# BFD Level Input Setup



## Guest (Feb 7, 2008)

"On one of my pre/pros I had my sub level set to zero initially. After I connected my BFD I raised the sub output level to +3. This allowed the yellow LED and occasionally the red LED to blink during the loudest scenes of movies."

This was taken from the BFD setup guide. I understand the logic, but do not understand setting the SW to +3, because then you have less room to adjust your reciever bass if you want to... 

Why not just set the SW to 0 on the AVR, then sub vol to match your mains. Then you have teh full 10 adjustment to play with on your AVR...


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## Wayne A. Pflughaupt (Apr 13, 2006)

The information in the Guide on level setting is wrong. When the Guide was written it was commonly accepted in home audio circles that the BFD’s levels must be kept as high as possible. However, this information was floated by people with little practical knowledge of or experience with professional audio gear. The truth is, the keep-the-levels maxed out theory is outdated. It was standard protocol in the days of 12- and 16-bit processors, but it’s is no longer relevant with modern 24-bit digital processors, which have substantially greater dynamic range and lower noise floors. And indeed the BFD manual does not state that levels must be kept as high as possible, only that you should not drive it into clipping (the red light).

You’ll often hear with digital processors, even modern 24-bit fare, that anything lower than the maximum input level means that you’re not using all of the digital bits available. However, it’s generally accepted in the professional recording field that once you’re above 16 bits, optimizing signal levels is no longer an issue. This is because a 16-bit waveform, which has 65,536 amplitude or quantization “steps,” is considered the threshold of what is acceptable for hi-fi sound, because at that rate the human ear can no longer detect quantization errors at low levels. However, a 24-bit waveform has over *250 times* more amplitude “steps” - 16,777,216. It should be obvious that a 24-bit waveform, even with a fairly low signal level, will deliver dynamic range figures and low-signal quantization well in excess of 16-bit, which delivers a noise floor of ~96 dB. 

Others here have their own thoughts on this; maybe they’ll chime in. Mine is that as long as you have a reasonably healthy signal on the BFD's meters you’re fine. If you want to go the maximum level route, top it out at the –10 dB mark. That leaves you some headroom, because they always seem to be coming out with something “bigger and badder” in the bass department.

Regards,
Wayne


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## brucek (Apr 11, 2006)

> do not understand setting the SW to +3, because then you have less room to adjust your reciever bass if you want to...


The adjustment is there to use for this exact situation. Once it's set for your equipment, you'll not likely need too much further trim.



> Why not just set the SW to 0 on the AVR, then sub vol to match your mains.


Because you'll not be taking advantage of as many bits as possible in the BFD. 

As you decrease the input signal, the noise will rise exponentially. Once the LSB and other low order bits are gone as a result of the low input voltage the A/D is no longer a 24 bit device, but a lower bit device, producing higher noise figures. Digital electronics may have gotten better, but the math has not changed....

brucek


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