# Difference between +4db vs -10db input level



## lovingdvd

I've read in the setup guide that it is highly recommended to use the -10dB (home) input level on the BFD instead of the +4 dB setting (studio).

When I first set up REW/BFD months ago I accidentally had the switch in the +4 dB setting and didn't realize it until well after I was done calibrating the filters and getting everything set up just perfectly. Not wanting to mess with an otherwise perfect setup I just left it that way.

Fast forward several months to the present and I now have a new receiver and therefore went through the complete REW/BFD setup again from scratch. This time I did so at the -10 dB setting since I knew it was recommended.

However I am trying to understand exactly just what difference the +4db versus -10db setting actually makes. For instance when I look at the lights on the BFD showing the input level, they do not seem to change at all based on the +4 vs -10 setting. So when I play a loud passage with deep LFE bass say it flashes orange at loudest part with +4db. When run with -10db it gives the same exact reading with the lights.

So what difference is this setting actually making? It does not appear to affect the input or output of the sub, but I'm sure there is a notable difference here somewhere - just trying to understand what that difference is.

On a related note my bass does not have as much 'thump' with music as it did with my last configuration despite having about the same response curve and house curve post calibration. Is it possible this setting is playing a part in that? 

Thanks!!


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## bobgpsr

Normal home usage receivers (AVRs) use the nominal line output level convention of -10 dBV so IMO best to use that into the BFD. Less chance of having your receiver output clip. The BFD should output a nominal +4 dBu pro level to a downstream amplifier.


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## lovingdvd

OK, I think I see now. This is dbV, not db? Not that I know what dbV is necessarily  but then this is not a measure of the actual loudness like db would be?


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## brucek

> This is dbV, not db? Not that I know what dbV is necessarily but then this is not a measure of the actual loudness like db would be?


The two operating level switch settings are -10dBV and +4dBu.

The 0dBV reference level is 1 volt and the 0dBu reference level is 0.775 volts.

The switch doesn't change the level or affect the signal that it passes in any way through the unit. It simply changes the operating level.

Send a continuous peak signal sine wave from REW into the BFD with the switch set at -10dBV and then switch to +4dBu. You will see the LED indicator LED drop quite a bit....

brucek


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## thxgoon

I changed mine the other day after seeing red clip lights on the BFD. It was my (wrong) assumption that this would attenuate the input level and require more gain from the amp to achieve the same volume and this is how the BFD gained headroom. WRONG!! I clipped my amp.

Running noise to the sub and switching back and forth between the settings there was no difference in output level. Apparently just the internal processing levels are different.


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## Wayne A. Pflughaupt

Yup – it’s internal. Some equalizers have a switch separately for the input and output, and those _will_ make an audible difference in level if you switch one but not the other.

Regards, 
Wayne


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