BFD Input Level?

[lovingdvd]

brucek wrote:

The -10dBV setting is the most sensitive position, requiring less signal from the receiver...

Thanks. So is there any effective difference in how efficient my AV receiver is and/or how the sub sounds or its noise level if I have higher output at the receiver and lower input (+4db) at the BFD, versus lower output at the receiver and higher sensitivity (-10dB) at the sub?

LFE trim means receiver subwoofer output level (or whatever your model calls it).

brucek

Thanks for clarifying. Just a heads up that on the Yamaha receivers (and likely others) there are two different level adjustments for the sub. There is the general sub output level which controls the output level for everything related to the sub (LFE + bass sent to the sub for all speakers marked Small), and then there is also a specific LFE trim that goes from -20dB to 0 dB, specifically for adjust LFE (.1) signals only. So it could be easy for someone new to BFD/REW to misunderstand what you mean when referring to this as LFE trim.

[PeteD]

lovingdvd wrote:

I was under the impression that using filters that add boost is not advised. This may actually not be the case in your situation but I just wanted to make sure you were aware of that.


Can you please describe what you mean by "noise floor" exactly? Do you mean what you hear out of the sub when there is sound (input) coming down the line (noise during silent scenes)? How can I check my noise floor?

Noise floor is a lack of high signal to noise ratio, characterized in my case by audible noise in the system when the sound track is silent.

As brucek always recommends, if you can optimize your systems using only cuts, then do it. However, in some cases, the in-room response may necessitate such large cuts that there is not enough signal left at the back end - output of the BFD - to match the mains when the BFD starts to clip its input. In this situation, some people have successfully used the +4 operating level to prevent BFD clipping. I was able to do this, but because I had to have my receiver output cranked up so high (again because of some large cuts) - the noise floor in my sub and mains was not acceptable.

Now brucek correctly recommends using all cuts (remember a boost to part of a cut does not really count as boost) to maximize signal to noise ratio and dynamic range. However, in some situations (mine) this sacrifices general noise for the whole system and my system sounds much better with some substantial boost filters and the corresponding much lower noise floor associated with operating the BFD at -10. My system (a quad IB coupled with a receiver (H/K) that has a more gentle sub crossover that results in increased higher frequency output) is certainly not typical and brucek's mantra about avoiding boost should work for the vast majority of people. However, I firmly believe that if you need to consider operating the BFD at +4, you need to evaluate the noise floor of the overall system and consider using some boost filters instead.

[goatfarm]

brucek wrote:

LFE trim means receiver subwoofer output level (or whatever your model calls it).

brucek

LFE trim, at least on my receiver, is NOT the same as subwoofer output level. Rather it is a ratio or relationship between the LFE channel and the other five channels in a 5.1 configuration. It starts at zero (perfect +10 dB relationship) and goes down from there. There is a completely different adjustment for subwoofer output that is not related to the LFE channel. But I may be wrong here since this is my first post on this forum

I'm Greg. I love Home Theater. Been at it for years. Got a BFD, a corner sub and two powered towers. Would love to discuss the many ways to configure this system (I think I've tried them all).

All the best.

[lovingdvd]

goatfarm wrote:

LFE trim, at least on my receiver, is NOT the same as subwoofer output level. Rather it is a ratio or relationship between the LFE channel and the other five channels in a 5.1 configuration. It starts at zero (perfect +10 dB relationship) and goes down from there. There is a completely different adjustment for subwoofer output that is not related to the LFE channel. But I may be wrong here since this is my first post on this forum

I'm Greg. I love Home Theater. Been at it for years. Got a BFD, a corner sub and two powered towers. Would love to discuss the many ways to configure this system (I think I've tried them all).

All the best.

Yes this is what I've posted here recently. This is critical people understand this. Using the LFE level from -20dB to 0 on the Yamaha is NOT the proper adjustment for what setting BFD input level is like, and will mess up you sound pretty good - unless I guess all your speakers are set to Large. Otherwise you should use the general sub woofer output for this.

[goatfarm]

I'm not even sure why receiver makers put an LFE level adjustment on their equipment since it just confuses people. As far as I can tell from all I've read it should always be left at zero anyway. That's what gives the proper balance between the LFE channel and the other 5/6/7. Even with all speakers set to large and no sub, adjusting it would definitely have an audible effect since the LFE channel would be rolled into them.

[brucek]

I'm not even sure why receiver makers put an LFE level adjustment on their equipment since it just confuses people.

Well exactly. The THX specification imposes restrictions on the LFE channel, setting its volume to +10dB compared to other channels and limiting its bandwidth. The fact that some receivers add an adjustment for this level seems unnecessary. My Bryston SP2 processor has a THX Ultra2 spec and has no such control. In fact, no processor I've ever owned has had this questionable feature. It appears to be a new affectation from manufacturers to attract button pushing.

I didn't mean to steer anyone astray with the LFE trim reference, I was of course referring to sub out level.

brucek