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Discussion Starter #1
I have an Onkyo 886 and I'm using a DSP1100 w/the RCA output to drive a HSU VTF1. I'm also using the XLR output from the 886 through a DSP1124. the XLR output goes to an EP4000.

I know I could feed both RCA and XLR through just the DSP1124 - but for now I'd prefer to separate it.

However, what I've noticed is that even with both on pass-through mode (showing the signal level on the BFDs) the DSP1124 that's being driven by the XLR output of the receiver will show clipping periodically while the DSP1100 thats driven by RCA does not. The level on the 1100 is very high, however.

I know that Pro-audio XLR outputs have a higher line level than consumer-audio RCA gear -- however based on my experience, the 886 XLR output is higher than consumer line level -- but not as high as Pro-audio voltages.

What impact would changing the input level selector on the 1124 to the +4dDBu setting?

Thanks in advance!
 

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What impact would changing the input level selector on the 1124 to the +4dDBu setting?
Switching to +4 will raise the BFD’s noise floor considerably, but fortunately that isn’t a concern with subwoofers.

To gain a better understanding, the-10 dBV and +4 dBU operating ranges the BFD has can be thought of as an internal gain structure. Since there is a 20+ dB difference between pro and consumer nominal signal levels, one gain structure cannot be optimized for both ranges. In other words it’s impossible for a processor to deliver, at the same time, the best headroom and the lowest noise floor from a single internal gain structure. The higher-level (professional) +4 dBu range will have the best headroom, while the lower (consumer) -10 dBV range delivers the quietest noise floor.

(As a side note, the range settings on a SPL meter operate the same way, providing a balance between the mic pre amp’s noise level and the expected volume of the signal being measured.)

Gain switching on pro devices isn’t as common as it once was, as electronics technology has improved noise floors to the point that pro manufacturers can largely stick with the +4 dBu gain structure. These days you’ll only find +4 dBu / -10 dBV switches on the BFD and similar low end pieces.

Regards,
Wayne
 

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Discussion Starter #3
Thanks for your comments!

Since the XLR 886 output then is a touch higher than the consumer RCA output.......... Do you think that maybe it would make more sense to leave as is - and periodically clip a little bit w/the BFD........ Or maybe get a converter to boost the XLR output a little bit to be true +4 dBu level?

Which would be nosier? The BFD with a +4 dBu setting as is - or using a level matcher to amplify up to the +4 dBu setting?

I guess I've always been fuzzy when it comes to noise floors - and what is a bigger factor in noise - the amplifier or a device that has a wide range of input voltages. I assume the noise floor grows - because with +4 you just increased the range of voltages that it can accept - but won't really see from a consumer audio device.

This just occurred to me - and maybe it's most practical.... The LFE output on the 886 is currently set to -2 db. I actually had it set quite a bit lower because the HSU-VTF1 has such a high gain --- and then had to raise it because the EP4000 was much less sensitive (probably expecting a real +4dBu).

Would lowering the preamp LFE output a few more db - and running the amps a little hotter make most sense?

That should theoretically keep the noise floor as is with the BFD and give a little more headroom.. right?

Sorry for the rambling!!
 

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I guess I've always been fuzzy when it comes to noise floors - and what is a bigger factor in noise - the amplifier or a device that has a wide range of input voltages.
Every piece in the signal chain is important to the system noise floor. The system can only be as quiet as the noisiest component.

Since you have separates it’s easy for you to get a grasp on the subject. Just try inserting the BFD across your main speakers and switch between the two gain stages, with the pre-amp’s volume up at your normal setting with no signal present (i.e., switch to an unused input). You’ll probably find that even in its -10 dBV setting, the BFD will add noise. Switch to +4 and it goes through the roof.


Would lowering the preamp LFE output a few more db - and running the amps a little hotter make most sense?

That should theoretically keep the noise floor as is with the BFD and give a little more headroom.. right?
I intended to mention adjusting the preamp/amp levels, but it slipped my mind while composing the post. That will get the BFD out of clipping. However, the BFD’s background noise levels are fully independent of the signal level it receives - that's why a signal boosting device won't make a difference. Fortunately, poor noise floors aren’t audible with subwoofers, as long as they don’t involve hum artifacts.

Regards,
Wayne
 

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Discussion Starter #6
I ended up having to change the level setting on the BFD1124 via XLR.

I set the LFE output back to -5, and it made almost no difference on the level - and I didn't want to keep setting it back since it would also set the RCA output lower.

After changing the level, the BFD is much happier. It still seems to get high on the meter - but just doesn't clip anymore.

Which is good.. because some noises I heard before were indeed audible clipping!
 
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