If you're talking about this article (Uncanny Sight in the Blind: Scientific American),
these people are blind because of occipital lobe (the primary visual cortex) brain damage, not because of eye damage. Basically, the brain is complicated. As you might surmise from the word "primary," there are other areas involved in processing of visual information. For example, these blind people should be expected to have a normal day/night cycle, since their melanopsin receptors in their eyes should still signal their suprachiasmatic nuclei in their brains.
If you "knocked out" (cover, damage, remove, etc) their eyes, these people would not be able to do these things, so the guidance is visual, even if the part of the brain normally responsible for the processing of the sensory information is no longer able to function. Nonetheless, other areas of the brain are able to process that visual information to some degree.
There are different kinds of "blind." I can't remember what point you were trying to make, but I wanted to clarify a little.
Yes, truly astonishing mic curves.
Of course, it is "nothing but" a very well-conceived active noise reduction system. Like a lot of tactical fixes in audio, it works best where the situation is worse and is ideal for a highly reverberant room. In terms of dollars or effort or even real-estate, covering the rear wall with a foot of absorbent would be easier.
But back to flat, I bet that test room with those flat curves (and no "room gain") would sound pretty shy of bass, even ignoring equal-loudness-contour issues. I seem to recall that in an anechoic chamber, there's a sense that the bass is missing (been 40 yrs since I last listened).
Of course, it is "nothing but" a very well-conceived active noise reduction system. Like a lot of tactical fixes in audio, it works best where the situation is worse and is ideal for a highly reverberant room. In terms of dollars or effort or even real-estate, covering the rear wall with a foot of absorbent would be easier.
But back to flat, I bet that test room with those flat curves (and no "room gain") would sound pretty shy of bass, even ignoring equal-loudness-contour issues. I seem to recall that in an anechoic chamber, there's a sense that the bass is missing (been 40 yrs since I last listened).
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The human ear is (or how we perceive sound) is not linear, it's more exponential but has dips in it too.
So really good sound is how you like it accurate sound is something different. Everyone's different so one person may hear something different to some else and say it's not accurate but it would be to how the individual has equalised the system. At the end of the day every system (including the room) is also different so errors could occur although this is not likely in well made systems, it is a possibility.
Boscoe
A foot of fiberglass wouldn't be enough to really damp frequencies below 100Hz. This looks like a good solution for a dedicated theater: mono sub bass, rectangular room, impact on decor, etc.
The author comments that room gain is negated and level has to be increased. Plus, the second wall of subs don't add level. Still, if you EQ to the right bass rise it shouldn't sound bass shy, just no longer resonant.
David S.
It is always a pleasure to discuss with some nice people, such as David S.
While the curves are impressive, is sure looks like the guy lives in a warehouse. Some active noise control is highly tailored to the sound (powerhouse dynamos) or use mic pick-up (Bose earphones), not the room as done here. As soon as you depart from rectangular walls, changes in sound speed, speaker differences, and so on, your effectiveness diminishes. That is not the case with a seriously albeit passively dead end.
I said "absorbent" (not fiberglass)* and a foot isn't bad when you have a few bounces. Also, doing a whole wall wall-to-wall might well catch more bounces than a "theoretically perfect" anti-speaker location.
OK, back to "flat" discussion....
*Great stuff that I use in my motorcycle mufflers - white ceramic foam made for furnace noise, very heavy. I wonder how it would work?
While the curves are impressive, is sure looks like the guy lives in a warehouse. Some active noise control is highly tailored to the sound (powerhouse dynamos) or use mic pick-up (Bose earphones), not the room as done here. As soon as you depart from rectangular walls, changes in sound speed, speaker differences, and so on, your effectiveness diminishes. That is not the case with a seriously albeit passively dead end.
I said "absorbent" (not fiberglass)* and a foot isn't bad when you have a few bounces. Also, doing a whole wall wall-to-wall might well catch more bounces than a "theoretically perfect" anti-speaker location.
OK, back to "flat" discussion....
*Great stuff that I use in my motorcycle mufflers - white ceramic foam made for furnace noise, very heavy. I wonder how it would work?
Hello Dan
I have an HT set-up with good old fashion 1/3 octave Urei 839 analog EQ's on L/R and C and the option to run with Audyssey from my HT Pre Pro an Integra 9.8. I had the Urei's long before the Audyssey. The amount of EQ I use is minimal as it's a last resort. The Audyssey works on top of the existing EQ so the system is very flat to begin with.
You have to watch how Audyssey in implemented for the following reasons. It imposes a HF roll off that can only be defeated in some modes. It also takes a bite out of the 2k region which you cannot take out. What you want is to have the PRO Version that you need to purchase a Key to unlock the added features but you need an installer to come and do. Then you can save a "Flat" curve for music.
For movies I use it sometimes it depends on what sounds better. As far as set-up it takes up to 8 measurements in the room and averages these to get the "house curve". The biggest advantage I can see using it would be the low-end where the room modes dominate. The problem I have with it is the fixed roll-off. It just doesn't work for me in my room. Others may feel different.
Rob
Thanks Rob! That helps me make decisions.
Dave, you know as soon as you say a foot of fiberglass won't absorb down to 100Hz, someone has got to show you up. The grey line here has no absorption, the blue line has a foot of fiberglass--80 inches by 50 inches. Ethan Winer(professional in the field who posts on many forums--esp recording forums Rigid fiberglass density tests) says that more area works better than more depth. I'd agree with him based on everything I've done so far. I'd bet you are right when it comes to a more normal sized panel, but I'm getting significant absorption down to 70 Hz and even a little below 60.
Dan
Dave, you know as soon as you say a foot of fiberglass won't absorb down to 100Hz, someone has got to show you up.
The grey line here has no absorption, the blue line has a foot of fiberglass--80 inches by 50 inches. Ethan Winer(professional in the field who posts on many forums--esp recording forums Rigid fiberglass density tests) says that more area works better than more depth. I'd agree with him based on everything I've done so far. I'd bet you are right when it comes to a more normal sized panel, but I'm getting significant absorption down to 70 Hz and even a little below 60.
Dan
You probably mean "shifting your head sideways away" instead of "Rotating ...". I can very well rotate my head +/-45° AT the listening position without loosing the stereo stage.
Rudolf
That is odd. Mathematically speaking, you are on shaky sand and frankly, I don't think either kind of head movement (depending on amount of movement, of course) leaves the phantom image stimulus intact enough to provide accurate localization.
However, you are right in two senses:
1. the music is still coming from someplace around the speakers or at least that end of the room.
2. you still can imagine the violins are kind of to the left and the cellos kind of to the right. But if some trickster in the recording studio briefly panned the cellos to the left, I wonder if you could really tell, except crudely. You'd very likely still "hear" them to the right because that is where you kind of feel they ought to be. Engineers are esp. susceptible to fooling themselves because they don't believe in phenomena like that.
An easy "parlour trick" and illustration of the power of "imagination" is to fool guests about what speaker is playing - for example when the tiny speakers are playing and people think the big ones are. Or when you brain seems to localize ALL the music seems to be coming from your plasma tweeter.
Footnote: I thank Toole for helping me realize that stereo localization (ping-pong accuracy) is not the sine qua non of music reproduction but only one nice feature. However, testing localization accuracy is a useful research tool.
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Regarding the first point. The math (vectors) were nicely described by Ben Bauer in a couple of JASA papers in the mid '60s IIRC. The issue is angle and not side-to-side movement. The analysis was later extended by others a few decades later.
Regarding the second point. "Imgination" is very powerful. In a more general form this also encompasses the "ventroloquism effect" and its variants. One that we all cheerfully live with everyday
I think the effect Rudolf speaks of depends on proximity. At 3 meters, it's the same for me. At 2, a different story, and at 1, even slight movements are audible. My bet is that room reflections/speaker directivity play a large role in these observations. IOW the level of direct to reflected sound. I brought this up in the sister thread over on PE's TT. Another interesting phenomenon is when I do this in a swivel chair. If I swivel the chair, big difference. Turn my head and nothing readily audible. Now my swivel chair does have a very high back on it so a suspect this plays a big role in this phenomenon as it should actually change the response, but I was thinking it may be the body and shoulders actually turning or the actual distance/speed I'm turning. I've got a swivel stool to try yet. I'll see for myself soon enough.
Dan
Dan
Okay guys, I'll back off on the damping comment.
It is fascinating to see a woofer in-room curve that is flatter than we would believe possible. And unlike with EQ, it would retain that curve over a large area. Note that the special pattern of placement of woofers on the first wall is an essential part of this. Their placement gets rid of the first couple of lateral and vertical modes (as viewed when facing that wall). The Toole book goes into this with a number of sub placements that inherently can't feed particular room modes. Yes, it requires a regular rectangular room and multiple subs in awkward places, but the results may be worth it.
RobH, regarding DSP and the Audesey system. I evaluated the Audesey for NAD while at PSB. It suffers from the same issue that all of the DSP room EQ systems have to face: how to measure the speaker in a way that correlates with how we hear. Since it uses a steady state response they found better results with using a downsloping room curve. As I've mentioned before, that will give you a better chance of the direct sound being flat, but it isn't foolproof. I sat through a couple of sessions with the Audesey guys doing an "automatic" EQ, then tweaking the target curve a little and trying again. They also claim that it reduces seat-to-seat variation which, of course, it can't. EQ for one spot is EQ for all, so seat-to-seat variation can't be reduced or altered in any way.
David S.
There is no need to fall back on special psychoacoustic phenomena.
With a sideway head movement you leave the stereo symmetry which is a precondition for having a working virtual stage. Starting at a certain head distance sideways from the stereo axis the stereo stage will collapse and the virtual voices or instruments will "fall into" the respective loudspeakers.
When you turn your head on the stereo axis you don't violate the stereo symmetry. What happens is the same as when you turn your head away from a real sound source: localisation and source width become increasingly diffuse. But this happens on the stereo stage and there is absolutely no need for this stage to collapse into the loudspeakers. This is what I experience in my setup and which is completely in line with the math involved.
It is only this difference in the "loss of stage" where I am arguing about - not the grade of precision on that stage.
Rudolf
Hi,
Obviously everything in perception falls back to psychoacoustics
Without psychoacoustics stereo is nothing more than a interference field of two wavefronts (if neglecting reflections). If considering low frequencues only (and omitting the head), this interference field does not represent a 'natural' wavefront, since the magnitude of the velocity vector is less than unity, that is, the summing wavefront travels with the speed less than speed of sound.
It means in a stereo wave front (at low freqs) the ITD does not behave as it would behave in a natural wave front when turning your head. That is the ITD changes more in a stereo field than in a natural field for the same amount of head turn.
Of course when you insert the head in place it's very complex issue.
Also in practise there is the phenomenon time-intensity trading (see e.g. Blauert) that has implications in lateral movements.
And I still emphasise the high frequency pinna effects that is the most unmerciful knock on the head when robustness of stereo is considered.
P.S. Should 'flat' be considered before or after the interference field?
- Elias
Obviously everything in perception falls back to psychoacoustics
Without psychoacoustics stereo is nothing more than a interference field of two wavefronts (if neglecting reflections). If considering low frequencues only (and omitting the head), this interference field does not represent a 'natural' wavefront, since the magnitude of the velocity vector is less than unity, that is, the summing wavefront travels with the speed less than speed of sound.
It means in a stereo wave front (at low freqs) the ITD does not behave as it would behave in a natural wave front when turning your head. That is the ITD changes more in a stereo field than in a natural field for the same amount of head turn.
Of course when you insert the head in place it's very complex issue.
Also in practise there is the phenomenon time-intensity trading (see e.g. Blauert) that has implications in lateral movements.
And I still emphasise the high frequency pinna effects that is the most unmerciful knock on the head when robustness of stereo is considered.
P.S. Should 'flat' be considered before or after the interference field?
- Elias
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Sure. I was simply writing that we don`t need "special phenomena" in addition to basic psychoacoustics.Obviously everything in perception falls back to psychoacoustics
For having the phantom source 30° off the stereo axis we need approx. ITD=1,5 ms. In natural hearing ITD would be around 0,3 ms for 30°.
1,5 ms corresponds to ca. 50 cm distance at the speed of sound. The delta t (in relation to the loudspeaker distance) I am provoking at each ear by turning my head 90° is about a tenth of that. From that I learn that ITD changes LESS in a stereo field than in a natural field for the same amount of head turn.
Do you have any experience how much of this delta t is needed to destroy the illusion of phanton sources?
I was explicitly NOT talking about lateral movement, but about rotating the head.
This is just a statement. Why shouldn`t the pinna effects work for the stereo source in the same way as for natural sources?
Rudolf
BTW: Have you tried for yourself what happens to the sound stage between your loudspeakers, if you turn your head? Isn't it different from moving your head sideways?
Pray tell us, Rudolf, just what do you mean?
Do you mean that some phenomena (like the speed of sound) are real but some (like the ability to localize sound or the Ventriloquist Effect) are not?
Stereo ITD cannot possibly change less with head rotation because in the stereo interference field the phase isobars are physically more dense than in a natural sound field. Thus when the two ears are harvesting the signal in space from their locations the signals inputting to the ear canals are having bigger phase difference in a stereo field than in a natural field for a given head rotation.
To experience a valid test on ITD one should limit the signal below about 700Hz when using speakers, or use earplugs to avoid other mechanisms to dominate over ITD.
The pinna spectral notches are different for a sound source directly in front and for 30 degrees side. Thus the phantom image (in front) will not generate natural pinna spectral notches as a real sound source placed in front would generate.
Usually when I turn my head (even slightly) I hear two tweeters at the speaker locations. This seems to be individual.
- Elias
To experience a valid test on ITD one should limit the signal below about 700Hz when using speakers, or use earplugs to avoid other mechanisms to dominate over ITD.
The pinna spectral notches are different for a sound source directly in front and for 30 degrees side. Thus the phantom image (in front) will not generate natural pinna spectral notches as a real sound source placed in front would generate.
Usually when I turn my head (even slightly) I hear two tweeters at the speaker locations. This seems to be individual.
- Elias
Bentoronto,
I can`t see where I denied the reality of certain effects.
In forums I try to mainly discuss things which can be experienced and shared by others. That would be my definition of reality for this discussion. If I would be the only one to experience something and all others fail to, this something would perhaps be un-real. Sort of a daydream.
Under this definition the Ventriloquist effect for instance is reality for sure.
Where I possibly fail is my ability to sort the different effects into the different levels of non-, sub-, or whatever else consciousness. I plainly believe that what I was describing is happening at a lower/older level of brainwork than Ventriloquism. But obviously you are the expert to correct me in that regard.
Rudolf
I can`t see where I denied the reality of certain effects.
In forums I try to mainly discuss things which can be experienced and shared by others. That would be my definition of reality for this discussion. If I would be the only one to experience something and all others fail to, this something would perhaps be un-real. Sort of a daydream.
Under this definition the Ventriloquist effect for instance is reality for sure.
Where I possibly fail is my ability to sort the different effects into the different levels of non-, sub-, or whatever else consciousness. I plainly believe that what I was describing is happening at a lower/older level of brainwork than Ventriloquism. But obviously you are the expert to correct me in that regard.
Rudolf
A gracious response. Thanks.
I'd say the hierarchy of what needs to be taken into account in any analysis should be based on what has the biggest effect. If the Ventriloquist Effect swamps all other factors such as loudness, timing-precedence, echos... (as it usually does!), then that kind of "soft" factor needs to be addressed first. Which is why careful experimenters like Toole will always have the speakers behind curtains - in his case, it is to enable his testing to be free of the Ventriloquist Effect so that he can explore other factors.
What concerns me, esp. in this forum of real and wanna-be engineers (myself included) is an implicit hierarchy based on which factors are most easily handled geometrically or numerically, with "soft" factors downgraded to "special" status. That is wrong.
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