OT: Can you tell the difference between sounds behind you and in front of you?

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According to this:
http://www.school-for-champions.com/senses/hearing_direction.htm#.VuHuWZKzB48
"some people can tell if the sound is in front or behind them."
I've never heard of that before. Can you?
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On 3/10/2016 3:03 PM, Mr Macaw wrote:

Depends on the shape of the pinnae and the quality of your "auditory meatware".
Azimuth (left/right) is relatively easy for most folks. Elevation gets a bit harder for many. Front/rear is the hardest (esp if you want to express WHERE to the rear, etc.).
Your brain tends to rely on time differences, amplitude differences and frequency attenuations to discriminate direction.
A sound coming from the left is louder at the left ear than the right (because the right ear is in your "head's shadow"). It is also slightly earlier than its arrival at the right ear (a foot is about a millisecond delay). Additionally, higher frequencies are attenuated more than low due to the "meat" in the middle. And, finally, environmental characteristics (room acoustics, etc.) come into play (your brain adds context to better qualify the data that your ears are providing.
For a hoot, visit an elliptical room (my favorite exhibit at the Museum of Science & Industry, Chicago) and stand on a focus (ellipse can be considered a circle with two "centers") while a friend stands on the other. Your BRAIN knows your friend to be ~20 feet away. And, you are SURROUNDED by noisey tourists walking in every direction -- including directly behind you!
Yet, when your friend *whispers*, you will swear their lips are inches from your ears!
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Now that I don't believe. I'm sure it's all volume. The time difference would be far too small to be of use. The volume is much more obvious.

There was a film once where a blind man could tell exactly where everything was in a room by echo location when he made a noise.

I've heard of those, but never tried one.
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On 3/10/2016 3:21 PM, Mr Macaw wrote:

You'd be wrong. ITD (Interaural Time Differences -- differences between left and right ears in the time domain) are used for low frequencies (e.g., below about 1KHz). Low frequencies are not attenuated much (which is why you can hear the bass notes from the guy's sound system in the car next to you through closed windows -- but can't hear any of the vocals!)
ILD (Interaural Level Differences) are used for higher frequencies -- where the signal experiences *more* natural attenuation.
*You* can perceive time differences on the order of 10 MICROseconds.
You can probably resolve azimuth (left-right) to within *1* degree if the sound is sort-of in front of you. Once it starts to move off to the sides, your "resolvability" gets much worse (10-15 degrees).
The most interesting aspect of this is that you can recreate these "situations" on a computer -- with headphones -- and the listener will hear the sound as originating *inside* his/her head!
[I've written a "3D spatializer" that allows me to present sounds to a (blind) user in much the same way that your eyes would perceive "notifications" in the visual field. Ideally, it has to be tailored to each individual user as each user's "audio meatware" is different.]
Notice how often you MOVE (tilt) your head when trying to identify the location/source of a sound! Or, "focus" on it.
Ever notice how you can hear someone mentioning your name in a crowded room -- despite being unable to hear anything else they are saying??
Hearing (like vision and the other senses) is delightfully complex!
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If you aim one ear towards a bass note and the other away from it (i.e. the note is on your left), your left ear will hear it louder, that is a fact. Not because it's closer, but because the sound doesn't have to go round corners to get to that ear. You simply don't need any other method.
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On 3/13/2016 1:14 PM, Mr Macaw wrote:

Since I wear hearing aids, I often can hear sounds that I don't recognize, and I can't tell which direction it's coming from regardless of how I turn my head.
--
Maggie

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On 3/13/2016 3:40 PM, Muggles wrote:

That's the sound generator Don and Philo put in last year. It's designed to drive you crazy. Danny D found the plans on the net, and I picked the lock on your door for us to get in.
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http://mynoise.net/NoiseMachines/desertedSoundscapeGenerator.php
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small to be of use. The volume is much more obvious.
OK, don't believe it. It's true just the same. The human brain is *very* sensitive at distinguishing the timing of sounds. We're much better able to tell which of two nearly simultaneous sounds occurred first than we are which of two nearly simultaneous sights.
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difference would be far too

sensitive at

of two nearly

simultaneous sights.
Agree. The human brain is exquisitely capable of detecting slight phase shifts. Even tiny bat brains can do it quite well. http://www.thenakedscientists.com/forum/index.php?topic (653.0
says:
<<David Corey compares the arrangement to the strings of a grand piano, with the high notes at the base of the cochlea, where the basilar membrane is narrow and stiff, and the bass notes at the apex, where the membrane is wider and more flexible. Hair cells also convey basic nformation about the intensity and duration of sounds. The louder a sound is at any particular frequency, the more vigorously hair cells tuned to that frequency respond, while their signaling pattern provides information about the timing and rhythm of a sound. Konishi hypothesized that such timing and intensity information was vital for sound localization. So he placed microphones in the ears of owls to measure precisely what they were hearing as the portable loudspeaker rotated around their head. He then recorded the differences in time and intensity as sounds reached each of the owl's ears. The differences are very slight. A sound that originates at the extreme left of the animal will arrive at the left ear about 200 microseconds (millionths of a second) before it reaches the right ear. (In humans, whose sound localization abilities are keen but not on a par with those of owls, the difference between a similar sound's time of arrival in each ear would be about three times greater.)>>
It takes a rather simple neural comparator "circuit" in the brain to detect which sound arrived first. That type of ability is found in pretty primitive animals. But clearly intensity and timing are both integral parts of 3D auditory location techniques. IIRC, bats, owls and certain prawns easily can detect phase shifts and use the doppler effect to determine the speed of their prey.
It's remarkable that such complex structures arose within animals. The different neural net sensors in our bodies is much like photocells, microphones, thermocouples, piezo-electric pressure sensors and more evolving on their own. Your hair follicles are sensitive enough to know which way your hairs are aligned and to erect them on neural command.
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Bobby G.



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Hi Bobby,
On 3/11/2016 2:44 AM, Robert Green wrote:

Play two sine waves at equal amplitudes and fudge the phase of one relative to the other.
Note that you "consciously" perceive sounds arriving within several milliseconds of each other as "one" sound. (I think around 50ms is where you start to become conscious of "echoes", etc.). Yet, your brain is processing times 1000 times shorter than that as it attempts to "localize" those sounds!

"Three times greater" cuz we have fatter heads! :> Three times longer distances involved!

Some creatures rely on more "mechanical" means (e.g., directly coupling the eardrums so the "difference" is available as a directly observable signal).

So much for the "intelligent design" theory! I.e., if you can create EVERYTHING (including "radiation"), then why create a system that requires so many different solutions to the same problem? Why don't *our* ears move like those of dogs? Why aren't our eardrums directly coupled like flies? Why don't all of our pinnae look the same? etc.
OTOH, if you are ADAPTING to an environment IMPOSED on you, you EVOLVE solutions that address those particular needs in the context of your own orgainsm, etc.
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<stuff snipped>

I think you're missing the bigger picture. Why would life forms even "want" to solve problems in the first place? What propels different species of animals to keep changing their design, so to speak? It happens at the cellular level as well. Mitosis is a religously inspiring experience because *something's" making all those strands of DNA and RNA dance in a way that makes them replicate.

Convergent evolution may be proof of an over-arching intelligent force. Why do life-forms evolve separate solutions to the same sorts of problems? Why does life seem to *want* to evolve? What drives life-forms to solve these problems at all? Why do insects with ultra-fast jaws appear to evolve that trait independently with completely different gene sets and completely (AFAWK) on their own on different continents? What force compels birds to become more keen-sighted generation after generation?
What explains the creation of the incredible forms of mimickry that exist? These could be just random mutations, as some suggest, but I believe they're an evidence of the very essence of a "life force" that propels life forward. Is it God? As we said in the Pentagon, that's above my pay grade, sir! But it is food for thought.
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Bobby G.



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The only thing it's evidence of is either your lack of intelligence, or your over active ability to be amazed by things. Don't forget, these evolutions happen over many many many generations. If there was a god involved, it would be far quicker. You don't need 6.5 billion people on earth through 100s of generations to decide you need to change something. And it would also change in everyone, not just randomly.
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On 3/11/2016 2:44 AM, Robert Green wrote:

In addition to time and intensity, there are also differences in how particular frequencies are perceived. I.e., higher frequencies are attenuated more (by the "acoustical shadow" cast by your head) than low frequencies.
The same sort of experiment (outlined above) is performed on people to quantify their HRTF (Head Related Transfer Function -- how different types of sounds are perceived IN EACH EAR CANAL based on where they originate in the three-dimensional space surrounding them).
In: <
https://i2.wp.com/resource.isvr.soton.ac.uk/FDAG/VAP/images/me_anec.gif
you can see microphones inserted in the subject's ear canals (as close to the tympanic membrane as feasible).
The baffles in the anechoic chamber (floor/walls/ceiling) damp out reflections.
The speakers arranged in the arch over the subjects head present the sound source in one of N "relative directions" (the subject's head is located in the "center" of that arc).
The arc pivots so that the speaker array can be behind, above, infront, etc of the subject. So, in effect, you can issue the sound source from any position in a SPHERE surrounding the subject's head.
You can replace the human subject with a KEMAR head <http://kemar.us/ and obtain data for a generic head (vary the size, change the shape/orientation of the pinnae, etc.).
Unfortunately, the data from one subject (or, a KEMAR) isn't directly applicable to other subjects. Normal variation in our anatomies means that the HRTF for *your* head is different from that of any other person.
The takeaway from all this is that, in theory, you can manipulate any sound source, mathematically, and present it to a user via headphones and convince him that the source is at a specific point in space relative to his head. *If* you have HIS particular HRTF encoded in that mathematical algorithm!
Where this falls down is in the dynamics of perception: you will tend to react to a sound stimulus by altering your position, head orientation, etc. relative to your guesstimate as to where the sound is located. I.e., you'll twist your neck, tilt your head, etc. -- waiting for a repeat of that signal to give you a refined estimation of where the source is located.
With the synthesized approach, moving your head MOVES THE SOURCE (because the headphones don't know that your head is now pointed in a different direction -- so, the signal that it presents is STILL "off to the left" just as much as it was before you moved your head!) You can work-around this by using a head-tracking device and dynamically tweeking the math (signal processing) to reflect the head's motions (to adjust the signals to each ear so the sound source stays fixed in space as the head reorients to try to refine its position).
[In my case, I rely on different *sounds* in different *places* so the user doesn't have to know exactly where a sound originates: "Ah, that signal off to my left means someone is at the front door; had it appeared to my right, I would know it was the BACK door!"]
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I doubt it, it's just not needed. There's the far simpler method of just analysing the volume.
Try this: sit in front of your stereo with the speakers in the usual place, equidistant from your head, one on the left and one on the right. Move the balance control around, and the sound appears to come from different places. This works equally well for all frequencies. All the stereo has done is change the volume of each speaker, it doesn't alter phase or timing at all.
Now you might be thinking of surround sound at this point.... "stereos" with many speakers around the room only work because you might move your head a bit. Try a fake surround sound generated by only two speakers using your computer, and it just doesn't work.
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That's amazing: https://youtu.be/TeFRkAYb1uk Which claims he's the only one, but clearly not, https://youtu.be/2IKT2akh0Ng
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Per Mr Macaw:

Depends on the sound.
Most sounds: yes.
But the warning sounds that the local emergency vehicles make are so loud or *something* that I cannot tell where they are coming from.
Whoever buys that stuff probably thinks louder is better - like the morons who set the sound level in theaters... but it seems counter-productive to me.... but maybe it's just me...
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Pete Cresswell

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Hi Pete,
On 3/10/2016 3:46 PM, (PeteCresswell) wrote:

It is a combination of loudness, narrow frequency range and "anxiety". Add to that the "canyon" effect in many roadways (buildings on each side funneling the sound in a corridor).
There has been some research that suggests you need a combination of an "attention getter" (like the current siren) coupled with a wide-band noise source (imagine the sound of a crowd of people) to help folks sort out the direction of the "alarm".

Each intersection, here, has a strobe light situated atop one of the lamp posts/traffic signals *in* the intersection. A strobe light on the emergency vehicle signals the intersection that it is approaching. The traffic controls then automatically adjust/abort the current cycle to favor the direction of the approaching emergency vehicle (the thinking being to get any cars sitting at the light MOVING, out into the intersection and "mobile" so they can avoid the emergency vehicle).
We have accustomed ourselves to watch for the blinking strobe light *in* the intersection (it blinks as an apparent acknowledgement of the strobe on the emergency vehicle) to start looking (and listening) for the vehicle -- expected shortly.
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Per Don Y:

We have the auto-green for approaching emergency vehicles but, AFIK, not the strobe lights.... OTOH, maybe they are there, but I have not seen them.
Last couple emergency vehicles I watched managed to charge into the intersection before the light had even changed for them.... And when it does change, it's just a *flick* and it's red.... no warning for the other traffic.
Sounds made-to-order for revenue producing tickets.
--
Pete Cresswell

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On 3/10/2016 6:19 PM, (PeteCresswell) wrote:

The strobe light tells us (me), "watch to see whether you get a quick red *or* an early green". This then tells me the vehicle is either coming up from behind me/approaching head on (in the case of *me* getting a green) OR coming from the right/left sides (in the case where I get a red).
In essence, it cuts my choices in half so somewhat improves my odds of noticing the vehicle BEFORE it gets to the intersection.

Here, an emergency vehicle can often get tied up BEHIND traffic queued at a light. As we have median strips at most of the larger intersections, it's not easy for a vehicle to cross into the "wrong" lane to navigate around cars "parked" at the light.
Prior to the strobe gizmo, there were numerous cases where I found myself at the head of my lane and took the initiative to CAREFULLY cross the intersection on RED just to make a hole for the vehicles behind me to get out of the way.
[Of course, all the "seniors" sit their stupefied: "Should I go? But the light is red!?" Instead, they wait until the emergency vehicle is on their back bumper leaning on it's "foghorn" to make up their mind that they MUST go...]

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