I don't understand the BFD clipping meter. Please help.

4229 Views 28 Replies 3 Participants Last post by thewire, Mar 2, 2009

thewire

Discussion Starter · Jan 21, 2009

I was watching Master and Commander at around +5 reference and it sounds great, but I notice that the BFD clip light comes on. I use the +4 setting on the back. I also notice that the right input meter begins to light up and clip as well when the left side (input I use) is clipped. Why does the right input meter light up? What exactly does this do to make the sound less good sounding? It does not clip my sub amps or bottom the subs. Thanks.

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thewire

Discussion Starter · #3 · Jan 21, 2009

brucek said:
Turn down the receivers sub out trim level.

The channels are completely independent. If you feed information to both channels they'll both respond.

It will add considerable distortion to the signal when it clips. Digital clipping is not elegant like analog clipping is. Reduce the input level to the BFD.

brucek

Would digital clipping send my subwoofers MA-500 mono amps into protection mode as it does when I send a high level to the MA-500's that power my mains instead? My amps can go into protection quickly with a compressed CD at a moderate level.

The BFD dynamic range is much less than my amps.. I think, probobly hence the 15dB headroom. The gain I have control over is the master volume or the output on the pre/pro. I can turn down the output from -4 to around -8 and apply a couple small filters and loose around 10Hz extention. Should I try that instead of the 25Hz for listening louder, or do you think I should listen at an overall lower volume level?

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thewire

Discussion Starter · #5 · Jan 21, 2009

Sorry I meant the FBQ which is what I have. I will show my options in a couple graphs here. I can't seem to get clipping on the FBQ with more than a -4 setting lower than at -2 on the master volume. You can change the thread tile if you like. Not sure I can do that.

If I simply lower the output I'm sure I could get some higher midbass but not sure it if it is worth the extention. I will show you what I mean in a couple graphs here soon. The output I measure in REW is -2dB lower than when I measure from the CD player (analog) source so it looks slightly lower. I have it calibrated on the pre/pro where -20dB FS Pink PN equals 85dB on my meter (master volume at -5 which I reffered to as reference) when checking the CD player, and making the response track the target. I have done a comparison between using a CD versus using a DVD with some pink noise at -1dB FS and they looked the same level.

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thewire

Discussion Starter · #6 · Jan 21, 2009

Here are some graphs to illustrate what I mean by using some smaller filters with a 35Hz target level instead of the 25Hz one.

The first one I use currently REW says there is 13.6 headroom. The second with no eq said 7.1 headroom, and the last one adding one of the mains had zero headroom. This maxs out at around 2Khz, which I have been able to remedy in the past by placing a blanket over the couch near the mic. The mic was aiming up wedged between two seats centered in my front row at ear level. I changed the target to track 82dB. To get a 75dB target in REW I must lower the master volume -10, but my input in the VU meter reads around -24 instead of -18 so I like using the volume I listen more commonly at. This is -4 on the sub output in the pre/pro, -5 for the master volume. No amp gain adjustments on the four MA-500's I use to power the 4 12" drivers which are placed each around 3' - 4' from each rooms corner. Two are on the stage and two are on Helmholtz Resonators in the back.

Any thoughts if I should lower the pre/pro master volume versus lowering the sub output? I really can't ever recall hearing any kind of digital clipping. Not sure about seeing the next side light up. Maybe I was tired.

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thewire

Discussion Starter · #7 · Jan 21, 2009

I forgot I lost the 35Hz area when I changed one of the subs phase in the back. The other would look like this but I think I had used a higher SPL level but lower target for this graph. I seem to feel more bass with the other graph after eq.

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thewire

Discussion Starter · #8 · Jan 22, 2009 (Edited)

Here is what I get if I move the subwoofers to the corners (on the floor front, platform back) and move all seats forward. This puts my seating locations back where they were. The sub measurement was taken before 2 Pillar Traps and 2 GIK 244's were adjusted. The center channel looked so-so in my measurement before I realized it was off center. There is better looking decay in the waterfall at this 90dB target in the back of the room than the 85 in the front. This would allow me to turn down the gain and still enjoy the subwoofers, but I would be moving to the back row to sit. I had to move my surrounds also. The full range measurement has 1/3 Ocatave smoothing. I didn't adjust anything yet except the speaker levels not counting the sub and the mains are not to the exact inch. The mic was aimed at 45 for the mains response. What do you think?

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thewire

Discussion Starter · #9 · Jan 22, 2009

There is one thing I forgot to mention also. Something strange happened while I was setting things up. After I took the XA2 off pause (just like when I saw the FBQ clipping madly), the center channel amp started going into protection no matter what level I set the master volume or level trim. I ended up turning off the player and turning it back on and then it quit going into protection mode.

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thewire

Discussion Starter · #12 · Feb 1, 2009

I was having lunch.

I should have followed up on this thread. After I have looked at the back of the FBQ the -10 setting was in fact engaged. The level does not sound that loud. I was only getting a 100dB peak in Jurrasic Park at the scene where the T-REX does it's big roar at the car after they climb over the cliff and the car falls. I will recheck what I am getting now. I have changed my subs locations, used much less eq, and the gain is at -6 instead of where it was before. I have been listening to -5dB reference (THX optimizer = 74dB -75dB) instead of louder.

The scene that caused the clipping on the meter was right after I took it off pause after the scene where they must cut the mast down. The scene was over and I only hear a very faint rumble from the next room as I was in the equipment closet. I did not hear any highs or midbass from the room during the clipping. I will give it another try today (not as loud a setting on the master volume) and see if getting the setting right helps. :hide: That's a good tip about the crosstalk. :T

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thewire

Discussion Starter · #14 · Feb 1, 2009

Must have been 90dB in Jurrasic Park I was thinking of. The 100dB must have been Master and Commander somewhere. I'm now getting 87dB for the same T-Rex roar at +5dB reference. While the T-Rex was walking I looked at the VU meter and there was one light lit up.

I will check Master and Commander...

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thewire

Discussion Starter · #15 · Feb 1, 2009

Andysu said:
Lunch okay I see, I see.

I know the moment in the film and yes I have Jurassic Park DVD JPII on THX dts laserdisc and JPIII on DVD all DVD are region 2.

I’m surprised you didn’t notice the clipping during the opening “down all hands down!”

Keep it at +4db this will prevent crosstalk and both LED indictors illuminating.

I’ll start up the SONY CRT loud up the film and run some tests at silly levels, don’t worry not a chance I’m going to bust anything in. You might want to consider DCX2496 it’s a lifesaver.

Yes actually I checked that part first and the lights did not clip. There is a moment while the cannons are all shooting and the guy in the red vest is waving his sword and the hole room feels like it's exploding.

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thewire

Discussion Starter · #17 · Feb 1, 2009

At reference level (master volume 0) I am getting 106dB uncorrected C-weighting slow, for "all hands down" and the FBQ is at the fourth LED but was staying mostly around the third.

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thewire

Discussion Starter · #18 · Feb 1, 2009

Andysu said:
Just as I suspected -10db is bad news. “Down all hands down!” will send it into clip and +4db at best is 12db at 0db on the Kenwood KRF-X9050D with LFE.1 at 0db.

So you probably didn’t notice it until about chapter 15. You don’t have the LCRS diverted to sub by any chance?

Right now I have each speaker crossed over in the XA2 DVD player except for the left and right at 80Hz and the internal crossover on my Outlaw 950 engaged also. The Outlaw diverts bass whether I flip the switch on or off. I was measuring my center and surrounds with the crossover on the Outlaw engaged the other day and it was not redirecting bass for the surrounds or the center. I'm still only experimenting with having that engaged. As it is, I had to put speakers in my center channel that were from one of my other mains I am not using because it would distort. I was noticing that the bass from center channel would reflect off the couch on eather side of me last I was trying without the crossover in the player on. I was told by Polk they matched close anyways. I have been focussing mostly on getting the center channel to sound better lateley. I am trying to listen for a problem, and it seems the dip in the center channel I measure is like my left and right speakers, except somewhat deeper. I can't explain why 100Hz -150Hz measures so high in it, but I suspect it is something to do with the drivers being mounted horizontal.

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thewire

Discussion Starter · #21 · Feb 1, 2009

When I measure each channel I turn off the amps that I am not measuring. The last time I measured with the output of REW directly into my pre/pro input and I measured with the center and subs, then the center without subs and I saw no difference. It was the same for the surrounds. I will check again since I have done this before and I did not see this happen. I noticed when I checked the output of my player with a CD using Pink PN noise I made using REW, that my center channel had lower output around the crossover. It may have been some fluke that I am not sure how I did, so I will recheck.

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thewire

Discussion Starter · #22 · Feb 1, 2009

I think I know what might have caused it. I was recently using my CD input for Stereo Bypass mode and since in this pre/pro you have to do some switching or other, it may have turned off the crossover for the other channels when I tried using the 6 channel bypass mode again. I'm pretty sure I had turned off everything and switched inputs. Maybe I need to go back and disable the 2 channel bypass for the stereo analog inputs, or if I don't need to now, I should have then.

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thewire

Discussion Starter · #24 · Feb 1, 2009 (Edited)

It looks like the crossover for the center and surrounds works again. When I had switched the polarity on my center when I was testing my center with the Pink PN from the player, I get a very large dip in the 138Hz area (aproximate), but the 100Hz - 150Hz area is lower like the left and right. This what levels look like in the pre/pro after using the optimizer. I turned off the crossover on my DVD player and without doing a recalibration checked to see what changes I got in SPL.

One of my subs may have, or may not have been off when I measuring just earlier. A pair of the bannana plugs woln't turn well on my one my subs amps so they are laying inside and can fall out if I'm not careful. I measured a 105dB peak at the begining of Master and Commander at reference level.. Maybe I should give War of the Worlds a spin again.

Still not sure what to do about this center channel. I could try using one of my other mains placed horizontal to see what difference that makes. It doesn't look good at all as it is. I'm tempted to not even use it. This is with the mic pointed up in the front row center. The left, right, center are about 6 feet away and this is 1/6 smoothing.

Blue = center

Red = left

Green = right

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thewire

Discussion Starter · #26 · Feb 1, 2009 (Edited)

Thanks Andysu. I have thought about one of these DCX2496 before and it keeps looking more and more like what I need. You can see on my graphs here my subs require a bit of tweeking after the crossover as the slope is not steep enough. When I equalize from a 80Hz crossover point and eq the 90Hz bump, it results in a flatter looking response for my left and right channels.

The center I checked out and it is in phase according to my volt meter. I went inside and removed some extra damping material I added in there some years ago, and the extra dip went away. I also noticed my new replacement tweeter was out-of-phase in comparrison to my other mains. It's no wonder I was having so many problems with it. Now this makes me wonder if the extra damping material I placed behind the lower drivers in my towers that had none are not having some kind of negative effect. I'm also not sure if increasing the volume in my subs by removing the displacement caused by the plate amps enclosures is not somehow increasing the output above the crossover area to high. When I measured near field I did not notice such a bump however so it could only be something to do with my room modes at 80Hz which I was aware of when designing the room. So I might be able to correct this with a custom roll-off instead of using the eq to do so. It makes it difficult to set levels when I need to add eq after my crossover, but if I do calibrations in REW with sweeps instead of using these Pink Noises to set levels I get it looking better.

I tried this time with the polarity on all my subs reversed and I also checked the center to see that it was in-phase with the voltmeter afterwards. I'm not sure which was left or right here but the sub unequalized is purple, the response without subs of the center is in black, and the center is still blue. I will think about the DCX2496. I should be getting some tax return money sometime soon.

edit: now getting 98dB in Jurrasic park and the room sounds alright, bit loud though.

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thewire

Discussion Starter · #28 · Feb 6, 2009

Andysu said:
Afternoon Wire, Its chilly here in UK! We had mild snow fall this afternoon yippy![BANANA][/BANANA]

I’d think hard if I was you. I was gutted when I saw the dbx4800 layout at the Empire Leicester Square and know this was the new word for cinema installation. I know there was no sure way I had £3K for each dbx4800 and was I depressed for weeks after hearing it in action with Transformers at 56KW!

After looking around Google I stumbled onto the DCX2496 and when I saw the price I know this would tackle some of the minor difficulties that I’ve faced over the years. Something that has most the problem solving under one lid.

It might have a few things less then the THX dbx4800 but it’s really for cinema the home doesn’t really need it unless you shamelessly rich.

A DEQ2496 is another thing on the shopping list the DCX2496 only has 9 band EQ per LF and HF when used for LCR fronts over its 1, 2, 3, 4, 5 and 6 outputs the more steeper crossover filters you use, the less and lesser the FREE SPACE because on the DCX2496 for dynamic EQ on inputs and all 6 outputs.

But when you weigh the cost of a few DCX2496 two is basic for LCR and another for surrounds and LFE.1 or surrounds and centre back.

Additional ones can be assigned for multiple surrounds and surrounds means lots placed along the walls to warp it around and defuse the sound without the THX being turned ON!

Mine has been turned OFF now for 4 or 5 months. The THX for the surrounds right adds this annoying hand-sawing like sound! That is noticeable with pink noise all-channels it sticks out like sore thumb!

I use 10 surrounds small JBL control 1, six for the sidewalls 3 on each side. 4 on the back wall because two isn’t enough I can hear the gap between the two.

Empire has at least I think 16 on the back wall? 11 for each side wall and each one is powered separately, I think, or that is what I have read, unless two or three are wired together and sent off to the Crown amp and so and so on.

Anyway I can ramble on for hours, a DCX and DEQ is cheap as biscuits when compared to £$3K.

I’d keep working on the graph a simple solution might just be eluding you?

Try standing the sub, on stool, first test it as is, then on a stool in the same area except it won’t be in the space anymore!?

3-D
Forwards backwards
Side-to-side
Up-and-down

I put all these holes in my stage now and the front left and right speakers now match seemless, but there is still the back wall I need to treat. There is the scene in Jurrasic Park right before Dennis is going to execute his virus on the computer, then they cut to the lawyer and the lightning strikes. That boom reverberates off my back wall like it is so easy to make my room sound bad, when in fact it sounds pretty good already. It doesn't sound like when I heard it at the theater I liked so much for that sound, and it is similar to problems I hear. So I want to fix the basics and get rid of the boominess in my room and then I will think about the eq more. :scratchhead: When I get the eq wrong it just sounds worse than no eq at all, and setting up my current eq with the FBQ takes me a long time to enter in the two filters because I feel like I have to get it just right for all four subs and every seat.

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thewire

Discussion Starter · #29 · Mar 2, 2009

Andysu said:
Afternoon Wire, Its chilly here in UK! We had mild snow fall this afternoon yippy![BANANA][/BANANA]

I’d think hard if I was you. I was gutted when I saw the dbx4800 layout at the Empire Leicester Square and know this was the new word for cinema installation. I know there was no sure way I had £3K for each dbx4800 and was I depressed for weeks after hearing it in action with Transformers at 56KW!

After looking around Google I stumbled onto the DCX2496 and when I saw the price I know this would tackle some of the minor difficulties that I’ve faced over the years. Something that has most the problem solving under one lid.

It might have a few things less then the THX dbx4800 but it’s really for cinema the home doesn’t really need it unless you shamelessly rich.

A DEQ2496 is another thing on the shopping list the DCX2496 only has 9 band EQ per LF and HF when used for LCR fronts over its 1, 2, 3, 4, 5 and 6 outputs the more steeper crossover filters you use, the less and lesser the FREE SPACE because on the DCX2496 for dynamic EQ on inputs and all 6 outputs.

But when you weigh the cost of a few DCX2496 two is basic for LCR and another for surrounds and LFE.1 or surrounds and centre back.

Additional ones can be assigned for multiple surrounds and surrounds means lots placed along the walls to warp it around and defuse the sound without the THX being turned ON!

Mine has been turned OFF now for 4 or 5 months. The THX for the surrounds right adds this annoying hand-sawing like sound! That is noticeable with pink noise all-channels it sticks out like sore thumb!

I use 10 surrounds small JBL control 1, six for the sidewalls 3 on each side. 4 on the back wall because two isn’t enough I can hear the gap between the two.

Empire has at least I think 16 on the back wall? 11 for each side wall and each one is powered separately, I think, or that is what I have read, unless two or three are wired together and sent off to the Crown amp and so and so on.

Anyway I can ramble on for hours, a DCX and DEQ is cheap as biscuits when compared to £$3K.

I’d keep working on the graph a simple solution might just be eluding you?

Try standing the sub, on stool, first test it as is, then on a stool in the same area except it won’t be in the space anymore!?

3-D
Forwards backwards
Side-to-side
Up-and-down

The used equalizers are sure as not as cheap as they used to be. I spent awhile trying to find one, then gave up. I did find a cheap subsonic filter to try adding to the subwoofers.

http://store.hlabs.com/pk4/store.pl?view_product=12

Adding lots of acoustic treatments seems to have smoothed out (fixed???) some of the problems. The lower ports on the speakers had been eluding me. :yes:

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