identical to analog gear for all intent and purposes, which is why level setting has become a non-issue.

For instance, a 24-bit converter has a theoretical S/N ratio of ~140 dB. Of course, the BFD’s rather inferior converters can only manage about 95, but that still means an extremely low signal, say 50 dB, is 45 dB above the noise floor!

So – back off the input signal, or change the range setting, to get yourself some more headroom. Contrary to what you may have heard, the BFD’s noise floor is static. It’s not going to increase or decrease with varying signal levels. Anyone with the means to connect the BFD to their main speakers can verify this.

BTW none of filters I'm using add anything. All are used to subtract level from their specified bands.

Remember that cut-only filtering will lower the meter’s level with the EQ engaged. So when you see the meter hit the top, or close to it, that will mean your input levels are already clipping.

Regards,
Wayne