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Pre-ringing with linear phase room EQ filters

Krunok

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#1
For quite some time I was using minimum phase room EQ filters tha I generated mannually with rePhase, but recently I decided to apply full scale time domain correction and go for linear phase response. As a result I got pretty nice looking phase, GD and step response graphs (measured at LP, 4m away from speakers):

Phase.JPG


GD.JPG


Step.JPG


As a side effect I also got some pre-ringing in my filters which is visible in IR:

Left
Left.JPG


Right
Right.JPG


That pre-ringing visible before IR got me worried a little, especially as I was not able to find any relevant data on the Netabout audibility of pre-ringing artefact. And no, I cannot hear any nasty effects after I adjusted phase - subjectively I would say sound got better, but of course it's impossible to tell that without a proper blind test.

Anyway, what I did found was an IR response of Topping D10 posted on this forum:

Topping D10 IR.png


What surprised me is how similar it looks to IR of my speakers, both in terms of shape and in terms of pre-ringing. Based on that my conclusion was that pre-ringing with my room EQ filters is very acceptable, so nothing to fear off.

What are your thoughts/comments on this? :)
 

daftcombo

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#2
For quite some time I was using minimum phase room EQ filters tha I generated mannually with rePhase, but recently I decided to apply full scale time domain correction and go for linear phase response. As a result I got pretty nice looking phase, GD and step response graphs (measured at LP, 4m away from speakers):

View attachment 47650

View attachment 47651

View attachment 47652

As a side effect I also got some pre-ringing in my filters which is visible in IR:

Left
View attachment 47654

Right
View attachment 47655

That pre-ringing visible before IR got me worried a little, especially as I was not able to find any relevant data on the Netabout audibility of pre-ringing artefact. And no, I cannot hear any nasty effects after I adjusted phase - subjectively I would say sound got better, but of course it's impossible to tell that without a proper blind test.

Anyway, what I did found was an IR response of Topping D10 posted on this forum:

View attachment 47657

What surprised me is how similar it looks to IR of my speakers, both in terms of shape and in terms of pre-ringing. Based on that my conclusion was that pre-ringing with my room EQ filters is very acceptable, so nothing to fear off.

What are your thoughts/comments on this? :)
The last graph looks like the one I posted a few months ago. :)

I can't hear the difference between linear phase & minimum phase filters when EQing neither.

Pretty clean impulse you got with your speakers by the way.
 
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Krunok

Krunok

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Thread Starter #3
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Krunok

Krunok

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A sharp cut in the audible range using a linear phase filter can cause perceptible "ringing." A minimum phase filter still has ringing, of course, but it is more readily masked by the main sound. If your adjustments are not too steep or too deep, you can probably safely use linear phase filters.
That part is clear to me, but what I find problmeatic is that there seems to be no "metric" to say what is acceptible and what is not in terms of filter's pre-ringing.
For example, can you tell by looking at IR of my speakers if I can expect to hear pre-ringing or not?
Am I on the safe side as IRs of my speakers don't have much more pre-ringing than my Topping D10 DAC?
 

UliBru

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#6
An ideal speaker will show up a minimumphase behaviour. It simply behaves causal = no output when no input.
With typical passive crossovers beside minimum phase the speaker will show up an excess phase which contains delays.

A correction filter for minimum phase (=frequency response correction) is itself minimum phase.
A correction filter for excess phase (= time correction) will introduce a pre-ringing.
A pre-ringing is allowed as long as the corrected step response does not show up a pre-ringing or if the pre-ringing is small enough. So pre-ringing is simply allowed if you don't recognize it.
If there is too much pre-ringing you will recognize it. So e.g. a simple drum hit = tok may sound like whoop-tok.

If you like to get an example of pre-ringing you can send me measured pulse responses and a flac-file by PM.
 
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Krunok

Krunok

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Thread Starter #7
An ideal speaker will show up a minimumphase behaviour. It simply behaves causal = no output when no input.
With typical passive crossovers beside minimum phase the speaker will show up an excess phase which contains delays.

A correction filter for minimum phase (=frequency response correction) is itself minimum phase.
A correction filter for excess phase (= time correction) will introduce a pre-ringing.
A pre-ringing is allowed as long as the corrected step response does not show up a pre-ringing or if the pre-ringing is small enough. So pre-ringing is simply allowed if you don't recognize it.
If there is too much pre-ringing you will recognize it. So e.g. a simple drum hit = tok may sound like whoop-tok.

If you like to get an example of pre-ringing you can send me measured pulse responses and a flac-file by PM.
Thank you very much Dr. Brüggemann, PM sent!
 

NTK

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#8
You can see that the ringing frequency is about ~20 kHz (~2 cycles every 100 μs). Theoretically it should be the Nyquist frequency. If you look at the Topping response, it rings at very close to 22.05 kHz, and matches very well to the theory.
 
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Krunok

Krunok

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You can see that the ringing frequency is about ~20 kHz (~2 cycles every 100 μs). Theoretically it should be the Nyquist frequency. If you look at the Topping response, it rings at very close to 22.1 kHz, and matches very well to the theory.
True, but green curve (left channel) has some ripples of pre-ringing that are 1 cycle per 100μs. Or you think they are of too small amplitude to be problematic?
 

NTK

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True, but green curve (left channel) has some ripples of pre-ringing that are 1 cycle per 100μs. Or you think they are of too small amplitude to be problematic?
Sorry. I have no idea. However, music isn't impulses. The impulse response may offend the eyes, but not necessarily the ears :)
 
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Krunok

Krunok

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Sorry. I have no idea. However, music isn't impulses. The impulse response may offend the eyes, but not necessarily the ears :)
Well, to be honest, as my impulse responses are looking quite similar to the D10 impulse response I am trying not to be worried. :)
 
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Krunok

Krunok

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Dr. Brüggemann (aka @UliBru ) has kindly shared this music sample which contains 4 drum kicks without pre-ringing and 4 drum kicks with pre-ringing, so give it a try!
 
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solderdude

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#13
linky no worky.
Links to: http://www.brüggemann.com/ with a 404 error notification (im Deutsch)
 
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Krunok

Krunok

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Thread Starter #18
It would be interesting though to see difference in spectrum, as I suspect it exists. There is always a price to be paid so I suspect pre-ringing reduction also comes with a price tag. ;)
 
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Krunok

Krunok

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Thread Starter #20
The preringing is caused by an "excessive" excessphase treatment.
I can hear the difference with my speakers but only without my roomEQ filters. I can't hear it with them which means they probably have too much pre-ringing so they're covering the difference, which means my excessphase treatment was obviously "excessive". :D

Dr. Brüggemann, once again I thank you for your kind assistance!

And tommorow..
Capture.JPG
 
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