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LFE Question


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#1 of 14 OFFLINE   BraveHeart123

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Posted January 23 2013 - 09:52 PM

Can anyone list some movies that have strict compliance to movie recording levels especially the LFE part? Some movies, e.g. Taken-1 has exeggerated LFE and I don't think it conforms to the loudness standards. The gunshots, though, sound great but are unreal. One more thing.....0dBFS means 105dB SPL on the speakers, but what about the same for LFE, which is already 10dB hotter?? Going by the book, the processor should clip any signal that's greater than 105dB SPL. If so, how does clipping kick in??? I am asking this coz um using BFD to tame the sub response and I am not too sure how it handles LFE that is already 10dB (115dB) hot when mains are playing at peak reference level (105dB)? Does BFD adjust itself for the bass frequencies and let the signal go unclipped till 115dB SPL or (120dB SPL including the redirected summed up bass from all the channels)?? I hope I've clearly stated what I need to clarify. Any thoughts on this??

#2 of 14 OFFLINE   Robert_J

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Posted January 24 2013 - 02:53 AM

The gunshots, though, sound great but are unreal.

All movie gun shots are unreal. There's very little bass in a real shot. http://s3.photobucke...nt=100_2776.flv

Does BFD adjust itself for the bass frequencies and let the signal go unclipped till 115dB SPL or (120dB SPL including the redirected summed up bass from all the channels)??

Don't think of the BFD in terms of in-room SPL. The box has no idea how loud your room is. It just passes an electrical signal and adjusts it based on the filters you set. I wouldn't worry unless your BFD's level meter is getting into the yellow or red area. Mine barely moves past the first green bar.

#3 of 14 OFFLINE   Dave Upton

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Posted January 24 2013 - 04:22 AM

My answer is extremely unscientific as I don't have waterfall plots to back this up - but Battle: LA has some incredibly realistic bass that doesn't run too hot.


#4 of 14 OFFLINE   Robert_J

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Posted January 24 2013 - 04:52 AM

My answer is extremely unscientific as I don't have waterfall plots to back this up - but

Battle: LA has some incredibly realistic bass

that doesn't run too hot. 

The last time I was there during an alien invasion, I said to myself "This sounds just like a movie I watched." Seriously, that movie does have some realistic sounding M4 / ACR rifle sounds.

#5 of 14 OFFLINE   BraveHeart123

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Posted January 24 2013 - 09:09 AM

I wouldn't worry unless your BFD's level meter is getting into the yellow or red area. Mine barely moves past the first green bar.

Hi Robert, if you are getting only the first green bar lit on BFD then you are at -40dBFS (65dB SPL). I assume, then, u must be dialing your ep2500 way way way up to get upto 115dB on LFE when your mains are hitting the full scale reference peaks of 105dB. Can you pls tell as to where your subwoofer trim level is on the avr??

#6 of 14 OFFLINE   Robert_J

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Posted January 24 2013 - 10:10 AM

I haven't checked in years but I think the AVR is set at +3 and the EP-2500 is 2 detents from all the way up.

#7 of 14 OFFLINE   BraveHeart123

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Posted January 24 2013 - 05:00 PM

its odd coz mine is at -3 and FL and FR are at 00 on avr. I manage to hard-hit the clipping lights on BFD at reference volume on some movies e.g. first car explosion scene in Killer Elite. What are your mains (FR/FL) set at on the level trims?

#8 of 14 OFFLINE   Robert_J

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Posted January 25 2013 - 12:54 AM

I'll see if I can find some time to connect a monitor to the receiver and see my settings. I may have to go back and revisit Battle: LA and see if I can push the BFD into the warning area.

#9 of 14 OFFLINE   BraveHeart123

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Posted January 25 2013 - 01:44 AM

I just wana check the relative trim levels of mains wrt sub. Pls send this info whenever you can. thanx

#10 of 14 OFFLINE   BraveHeart123

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Posted January 25 2013 - 07:24 PM

My answer is extremely unscientific as I don't have waterfall plots to back this up - but Battle: LA has some incredibly realistic bass that doesn't run too hot. 

Just watched different scenes from Battle LA. You r right, it has some of the best and most realistic LFE mix in it. Um running dual stacked subs that dig only till 22hz. The business area in this movie is mostly below 30Hz and a lot many times i think it plummets way below 20Hz. I guess I'd have to fire up my iNuke 6000 dsp and add my third DIY sub that goes till 16Hz. One odd thing though.....The last scene when the alien ship lifts off the ground, there is a tremendous subsonic impact. But there is not even half the same when the last missile hits it and blows it up. I was expecting bigger and stronger shockwaves. I think that should have been the other way around. Overall one of the best and most realistic war LFEs mixed in any movie.

#11 of 14 OFFLINE   BraveHeart123

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Posted January 28 2013 - 04:09 PM

Can somebody answer as to how BFD handles LFE signal. 0dBFS is 105dB peak, but that is for the mains. How does BFD handle LFE signal that is 115dB when speakers are playing Peaks at 105dB? Going by the book, it should clip anything hotter than 105dB max. But actually it should not or it will nagate the whole purpose of seperate 10dB hotter LFE mix. Need clarification.

#12 of 14 OFFLINE   Dave Upton

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Posted January 29 2013 - 01:12 AM

Clipping has nothing to do with the digital level (dBFS) as far as the BDF is concerned. You're sending the BFD an analog signal which is essentially voltage and current. As long as the level meter on your BFD isn't stuck in the red all the time, you're in good shape.

Here's an excerpt from the BFD Guide referencing setting levels:






Quote:

SETTING THE INPUT LEVELS ON THE BFD


After powering on the unit you will need to set the input level. The BFD is more commonly used in recording studio's and concerts, etc. It was not really designed for use in home theater systems nor for equalizing home audio subwoofers. When setting up a studio or concert, the level is usually the same. Most concerts I've ever been to keep the volume level the same (very loud!) during the entire event... they set it and forget it. At home we vary our volume level because we have several different input sources and different listening levels at different times. Our sources (DVD Players, CD Players, Tuners, etc.) usually have fixed outputs and they are in the audio chain prior to the pre/pro or receiver. The BFD is in the chain after the pre/pro or receiver. Plus we are not setting this on auto pilot and letting it search out frequencies to destroy feedback as the name of the unit would imply. It can cut a feedback frequency by up to 48db. We are using it as a parametric equalizer to tame subwoofer frequency response peaks... we surely don't want to eliminate them completely. Thus, we have to set the input level on the BFD so that during our maximum listening volume, it doesn't clip.
On the top right front of the unit you will see the "IN/OUT" button. Press and hold this button for a moment until the button light blinks. You are now in the "BYPASS" mode with no filtering active. You can only monitor the setting of the input level in the "BYPASS" mode. The input level is monitored by the LED's in the far left section of the display window. If the unit is not in the "BYPASS" mode then the LED's will monitor the "output" level. We want to monitor the "input" level. Play a CD or DVD with some good deep bass (U-571 with the depth charge scenes is a good one to use if you have it). Play the source at the maximum level you would listen to it. You should notice the green LED's moving up and down. You may only see part of or all of the green LED's lit or you may see all of them lit up along with the yellow and the red LED at the top lit (they will vary with input). The red LED at the top is labeled "CLIP". Your goal is to see the yellow LED close to the top blink on loud bass sections of the music or movies. It is okay if the red LED blinks occasionally as well... as long as it's not constantly lit. Remember... there's a reason it's labeled "CLIP". To adjust how far up the LED's blink you will adjust your sub output level on your pre/pro or receiver's speaker level menu or sub level control. (Your volume control on your sub has nothing to do with the input level.) On one of my pre/pros I had my sub level set to zero initially. After I connected my BFD I raised the sub output level to +3. This allowed the yellow LED and occasionally the red LED to blink during the loudest scenes of movies. Remember, the input level of the BFD should be set in the "BYPASS" mode (the "IN/OUT" button will be blinking). Once you have set the output level on your pre/pro or receiver you can then adjust the output level (volume control) on your sub to equal your mains. I used the AVIA DVD to match the levels of my speakers. AVIA instructions are easy to follow and the DVD will give you a host of other tools to use for video and audio calibrations. There are other DVDs and CDs available for this... such as DVE (DIGITAL VIDEO ESSENTIALS). You will also need to repeat the reset of the sub vs. main levels once you later complete the filter setups. You may find that once you have smoothed out peaks that your sub level doesn't seem loud enough. I had to turn my sub volume up for my taste. Remember not to adjust the volume of your sub via your pre/pro or receiver after you have set the input level... use you sub volume or the volume on the amp connected to your sub, which should be inline after the BFD.
NOTE: Something that you should remember to do when you are setting up your BFD is add a foot to the value you enter for sub distance in your pre/pro or receiver set up. The 1 msec DSP processing delay in the BFD would account for approximately a foot in distance.





#13 of 14 OFFLINE   BraveHeart123

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Posted January 29 2013 - 05:22 PM

Clipping has nothing to do with the digital level (dBFS) as far as the BDF is concerned. You're sending the BFD an analog signal which is essentially voltage and current. As long as the level meter on your BFD isn't stuck in the red all the time, you're in good shape. 

I already went through this article a long time ago. Anyway, I didn't get it when you say clipping is nothing to do with digital level. What is the point of signal processing and reference listening then?? Some movies do kick the bass into red clipping zone on BFD at -10dBFS on master volume.

#14 of 14 OFFLINE   Robert_J

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Posted January 30 2013 - 01:27 AM

Some movies do kick the bass into red clipping zone on BFD at -10dBFS on master volume.

Sounds like you need an additional sub(s) so that you can have the volume you want without pushing the BFD into clipping.




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