More confusion on house curves and target levels... - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 15 Old 08-06-08, 09:23 AM Thread Starter
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More confusion on house curves and target levels...

Hi guys,

The more I learn about REW and sub calibration in general the more easily I confuse myself (and that already easy enough!). I started thinking about my application of a room curve (7.8dB between 32Hz and 80Hz, in my case), and how I may be completely misunderstanding several things.
First, by application of a house curve am I not effectively cheating myself of headroom? In other words, the REW target curve is raised by 7.8dB at 20Hz (in my case), so wouldn’t that mean that a 20Hz signal would have its headroom decreased by the same amount? I’m assuming that measurement of the calibration pink noise is a measurement of the highest SPL in the 40-80Hz range.

Second, I originally defined my BFD filters by taking a raw response, manually adjusting the target level to a best fit, and played around with the filters on REW until I got a more-or-less flat response (relative to the house curve). My understanding is that any headroom lost by doing this would be regained when I calibrated the LFE trim from the AVR. I’m assuming, of course, that the AVR’s trim output is the final authority, and that a flat response (higher AVR trim?) and one with a house curve applied (lower AVR trim?) would even out (roughly).

Third, when REW empirically determines the target level, does a house curve have any effect?

Please, have no mercy in poking holes in my (incredibly faulty) understanding!

Peace... Vader

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post #2 of 15 Old 08-06-08, 12:42 PM
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Re: More confusion on house curves and target levels...

Great questions; I look forward to hearing responses from the gurus.
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post #3 of 15 Old 08-06-08, 01:10 PM
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Re: More confusion on house curves and target levels...

Quote:
First, by application of a house curve am I not effectively cheating myself of headroom?
Depends. If you simply added gain in the BFD filters to boost the signal over the business area of the house curve, then headroom is lost in the BFD.
If you added cut in the non-business area of the house curve then you haven't lost any headroom in the BFD, but if you subsequently raised the gain of the sub amp to compensate, then you've effectively lost the headroom again.

Quote:
calibrated the LFE trim from the AVR
The trim in the AVR is set before any filters are added to the BFD, and then it's never touched after that. The method of setting the input level of the BFD is covered in the BFD Guide.

Quote:
Third, when REW empirically determines the target level, does a house curve have any effect?
Yeah, if it modifies the bass management curve it will change where the automatic routine places the target level, but I would use the manual method to determine the optimum setting.

brucek
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post #4 of 15 Old 08-06-08, 01:43 PM Thread Starter
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Re: More confusion on house curves and target levels...

Thanks, Bruce. Looks like I have a little project this weekend... I think I have it correct, but I wanna go through with your clarification in mind and make sure.

One last question. Am I understanding that even if I manually move the target level up 8 dB in order to get a better fit, and apply filters based on that, and then subsequently reduce the sub gain by 8dB when calibrating to reference, effectively I have not lost or gained any headroom?

Peace... Vader

"Ya see, we plan ahead. That way we don't do anything right now. Earl explained it to me." - Valentine McKee

One sub to rumble them all. One sub to shake them. One sub to humble them all. And in the darkness break them....
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post #5 of 15 Old 08-06-08, 02:12 PM
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Re: More confusion on house curves and target levels...

Quote:
effectively I have not lost or gained any headroom?
No, it doesn't work that way. If you lose headroom along a path because of one device, there's no getting it back.

You have to first consider the BFD and ensure you're not adding gain to the point where it limits your voltage swing. Optimally, you'd like to feed it a maximum voltage when you're playing the receiver at its maximum you might ever use it.

So, if you monitored the input level of the BFD (hold down the IN/OUT button until it flashes) and played some bass heavy DVD at its loudest you'd ever use, have the sub trim adjusted to just see RED in the VU meter.

So normally, you won't see the RED LED in the VU, but if you are listening at loud levels some day and you have a bass heavy movie playing you may see the RED flicker. Of course, when the BFD is receiving this maximum voltage level, even a single filter of +1 dB (at that frequency that causes the flicker) will put the BFD into overflow. Avoid gain filters - they reduce headroom in the BFD......

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post #6 of 15 Old 08-06-08, 02:23 PM Thread Starter
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Re: More confusion on house curves and target levels...

ahhhhh now I understand (I think...). That is how I originally set my BFD input (all filters are negative), but I was not sure about the headroom stuff. I'm gonna check it this weekend, just to be sure. Thanx, Bruce!

Peace... Vader

"Ya see, we plan ahead. That way we don't do anything right now. Earl explained it to me." - Valentine McKee

One sub to rumble them all. One sub to shake them. One sub to humble them all. And in the darkness break them....
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post #7 of 15 Old 08-06-08, 04:37 PM
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Re: More confusion on house curves and target levels...

Quote:
Vader wrote: View Post

... I originally set my BFD input (all filters are negative), ...
But this doesn't mean that you're a negative person, Right???
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post #8 of 15 Old 08-06-08, 04:41 PM Thread Starter
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Re: More confusion on house curves and target levels...

Quote:
salvasol wrote: View Post
But this doesn't mean that you're a negative person, Right???
que rim tap....

Peace... Vader

"Ya see, we plan ahead. That way we don't do anything right now. Earl explained it to me." - Valentine McKee

One sub to rumble them all. One sub to shake them. One sub to humble them all. And in the darkness break them....
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post #9 of 15 Old 08-06-08, 04:49 PM
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Re: More confusion on house curves and target levels...

...

Quote:
Vader wrote: View Post
que rim tap....
... Is this good or bad???
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post #10 of 15 Old 08-06-08, 04:52 PM Thread Starter
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Re: More confusion on house curves and target levels...

Quote:
salvasol wrote: View Post
...



... Is this good or bad???
Good (I think).

Peace... Vader

"Ya see, we plan ahead. That way we don't do anything right now. Earl explained it to me." - Valentine McKee

One sub to rumble them all. One sub to shake them. One sub to humble them all. And in the darkness break them....
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