Does Phase Distortion/Shift Matter in Audio? (no*)

[levimax]

I need a good course in Room Corrections Made with an Umbrella LOL

If the speakers are "good" anechoic (FR, directivity, etc) then room EQ should not be much more than knocking down the peaks below Schroeder at the LP. At least that is a good and safe place to start.

 

[gnarly]

If the speakers are "good" anechoic (FR, directivity, etc) then room EQ should not be much more than knocking down the peaks below Schroeder at the LP. At least that is a good and safe place to start.

Thanks, and yep. That's all I've done for many years, electrically.
Otherwise, my 'room tuning' has just been speaker placements, furnishings, a few treatments, etc.......iow, acoustic solutions for acoustic issues.

I did purchase Dirac Live recently to see how it works/what it does.
Ran the full-range stereo setup routine a few times till I got comfortable with it. Never really heard much if any change.

Then i made electrical transfer functions of the processing it had come up with....this is what I was really interested in, much more than what it might do soundwise.
By electrical, I mean the line-level processing, not the speakers' acoustic outputs.
Appeared to leave the left side pretty much alone both mag and phase. And use some maximum phase correction on the right side's low-frequency/sub output, with very little mag correction.
Dirac's way to EQ my particular rig below Schroeder, at LP, I guess.

Anyway, turned it off....maybe to revisit again someday, after I learn a bit more.

 

[mitchco]

Speakers in rooms???
What to correct and how? ....along with equally important knowing what cannot be corrected....is the name of the game, imo.

Have you looked at @j_j 's presentation (download the PPT) on Acoustic and Psychoacoustic Issues in Room Correction.

As far as how, one (bigger than I thought) issue is DSP/DRC tool selection. There are so many products on the market, many with little technical explanation on how they work. In my testing of over a dozen of these DSP/DRC tools, most produced OK results with a few going backwards and taking the life out of the bass dynamics. I was surprised by the range of variability as to the quality of the room analysis algorithms used and the filters these tools design and generated. Out of the dozen or so products I tested (with more yet to be tested) only four produced the results that met my design criteria (as explained in the video linked below).

As an audio DSP programmer from the music production world, I come at this a bit differently. Just like how one can model electronics, guitar cabinets, etc., in DSP, one can do the same for a loudspeaker in a room (i.e. frequency and phase, not directivity). In this video, I explain what to correct, what not to correct, per j_j's presentation. Concepts of breaking up the room into acoustic zones and how room correction applied in each zone is different and why. Concepts around frequency dependent windowing and why it is so important in DRC. Think of how the Klippel scanner works; windows out low frequency reflections to get the direct sound, generally (good) DRC DSP does the opposite and windows out mid to high frequency reflections for a semi-anechoic response as we are mainly focused on the low frequency response of the room and loudspeaker).

As this thread demonstrates, lots of people have experience with phase differences relating to auditory differences, and someone like @KSTR ;-) should really do a video summing up both theory and with listening examples.

This is what we need more of. Listening examples. In this video, I compare three DRC FIR filters that have been designed for a stereo triamp system:

1. Minimum phase room correction with minimum phase digital crossovers
2. Minimum phase room correction with linear phase digital crossovers and driver time alignment
3. Minimum phase plus non-minimum phase room correction with linear phase digital crossovers and driver time alignment

I marked the spot in the video where the comparison starts. The convolver level matches the filters and provides instant switching, even with filters that have inherent delay. Over YouTube, I can hear differences (use headphones - of course these filters were designed for specific speakers in a specific room, so the frequency response "correction" does not apply to whatever you are listening to the audio with - nor does what sounds like preringing which is a digital double bass array working, but no room ;-).
I wonder how many folks hear the same as I do?

Unfortunately, there is no easy way to capture the 3D space of the speakers in the room. I do have binaural mics and made speaker comparison recordings before, but I did not have time to set this up and capture with the binaural mics. I am also looking for a better way... suggestions welcome. So one is only getting the (summed) convolved with music digital output with no acoustic space. Even though the differences are audible, it does not convey the in the room sound field differences, subjectively going from an opaque two dimensional sound (i.e. Filterset1) to a well defined 3 dimensional sound field with a solid phantom center image and clear/dynamic sounding bass that sits in the pocket. I.e. Filterset 3.

Anyone have other listening examples?

 

[levimax]

This is what we need more of. Listening examples. In this video, I compare three DRC FIR filters that have been designed for a stereo triamp system:

1. Minimum phase room correction with minimum phase digital crossovers
2. Minimum phase room correction with linear phase digital crossovers and driver time alignment
3. Minimum phase plus non-minimum phase room correction with linear phase digital crossovers and driver time alignment

Thanks for a great post and great links. Do you have a preference for one of these combinations? Do other people that got to listen to this in the room have a consistent preference?

 

[312elements]

Have you looked at @j_j 's presentation (download the PPT) on Acoustic and Psychoacoustic Issues in Room Correction.

As far as how, one (bigger than I thought) issue is DSP/DRC tool selection. There are so many products on the market, many with little technical explanation on how they work. In my testing of over a dozen of these DSP/DRC tools, most produced OK results with a few going backwards and taking the life out of the bass dynamics. I was surprised by the range of variability as to the quality of the room analysis algorithms used and the filters these tools design and generated. Out of the dozen or so products I tested (with more yet to be tested) only four produced the results that met my design criteria (as explained in the video linked below).

As an audio DSP programmer from the music production world, I come at this a bit differently. Just like how one can model electronics, guitar cabinets, etc., in DSP, one can do the same for a loudspeaker in a room (i.e. frequency and phase, not directivity). In this video, I explain what to correct, what not to correct, per j_j's presentation. Concepts of breaking up the room into acoustic zones and how room correction applied in each zone is different and why. Concepts around frequency dependent windowing and why it is so important in DRC. Think of how the Klippel scanner works; windows out low frequency reflections to get the direct sound, generally (good) DRC DSP does the opposite and windows out mid to high frequency reflections for a semi-anechoic response as we are mainly focused on the low frequency response of the room and loudspeaker).



This is what we need more of. Listening examples. In this video, I compare three DRC FIR filters that have been designed for a stereo triamp system:

1. Minimum phase room correction with minimum phase digital crossovers
2. Minimum phase room correction with linear phase digital crossovers and driver time alignment
3. Minimum phase plus non-minimum phase room correction with linear phase digital crossovers and driver time alignment

I marked the spot in the video where the comparison starts. The convolver level matches the filters and provides instant switching, even with filters that have inherent delay. Over YouTube, I can hear differences (use headphones - of course these filters were designed for specific speakers in a specific room, so the frequency response "correction" does not apply to whatever you are listening to the audio with - nor does what sounds like preringing which is a digital double bass array working, but no room ;-).
I wonder how many folks hear the same as I do?

Unfortunately, there is no easy way to capture the 3D space of the speakers in the room. I do have binaural mics and made speaker comparison recordings before, but I did not have time to set this up and capture with the binaural mics. I am also looking for a better way... suggestions welcome. So one is only getting the (summed) convolved with music digital output with no acoustic space. Even though the differences are audible, it does not convey the in the room sound field differences, subjectively going from an opaque two dimensional sound (i.e. Filterset1) to a well defined 3 dimensional sound field with a solid phantom center image and clear/dynamic sounding bass that sits in the pocket. I.e. Filterset 3.

Anyone have other listening examples?

Hey Mitch, thanks for posting the link. I actually got a lot more out of your other video, “

Understanding the State of the Art of Digital Room Correction”​

For what it’s worth, and I doubt that I’m alone in this, but I really appreciated the step by step process and the suggestions you made regarding rules for what to do and how to do it. Like most, I assume, I’m far more concerned with getting the most out of my system and enjoying the music than understanding the theory behind it. I think for the majority of us, we learn a little bit of theory as we go and it becomes cumulative knowledge. Most tutorials I’ve watched and a lot of the experts on the internet seem to be more interested in flexing their knowledge than actually helping people. A suggestion, if I may be so bold… should you ever create another video on another software program, create a 15 minute version featuring your process with whatever the latest and greatest software tool is. Maybe something like HLC? Forget about teaching anyone anything other than your process in said video. It’s not that the excess information isn’t important, it’s just not the right time to overwhelm people with theory. I think that there are a lot of people that would invest their time and money in better room correction if they didn’t have the obstacle of knowledge placed between their speakers and better sound. Again, the why is important but less important than the how. At least when we’re talking about those of us who do this as a hobby. Once we understand the how, we can always come to forums like this and ask why. Thanks again for the great video. It was enough to make me think this is worth trying to figure out.

 

[gnarly]

Have you looked at @j_j 's presentation (download the PPT) on Acoustic and Psychoacoustic Issues in Room Correction.

As far as how, one (bigger than I thought) issue is DSP/DRC tool selection. There are so many products on the market, many with little technical explanation on how they work. In my testing of over a dozen of these DSP/DRC tools, most produced OK results with a few going backwards and taking the life out of the bass dynamics. I was surprised by the range of variability as to the quality of the room analysis algorithms used and the filters these tools design and generated. Out of the dozen or so products I tested (with more yet to be tested) only four produced the results that met my design criteria (as explained in the video linked below).

As an audio DSP programmer from the music production world, I come at this a bit differently. Just like how one can model electronics, guitar cabinets, etc., in DSP, one can do the same for a loudspeaker in a room (i.e. frequency and phase, not directivity). In this video, I explain what to correct, what not to correct, per j_j's presentation. Concepts of breaking up the room into acoustic zones and how room correction applied in each zone is different and why. Concepts around frequency dependent windowing and why it is so important in DRC. Think of how the Klippel scanner works; windows out low frequency reflections to get the direct sound, generally (good) DRC DSP does the opposite and windows out mid to high frequency reflections for a semi-anechoic response as we are mainly focused on the low frequency response of the room and loudspeaker).

Hi Mitch, thanks for the reply. I think you are probably the most experienced person I know of, in terms of one who works with room corrections.

Yes, I'm familiar with the j.j. presentation you linked. I just reread it, and other than some of the details in the second Sequence of Operations section, it's stuff I've absorbed pretty well I think. Breaking the room into zones makes easy sense. So does frequency dependent windowing/solutions...certainly if one is trying to use global type corrections.
Since I avoid global corrections like the covid, never had to worry about that one Lol

What I'm really looking for, is not the best DSP/DRC tool out there, not in terms of its automated capability.
I look for the best tools in terms of manual capability that let me explore and make roll-my-own tunings/corrections.
If anything, I'm after the best indoor measurements i can make. Particularly with subs/bass. I know how hard it is for FFT/IFT to give good repeatable low freq data....I have a hard time believing the legitimacy of most low freq measurement post i see. Anyway, gonna read Sequence of Operations again.

Biggest issue, when I look at myself as honestly as i can, I realize I just need to get serious about even wanting room tuning.
I'm am about as far away from a seated sweet-spot listener as one can get, my speakers on subs are all on castor wheels, and they are constantly changing as I DIY experiment....and.....i still hear the most glorious sound I've ever heard from outdoor setups ! Hard to get the room thingy motivation going.
But I digress badly...this is a thread about phase.

 

[j_j]

As to locating the locations of speakers, there's a paper in the AES convention record by "Johnston and Fezjo" (not sure which order), maybe with some other authors, too. It's been a while, but it is possible to capture such information and get proper timings pretty easily. Even the tiny room correction in Windows 7, 10, and 11 (dig deep deep deep into the audio tools in the driver level, you'll find it) will do an extraordinarily good job of time EQ, btw. The interface, last time I tried it, was busted. You need stop and start the audio server in order to sort that, sometimes. If it refuses to get a stable solution, that's the problem.

Yes, Serge Smirnov and I wrote that one.