A SMAART Question......it's about phase

[dumdum]

I wish I could chime in helpfully here... but I can't.
I'm going to be playing with my first AP filters in my own DSP install, first I've ever personally owned, and first I've taken further than an initial tune - which still isn't complete.

I definitely want to get my hands on SMAART because so SO SO much is hidden invisibly and potentially frustratingly, after you've done your EQ-ing, aligning, and even acoustical interior treatments. I've never had it that tool OR a way to mitigate those issues, so being able to actually MEASURE those phase shifts, apply AP filters, then observe your impact in the phase realm - just awesome.


I suspect your phase anomolies are actually DUE to your crossovers - as the sound rolls off below the high-pass frequency, there is a phase shift, no matter whether you picked bessel or butterworth or linkwitz-riley or anything - in fact that's the reason system designers have historically tried to use as few drivers as possible. Ideally a single point-source driver would most accurately reproduce the sound because it is perfectly phase-correct. Even if you had a mid and tweeter that were theoretically perfectly flat in dB level from 20hz up to 20khz and beyond, you need that crossover point - which even if perfectly aligned so there's no dip in frequency response, it does mess up the phase on both side of the Xover point... for the tweeter, below it, and for the mid, above it.
The steeper the slope, the faster they roll off, but also the faster the phase shift happens.
Traditionally it's been impossible to really correct for this - but it seems like with the right tools and DSP/filters - I mean wow, this really is one of the old-school fundamentals being tackled here.

If - *if* you could actually flatten the frequency response across a crossover point, AND flatten the phase response across the crossover point, you absolutely could dramatically improve your imaging.
I almost typed "to the degree where you emulate that theoretical-ideal point-source driver", but unfortunately the complex reflections in our car interiors would prevent us from QUITE getting to that perfect ideal, since the two drivers do need to be in two different locations in space physically - but maybe it would open the door for systems more like my current install (sub... midbass... midrange... wideband... tweeter... read "way too many Xover points for phase coherence) to be as good as my old-school ideal systems for imaging (sub... 6.5 midbass/midrange... tweeter that can reach from below 2khz to over 20khz). The old school ones WERE difficult to nail imaging particularly right around the Xover point - which had everything to do with this phase shifting, and that's a fascinating aspect of Psychoacoustics...
Consciously, you can't really "listen" for phase.... other than being aware that the image isn't correct. And it's entirely your subconscious recognizing that the sound isn't exactly correct. It's completely what led me to be fascinated with the very concept of imaging.
Still - what a tool, so effing cool... At least to a geek like me.

you can listen for phase… do your eq and make sure both sides sound the same to your ears (not with a mic)

if they don’t the eq and rta is telling white lies… purely because we hear differently to how a mic reads that picks up everything…

anyway… you want to know how to sanity check your left right time alignment is correct (a mic tip doesn’t quite replicate a set of ears 5-6” apart with head related transfer function) so play music… any music, well recorded and mastered ideally, now feed left and right into both left and right channels, where should all the information come from? The centre, if the timing is correct all information should be pin point in one spot, you will find when you go to far one way or the other the centre will blur to the left or right and you will hear information coming from the left or right, high frequency information will always move first and snap into the centre last over the lower registers just because the high wave lengths are shorter and it will come into phase and out of phase faster

[geolemon]

you can listen for phase… do your eq and make sure both sides sound the same to your ears

I think you were responding to this:

...that's a fascinating aspect of Psychoacoustics...
Consciously, you can't really "listen" for phase.... other than being aware that the image isn't correct. And it's entirely your subconscious recognizing that the sound isn't exactly correct. It's what led me to be fascinated with the very concept of imaging. .

My point is - you can't "hear" phase, and even the things that you hear, it's your subconscious doing for you.

If you installed a component set, and installed one side out of phase relative to the other (the worst case scenario in most cars), I'm not saying "you can't tell one side is out of phase". I'm saying it's psychoacoustics, your subconscious that's somehow able to compare the two sides of the signal and create that confused, diffused sense of "image" in your head. It's that resulting sense of image that you are responding to. You aren't consciously staring over the dashboard and hood and listening for whether the cymbal hit sounds clear - you are consciously staring over the dashboard sure - hoping for a thing to occur in your subconscious - that illusion of depth and space that makes you doubt your eyeballs. The cymbal hit should be... THERE. A location in space, not just a sound. The sound you can listen for with your ears - the location in space requires you to wait for your subconscious to give you something.

The REW-measurable stuff doesn't really change - you could have a nice, flat-ish EQ curve right across the board, even with one side out of phase, and not miss a note, instrument, word, etc that's contained in the song that you can consciously listen for - but "are you fooled"? That's all subconscious trickery - like a sense of balance.
So this SMAART is one step closer (and I'll have to check out that free one- that's a no-brainer), although it's still in the "reproduce what's in the recording" realm.
I wish there really were a way to directly measure for "imaging". Scientifically there must be - maybe a dummy head with two mics placed inside anatomically correct ears and ear canals measuring phase and response... I'm sure we have the measurement power these days. But can we simulate what your subconscious does?

That also brings me back to one of my fallback points for people who argue that SQ is as simple as "reproducing what's on the recording exactly like the engineer intended":
First off, headphones do that. I've even been playing with in-ear monitors a lot lately (there's lots of inexpensive great ones!), and I have some fancy over-the-ear noise-cancelling cans, and my second set (anniversary edition!) of Koss PortaPro on-ear classic legends...
They all have great detail. And yet none of them "image". There's more to it than just "reproducing the audio signal".
Second off, "like the engineer intended" has it's own can of worms assumptions but that's for another thread.

But I think I'm preaching to the choir, here. You know what I mean, I'm sure.

[dumdum]

And that is my point, our subconscious does things we can’t simulate with a pure measurement sustem, so use your ears for the fine tuning, and I’ve explained a method that you can use, you don’t need to argue how or why we can’t do what we can do as we sure can do it, you just have to set the stereo up to do it, in stereo it’s incredibly hard to hear or find the focus point where it snaps into place, but given certain conditions it gets a lot easier

[Jdunk54nl]

So was talking with Nick Ames (JL Audio) and we had a good conversation as to why phase will bend like this and wrap quickly. He made me have another epiphany moment (every time I talk to him this happens).
So, for all of those other people that want to have an epiphany moment here you go

Think about it this way, the thing that causes the phase to get to a steeper slope is time delay, as in, if I add delay the phase bends down.

So, if all of a sudden there is an area that the phase is bending down, like in the circled part below, that means there is a time delay of that audio.

The speaker didn't suddenly change it's position for that information, so it is not the cause of this. Instead this would be sound arriving later than what the speaker caused...as in..... a reflection! This also means that the reflection was the dominant source of energy if that causes the phase to wrap like that!

Note: This is assuming that you don't have all pass filters that could also cause something like this.

[BigAl205]

Have you tried unwrapping the phase in the options menu? It sometime makes it easier to see what's going on...at least for me.
If the reflection is dominant, and it's not something you can eliminate, should you tune the system to the reflection instead of the driver itself?

[Kevin K]

Yep, make the environment work for you

[Jdunk54nl]

Yes, you should definltely eq the dominant source of energy, but this would be hard to diagnose without being able to view phase in real time that the dominant source of energy is not the speaker but the reflection. The ultimate solution though would be to go back and visit your install and fix the issue if you can.

Also to unwrapping the phase, wrapped vs unwrapped doesn't really matter, you still have that increase slope for a short amount of time due to that dominant energy arriving later from the reflection. I like to just use the "scroll" function on the phase by pressing the up/down arrows on the keyboard to get the zone I am most interested in all in the same screen.

Also remember for this example, it is on the tweeter and not worth really fixing (although I probably still would...because ocd....)

But I did just experience this same thing in a dodge ram 2500 truck that was being tuned on the midrange due to placement issues.

[dumdum]

Have you tried unwrapping the phase in the options menu? It sometime makes it easier to see what's going on...at least for me.
If the reflection is dominant, and it's not something you can eliminate, should you tune the system to the reflection instead of the driver itself?

Unwrapping phase does not display correctly in smaart or in rew, where the phase wraps the following phase trace steps down, even though the next portion of energy is no later, the phase trace will not really be later, the sound at higher freqs won’t arrive a whole wavelength later… you can add an all pass to emulate this and see what that does to the phase trace… it also doesn’t make the freqs above the all pass arrive later despite a wrap making it look like it does ���� the software just interprets the data as it sees it

the late arriving phase data does in fact corrupt the signal to a degree as stated above, and the software displays it as it ‘sees’ it, but unwrapping is not really helpful that I’ve ever seen

[Justin Zazzi]

So was talking with Nick Ames (JL Audio) and we had a good conversation as to why phase will bend like this and wrap quickly. He made me have another epiphany moment (every time I talk to him this happens).

Omg me too!
Every. Single. Time.


Interesting thought about the dominant energy being from a reflection.
I've seen this kinda thing in the phase plots before too, not very often, but it's always a puzzle.