# Level on bfd too low ?



## Guest (Nov 16, 2007)

Onkyo tx-sr805
bfd dsp1124p


When trying to get a good level into the bfd I need to raise the sub output on my receiver to about +7 to start getting into the yellow. This is while playing wotw chapter 5. This seems way high to me especially when I read about others having the oppsite problem- to much level. This is also with the volume on the reciever at -28. I am using the -10 setting on the bfd and it's in bypass mode. I have an unbalanced rca to 1/4" from reciever to bfd and an unbalanced 1/4" to rca from bfd to subs. Should I be concerned about this? Does the onkyo have a lower than normal output voltage?

Also, when taking the bfd out of the picture and just running the sub out of the reciever to the subs and running the audyssey set up it has the sub level at -15 which seems right. Am I missing somthing here?

Mike.


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## brucek (Apr 11, 2006)

> Should I be concerned about this? Does the onkyo have a lower than normal output voltage?


There is a fairly wide range of output levels on different receivers. Unfortunately there is no real standard that everyone abides by.

There's not much you can do other than install a line amp between the receiver and BFD, but then you'll also be amplifying any noise that's there, so it may offer poor results if you attempt this - hard to say.

I see no problem in increasing the receiver sub output trim level as high as is needed to get a decent level to the BFD.

brucek


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

mrsnapper said:


> When trying to get a good level into the bfd I need to raise the sub output on my receiver to about +7 to start getting into the yellow. This is while playing wotw chapter 5. This seems way high to me especially when I read about others having the oppsite problem- to much level.


Not sure I’m getting what the problem is. If you’re able to adjust your subwoofer output so that the BFD’s meter gets up into the yellow, that’s perfectly adequate.

Regards,
Wayne


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## RazorX (Nov 7, 2007)

I apologize if this has been answered before but why do you need to have the BFD meter hitting into the yellow? Mine never gets out of the green no matter what I'm playing. I have my sub level set to 0 on the receiver setup right now. I can certainly bump it up to get it into the yellow but I'm curious why this is required/recommended.

Thanks,


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## brucek (Apr 11, 2006)

The BFD is a digital device. You want to make use of as many bits in the ADC chain. This provides the best S/N ratio and resolution...

brucek


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## RazorX (Nov 7, 2007)

brucek said:


> The BFD is a digital device. You want to make use of as many bits in the ADC chain. This provides the best S/N ratio and resolution...
> 
> brucek


OK. So, it provides the best S/N ratio and resolution. That helps but I'm not sure I understand why that would be the case. Why does having a higher input level on the BFD provide a better S/N ration and resolution than having a lower input level? 

BTW, What is ADC chain? Analog --> Digital Conversion?

Thanks,


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## brucek (Apr 11, 2006)

> Why does having a higher input level on the BFD provide a better S/N ration and resolution than having a lower input level?


Consider that you have no control over the noise floor of a digital device and are able to feed it a maximum input signal that is defined by 16 bits. That's 65,536 voltage steps to define your signal. The math will offer a certain dynamic range (~98dB) and S/N ratio from this situation.

Now lower the maximum input signal that you feed this system, such that the maximum level is defined by only 8 bits. That's 256 voltage steps above the fixed noise floor to define your signal. That's a loss of resolution. The weakest, softest signal is now lost in the noise and so the ratio of your maximum signal compared to the noise is considerably worst. 



> What is ADC chain?


Yeah, it's the section that converts the analog signal to digital.

brucek


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## RazorX (Nov 7, 2007)

Thanks for the great explanation. Now I understand why it matters and will adjust the sub output level on my receiver so I'm getting into the yellow on the BFD.


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

brucek said:


> Consider that you have no control over the noise floor of a digital device and are able to feed it a maximum input signal that is defined by 16 bits. That's 65,536 voltage steps to define your signal. The math will offer a certain dynamic range (~98dB) and S/N ratio from this situation.


Huh? The BFD has 24-bit converters. Twenty-four-bit converters have over *250 times* more voltage steps than 16-bit - 16,777,216, or a potential dynamic range of 147 dB. IOW, the converters have at least 50 db of “slop factor” before poor input levels get lower (worse than) than 16 bit.



RazorX said:


> Thanks for the great explanation. Now I understand why it matters and will adjust the sub output level on my receiver so I'm getting into the yellow on the BFD.


My goof, I thought the BFD had two or three yellow bars, but I see it just has one, just 3 dB before clipping. 

Keep in mind that if you run the input too high, you have no headroom for unexpected signal demands (doesn’t seem to matter which “demanding” movie you use to set your levels, sooner or later Hollywood will come up with something even more demanding). Probably best not to set it higher than about the –10 dB indicator. 

Regards,
Wayne


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## spudbudy (Jan 18, 2007)

Hi everyone I too suffer from too low a signal input.If I take my avr settings to the max is this where I will do my calibrations from? the starting point or do I change this level after I have all of my filters in place? Justy trying to get a handle on this


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## brucek (Apr 11, 2006)

> do I change this level after I have all of my filters in place?


The level feeding the BFD and entering filters etc are different issues. Generally, you want to get as high a level to the BFD as possible. This setup of its level by adjusting the sub speaker trim of the receiver is done once after installing the BFD and left alone after that. Not much you can do if your receiver has a low output. I wouldn't worry about it too much. If the level was extremely low, you could consider a line amp to raise the voltage level, but then you may introduce noise if the quality of the line amp is poor.

brucek


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## Matteo (Jul 12, 2006)

Out of curiousity, how much would a good line amp be, one that wouldn't introduce any noise? Any suggestions of where to get one??


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## mojogoes (Feb 11, 2008)

A friend of mine has a couple of monster 140w x4 line amp which cost around £2000 each.......there German or Sweedish/Dutch or something


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