# Phase inversion with DEC2496



## Joppnl (Nov 2, 2010)

Hello,

just started with RoomEQ wizard and a Behringer DEC2496 i see something strange:

The setup is: PC->optical out to DEC2496 --> optical to Yamaha RX-V1700 -> analogue front out on Yamaha to input Behringer 0202 external sound card --> via USB to PC 

1st:
config the i/o on the Behringer to direct connect input -> output:
http://picasaweb.google.com/Jurgenopreis/RoomEQ#5538310949054789074










The strange thing here is that at 1280Hz there is a phase inversion coming from -178 going to 182 so it is 360 degrees

Then I put the input selector so DEq and PEQ are in-line but not active:










http://picasaweb.google.com/Jurgenopreis/RoomEQ#5538310957192745330

This looks perfect: it's the same figure as without the Behringer in the optical signal.

Then at 1kHz I made the GEQ acitve:










http://picasaweb.google.com/Jurgenopreis/RoomEQ#5538310957358861762

Same as direct i/o"a phase shift occurs, also 360 degrees

Then only PEQ on 2 diff freq:










http://picasaweb.google.com/Jurgenopreis/RoomEQ#5538310952010540018

As you can see: each time the PEQ becomes active a phase shift will occur.

My question is: what do the phase inversion do with the audiosignal: will it 'damage' the audiosignal, am I able to hear it?

Should it be a reason not to put the DEC2496 in the optical audio-path?


Thanks!


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## Wayne A. Pflughaupt (Apr 13, 2006)

Welcome to the Forum, Joppnl!


> My question is: what do the phase inversion do with the audiosignal: will it 'damage' the audiosignal, am I able to hear it?


No. Phase shift is part and parcel to equalization. In fact, I’ve seen it argued that phase shift is the reason you hear an audible effect from equalization. Regardless, any potential phase shift from the EQ pales in comparison to the phase shift you’ll get once the sound leaves the speakers and bounces around the room.


Regards,
Wayne


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## Joppnl (Nov 2, 2010)

Thank you for your welcome-word and your answer Wayne.

Just 2 graphs what I achieved tonight with the DEC2496 tonight.

Setup: as said above, speakers Infinity overture 2 (active bas)

Sweep, room analysis Without correction:









http://picasaweb.google.com/Jurgenopreis/RoomEQ#5538408133212491986

As you can see: the mid's and highs have a lot of going up-down.

On 48 Hz there is a huge bass-peak

After the 48Hz correction (only 4 PEQ filters active around this freq):

http://picasaweb.google.com/Jurgenopreis/RoomEQ#5538408138908718978


Wow!! What we see is that the peak on 48Hz is more flattened but also the mid and high is a better graph. 

Very strange because I did not do any eq in this freq area (so how could this happen?)

And then, are we able to hear it.

Testsong: Crosby & Nash same named album : I surrender

This song has some very low bass-notes.

After the first bas notes it's already clear: the bass is at a much more constant level. The resonance peak visable in the first graph and audible in this song has disappeared and is at the same level as the others.

More then that: around 1min20 the bass goes very low. This very low bass-note wasn't audible before, now it is!

It is as if there is a much higher priced amp playing now!!

What would you advise if you see the 2nd graph: any more corrections?

ps: I'm not able to put graphs in my post (with the


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## Wayne A. Pflughaupt (Apr 13, 2006)

Yes, 5 posts are needed before you can use the IMG tags. However, you can upload graphs directly to your posts – click “Go Advanced,” then scroll down to “Manage Attachments.”

Regards,
Wayne


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## Wayne A. Pflughaupt (Apr 13, 2006)

> What would you advise if you see the 2nd graph: any more corrections?


Depends. What mic are you taking the measurements with, and is there a calibration file?

Regards,
Wayne


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## Joppnl (Nov 2, 2010)

again, thank you for your help Wayne.

The mic is the RadioShack dB meter together with the correction file as found here in the download section.

What I read is that above 3kHz the meter isn't good anymore.

Do you think the Behringer ECM8000 whould be helpful in getting a better room correction as room correction is advised to do only in the low-freq area (as I read but may-be not?)

but if you read the 2nd graph would you correct it?

May-be if I buy the mic I can do a RTA with the FBQ2496 from 100Hz up and adjust below 100Hz manually, good idea?


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## JohnM (Apr 11, 2006)

Joppnl said:


> The strange thing here is that at 1280Hz there is a phase inversion coming from -178 going to 182 so it is 360 degrees


There is no phase inversion happening at 1280Hz, just a phase wrap. Phase is plotted "wrapped" to span 360 degrees, this sequence of phase values has 1 degree changes: -178, -179, 180, 179, 178, 177. -180 and 180 are actually the same point, this is more easily seen if you use the control panel and unwrap the phase so it is allowed to continue its downward trend past -180 to -181 etc rather than wrapping. The reason you see this is somewhere in the overall chain of devices there is an inversion (or some series of an odd number of inversions), inversion is 180 degrees of phase shift so rather than the phase trace running along close to zero it is close to -180/180, a tiny change in phase will result in a line being drawn on the graph to join the wrap points, but it is still just a tiny shift in phase. You can tell REW in the soundcard settings that the path is inverting and it will re-invert the measurements for you.


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## Joppnl (Nov 2, 2010)

well John,

thank you for your wonderful explanation.

I tried the unwrap option and the 'inversion' (what it isn't as you explain) disappears.

Some new pics:

without room correction :

http://picasaweb.google.com/Jurgenopreis/RoomEQ#5538779678080325986










with room correction up to 115Hz:

http://picasaweb.google.com/Jurgenopreis/RoomEQ#5538779691338262082











Especially the peaks in the bass-section (left of the blue line) are much more better. And not only it looks better, it sounds better as well!

One remark: the Behringer DEQ2496 is not on the list of eq's.

if I pick the FBQ2496 RoomEQWizard gives me instructions on the parametric eq's I can not do with the deq2496.

Is it possible to implement the DEQ (ultra-curve pro) 2496?


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## JohnM (Apr 11, 2006)

Joppnl said:


> Is it possible to implement the DEQ (ultra-curve pro) 2496?


It is on the (long) list of things to do


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## Joppnl (Nov 2, 2010)

Well, thank you in advance (but a big thank you for developping the software as it is now, it's a great tool (although i have to learn a lot))

I think the DEQ is almost the same as the FBQ2496 only the max gain per filter is +/-15dB amd there are max 10 filters.

Frequencies are almost the same: if the FBQ says i.e. 97.07 the DEQ has 97.1

One more question if I may : When RoomEQWiz automatic eq comes up with a boost of let's say +9 dB on an bass-freq (<100hz) to get the curve as you want it to be would you advise to set it or would that probably damage the speaker?

thnx


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## Wayne A. Pflughaupt (Apr 13, 2006)

> When RoomEQWiz automatic eq comes up with a boost of let's say +9 dB on an bass-freq (<100hz) to get the curve as you want it to be would you advise to set it or would that probably damage the speaker?


Obviously the amplifier and/or speaker would reach maximum capabilities at that frequency sooner. It’s probably academic, though. Any equalization is going to create peaks and valleys in response, even if you only cut, and the high areas will tax the amp or speaker before the low areas. There’s no free lunch with equalization. If you don’t have ample headroom going in, you shouldn’t do it. More detail on boosting vs. cutting here .

Regards,
Wayne


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## JohnM (Apr 11, 2006)

Joppnl said:


> One more question if I may : When RoomEQWiz automatic eq comes up with a boost of let's say +9 dB on an bass-freq (<100hz) to get the curve as you want it to be would you advise to set it or would that probably damage the speaker?


The key question is whether that refers to an individual filter or the overall effect of all the filters at some frequency. If the overall effect produces no boost there is no loss of headroom even if individual filters have significant boost, this could arise if a filter is being used to compensate for the reduction in level caused by other filters that are being used to cut peaks. Use the EQ panel's overall boost limit to stop excessive overall boost being applied.


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## Joppnl (Nov 2, 2010)

First a word of thanks to all who replied to my questions, for now all my questions are answered and I'm going to read a lot and, not forget, to enjoy listening to music.



JohnM said:


> Use the EQ panel's overall boost limit to stop excessive overall boost being applied.


Good thing.....I can check that easy by watching the dB level on the Behringer As I watch it now I see sometimes the red lights of the VUmeter light up so i will adjust the overall gane of the eq in the utility setup.

Bye, thanks again,


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## cast55 (Dec 30, 2010)

I read somewhere that there was a bug in an earlier version of the DEQ2496 firmware which had something to do with a phase issue. I've been searching for the exact article but I can't seem to find it now. Anyway, the latest versions of firmware are 1.4 for version 1 hardware, and 2.5 for version 2 hardware. If you are not running the latest firmware for your unit, you might want to update and measure again to see if anything changes.


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