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Is Dirac mistake ?


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Hello,

 

I would like to know if I must to worry about the following differences between Dirac curves and Rew curves of my right front channel response.

For my untrained eye, the right speaker response in the lower frequencies around the roll-off (45hz) with DiracFront right dirac.PNG

is very different than with Rew. (all variables other than software remain constant: mic position, speaker set-up etc)Front right rew.jpg

 

For me untrained eye there is no such a difference with the left speaker

left front rew.jpg

 

I am afraid that the calibration of the right channel by Dirac will not be good because of this difference. Also, I ask to myself if I have a software problem and should uninstall and reinstal dirac ?

 

I should have added that I switched speakers (right to left position and vis-versa) to see if it was a speaker problem and I got the same readings. Is it the signal into the right channel path that is different?

left front dirac.PNG

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The two sets of measurement curves should be approximately the same (both for L vs. R and for Dirac vs. REW). Either there is a problem with Dirac or there is a problem with a crossover being applied somehow in one case but not the other (or maybe your sub is only using one of the two channels or something weird like that, but why would this only show up with Dirac?). (Do both REW and Dirac use exactly the same signal path?)

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Hello,

 

I would like to know if I must to worry about the following differences between Dirac curves and Rew curves of my right front channel response.

For my untrained eye, the right speaker response in the lower frequencies around the roll-off (45hz) with Dirac[ATTACH=CONFIG]24367[/ATTACH]

is very different than with Rew. (all variables other than software remain constant: mic position, speaker set-up etc)[ATTACH=CONFIG]24368[/ATTACH]

 

For me untrained eye there is no such a difference with the left speaker

[ATTACH=CONFIG]24369[/ATTACH][ATTACH=CONFIG]24370[/ATTACH]

 

I am afraid that the calibration of the right channel by Dirac will not be good because of this difference. Also, I ask to myself if I have a software problem and should uninstall and reinstal dirac ?

 

I should have added that I switched speakers (right to left position and vis-versa) to see if it was a speaker problem and I got the same readings. Is it the signal into the right channel path that is different?

 

Chances are you will get different raw measured frequency response curves from Dirac and any other tool, like REW. Dirac uses a sophisticated average of multiple mike positions, and probably your REW curve is just one position. Also, the mike positions are probably not the same between the two separate sets of measurements. Since room response varies by mike position, often by quite a bit, it is very difficult to get identical measurements in looking at room acoustics.

 

There may also be other measurement differences between tools, like time windowing, 1/X octave smoothing, etc., which might falsely give the appearance of a different result.

 

I think that Dirac's averaged multi-mike method is a more accurate indicator of what you hear. I do think single point measurements are of very limited use for doing room EQ. Probably, that explains the difference you see. But, sure, if you are worried about it, reload Dirac. However, I think if there were a software corruption issue, you would see a more drastic problem, like an error message or a crash.

 

Bottom line, I think Dirac is giving you the more accurate measurements and EQ. Trying to reconcile REW measurements with Dirac is a confusing waste of time usually. You should not simply assume Dirac is wrong and REW is right.

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The two sets of measurement curves should be approximately the same (both for L vs. R and for Dirac vs. REW). Either there is a problem with Dirac or there is a problem with a crossover being applied somehow in one case but not the other (or maybe your sub is only using one of the two channels or something weird like that, but why would this only show up with Dirac?). (Do both REW and Dirac use exactly the same signal path?)

 

Thanks for your response. I should have been more detailed in my infos.

I might add that the path between Rew and Dirac is different. I use NanoAvr-DL. With Rew, the signal goes from laptop to hdmi to video3 input in the receiver. Dirac signal goes from the sofware or the nano I do not know via hdmi and continue into the receiver via video1 input.

But the left signal is correct in those 2 cases. Not the right. The sub signal goes out the receiver via rca preout sub to left rca "LFE" in (SVS PC-2000). Again, I don't think that it is the problem : left is similar, not right.

I can add also that the center and the surronds are similar between Rew and Dirac.

 

Also I tried with only one round of sweep with Dirac as Rew does, and the curves were the same as those I downloaded here.

 

Also in all the cases, receiver was set to "no eq" speakers set to large, no sub or sub off (so no xover) because I wanted to get a set of filters for music only.

When I did Dirac measuremnts for my 5.1 set-up, left and right curves was similar to Rew with bass management active. It is logial because NanoAVR-DL asked for bass managed into the receiver.

 

So my difficulty is for stereo calibration.

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the path between Rew and Dirac is different.

...

 

The sub signal goes out the receiver via rca preout sub to left rca "LFE" in (SVS PC-2000). Again, I don't think that it is the problem : left is similar, not right.

 

I think this has to be the source of the problem, one way or another.

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His left speaker measures the same with Dirac and REW, which is therefore a positive control. I can buy small differences, but the right speaker looks like a crossover was applied to filter out content below 100Hz.

 

I agree - that right speaker response looks very much like a crossover is still being applied. I don't know why it doesn't happen with REW? FWIW I checked the Dirac response with both REW & Fuzzmeasure in my setup and was impressed with how all the curves were very much identical.

 

Perhaps you should post this on the MiniDSP support forum....

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I agree - that right speaker response looks very much like a crossover is still being applied. I don't know why it doesn't happen with REW? FWIW I checked the Dirac response with both REW & Fuzzmeasure in my setup and was impressed with how all the curves were very much identical.

 

Perhaps you should post this on the MiniDSP support forum....

 

I did not think to the kind of xover thing. If it is, it is bizarre because for my stereo filters with Dirac I setted the speakers (before the first measurements) in the receiver like this: center none, surround left none, surroun right none, sub none.

 

I asked today the same question on the Minidsp Forum.

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There is something the receiver is doing to one channel but not the other because the sub is plugged into the left channel.

 

I'm not sure if the crossover is being applied on the left and right symmetrically, and there is only bass signal in the left channel, but I am almost certain that this is the cause of the anomaly.

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The sub is plug to to LFE channel into the back panel of the sub . There is no such a left channel output in the receiver. I have 2 sub out in the receiver for 2 subs but I only use one sub. So I do not think that the reciever send a kind of LP or HP filter to the right channel only to the sub.

Maybe flak is reading this thread and could gives some thoughts ?

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The sub signal goes out the receiver via rca preout sub to left rca "LFE" in (SVS PC-2000)..

 

Pre-out and LFE out are two different things. The receiver might have the ability to toggle what goes out the RCA. Why not do some experiments? What happens when you use the same signal path but remove Dirac from the chain?

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I have done the following test. First I ran a sweep with Dirac to my fronts speakers with standard connection. NanoAvr-DL was set to stereo, Dirac cal.tool was set to stereo and no sub, all settings in the receiver was set like 2 channels only, no internal EQ, no sub, no xover...name it = dead flat stereo system. I got hte same fault into right channel curve by Dirac. Then I connected my laptop to NanoAVR-DL to get Rew measuring the system via the same path than nano. The fault in the right channel from Dirac was not there with Rew.

 

Secondly, I switched cable connections leaving the speakers at their place. So the right channel of the receiver was connected to left speaker and vis versa. I ran Dirac and the fault into the bass fr switched into the curve of the left speaker i.e. the bad result was now into the curve of the left speaker. I checked with Rew and there was no fault : curve of left channel remains the same and so on for the right channel without any faulty result for bass fr.

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  • 2 weeks later...

Final update.

It seems that the problem was coming from the bluray palyer which is upstream !? (bluray-nano-receiver-display)

It is a mystery for me. I disconnected the receiver and the settop box leaving only laptop-nano-receiver in the chain. And results with Dirac was correct for the right channel. I reconnected the player. I reset bluray ( 3 months old only) to factory default and did one Dirac measure which seemed correct.

 

I can't explain that and why REW was not affected by this.

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