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If the errors in the frequency response are minimum phase to begin with, IIR filters (being also minimum-phase) will correct the phase at the same time as they correct the amplitude response.
If the errors in the frequency response are minimum phase to begin with, IIR filters (being also minimum-phase) will correct the phase at the same time as they correct the amplitude response.
...and in the case of loudspeakers and rooms, the errors tend to be (more or less) minimum-phase.
Does that include nulls when the waves from two sources (stereo) cancel each other at some point in the room?
That's what I have in the 48Hz area at the listening position with the current setup.
I use commercial DSP software like Audiolense and Acourate.
That kind of null will not be fixable with min-phase EQ, no. How are you dealing with it atm?
Does Audiolense work on a mac?
Exactly! Phase distortion is related to the slope of the filter. Use gentle slopes (numerically small Q, wide frequency range) minimizes it.
Question: When the room boosts or cuts certain frequencies, it also induces phase distortion. Could it be possible that the phase distortion of a parametric EQ opposes this, so the filter corrects phase as well as amplitude? If so, a parametric EQ's "side effect" of shifting phase would actually be beneficial!
That kind of null will not be fixable with min-phase EQ, no. How are you dealing with it atm?
Some of the procedures in post 24 show how to average measurements as well, including this tutorial https://www.dropbox.com/s/10xdhh83jokzbxv/REW_rePhase_tuto.pdf?dl=0 which describes the same procedure above.
However, some of the top DSP software packages take a slightly different approach so as to achieve similar results without having to average. The issue is most software simply inverts the magnitude response and is indeed constrained to a single point. Audiolense (which also does multi-seat averaging) and Acourate use a slight different analysis technique to avoid overcorrection:
View attachment 22692
If one studies the chart closely, one can see the envelope response is following the peaks but not the dips. Note the marker at just over 100 Hz., one can see a very narrow dip, but the new analysis does not follow that narrow dip. This new frequency response can be considered as an upper envelop of the original magnitudes. The spectral envelope is used as the basis for further calculations. It even supersedes the need for multi-location measurements in a typical small listening environment like a living room. I have verified this in my book where I took 14 REW measurements across a 6ft x 2ft grid area (where my couch is) and the low frequency response is virtually the same at all 14 points, based on a single analysis measurement used to calculate the correction filter.
Audiolense, pretty much the same, even though it does have an option for multi-seat measurements...
Are you saying that a single sweep when "enveloped" like you have shown above can replace multipoint averaged measurement yielding the same results?
Yes. But it is specific to Acourate and Audiolense as the envelope/psychoacoustic filtering is proprietary for both software packages...
No, both are Windows programs, but I do believe some members run the Designer under Mac's virtual machine, and then use a Mac native convolver to host the FIR correction filters for music playback. Bernt on the Audiolense forum can confirm...
Your system is really impressive and obviously extremely well tuned! Still, I can't find info how you measured the repsones you've shown, so can you please clarify?
I have seen many discussions on this topic, some in favor of measuring bth speakers at the same time to evaluate response up to 300Hz, some saying it's not neccessary. I would very much appreciate if you can find the link and post it , preferrably in the "Room EQ, do's and dont's thread".