ears vs. microphones - a question about spatial localization

Discussion in 'rec.audio.pro' started by jnorman, Aug 30, 2003.

  1. jnorman

    jnorman Guest

    ears are not like microphones. mics can present the difference
    between left and right due to time/intensity differences. ears,
    however, can also differentiate between high and low, which mics
    cannot do. since i can only picture the ear working due to how much
    the cilia are disturbed, can any of you tell me how the ear can tell
    whether a sound source is above or below your head?
  2. Carey Carlan

    Carey Carlan Guest

    jnorman34@comcast.net (jnorman) wrote in
    news:e340b423.0308301026.14a86091@posting.google.com:

    > ears are not like microphones. mics can present the difference
    > between left and right due to time/intensity differences. ears,
    > however, can also differentiate between high and low, which mics
    > cannot do. since i can only picture the ear working due to how much
    > the cilia are disturbed, can any of you tell me how the ear can tell
    > whether a sound source is above or below your head?


    By the shape of your ear.

    Microphones are symmetrical on several axes. Ears are not. The brain can
    interpret the effect of the ear on the sound to sense some spatial
    presence.

    The average person does not percieve up and down very well except in
    extreme cases.
  3. Bob Cain

    Bob Cain Guest

    jnorman wrote:
    >
    > ears are not like microphones. mics can present the difference
    > between left and right due to time/intensity differences. ears,
    > however, can also differentiate between high and low, which mics
    > cannot do. since i can only picture the ear working due to how much
    > the cilia are disturbed, can any of you tell me how the ear can tell
    > whether a sound source is above or below your head?


    The shape of the pinnae and their placement on the head
    introduces small and complex differences in the magnitudes,
    phases and times of arrival of sounds that arrive at each
    ear depending on the location in space of their source. The
    brain, being a massively parallel and extremely complex
    processor is very good at teasing simple meaning out of
    those complex differences.

    IOW, we really don't know how the hell it does it. :)


    Bob
    --

    "Things should be described as simply as possible, but no
    simpler."

    A. Einstein
  4. The New Stereo Soundbook discusses this in some detail. There are
    subtle time differences, and some frequency shifts, the latter of
    which can be duplicated that are involved. It is a complicated matter,
    and has to do not only with the shape of the ear, but how sound is
    traveling around the head and body.


    On 30 Aug 2003 11:26:05 -0700, jnorman34@comcast.net (jnorman) wrote:

    >ears are not like microphones. mics can present the difference
    >between left and right due to time/intensity differences. ears,
    >however, can also differentiate between high and low, which mics
    >cannot do. since i can only picture the ear working due to how much
    >the cilia are disturbed, can any of you tell me how the ear can tell
    >whether a sound source is above or below your head?


    Willie K. Yee, M.D. http://www.bestweb.net/~wkyee
    Developer of Problem Knowledge Couplers for Psychiatry http://www.pkc.com
    Webmaster and Guitarist for the Big Blue Big Band http://www.bigbluebigband.org
  5. Bob Ross

    Bob Ross Guest

    jnorman wrote:

    > ears are not like microphones. mics can present the difference
    > between left and right due to time/intensity differences. ears,
    > however, can also differentiate between high and low, which mics
    > cannot do. since i can only picture the ear working due to how much
    > the cilia are disturbed, can any of you tell me how the ear can tell
    > whether a sound source is above or below your head?


    The fancy term is "Head Related Transfer Function" -- it refers to the
    spectral filtering that the size/shape of the skull & size/shape of the
    outer ear perform that provide localization cues which can't otherwise
    be easily described by Interaural Time Differences or Interaural
    Amplitude Differences.

    But it really comes down to the way the human brain *interprets* that
    filtering, which is why mics aren't very good at discriminating that
    information: In theory some HRT can be approximated with baffles
    (Jecklin or Schneider) or dummy heads (Binaural etc), but without a
    cognitive machine to sort out that info it gets very difficult to convey
    the Z axis with a stereo pair of mics.

    /Bob Ross
  6. philicorda

    philicorda Guest

    "jnorman" <jnorman34@comcast.net> wrote in message
    news:e340b423.0308301026.14a86091@posting.google.com...
    > ears are not like microphones. mics can present the difference
    > between left and right due to time/intensity differences. ears,
    > however, can also differentiate between high and low, which mics
    > cannot do. since i can only picture the ear working due to how much
    > the cilia are disturbed, can any of you tell me how the ear can tell
    > whether a sound source is above or below your head?


    The resonances of the outer ear provide 'below and above' spatial
    information. The shape of the outer ear is not accidental. :) Visual cues
    are very important too, If you can't see whether a sound source is above
    you, its harder to hear it as 'above'.
  7. jnorman wrote:

    >... tell me how the ear can tell
    > whether a sound source is above or below your head?


    and several folks responded about asymetries and
    directional response differences of the ear,
    but when it comes down to it, you've got to cock
    your head to figure out where the sound's coming from.

    -- Gid
  8. David Satz

    David Satz Guest

    Beware of asking the wrong question and getting the right answer. The
    discussion of ears vs. microphones here is well informed, but irrelevant.

    jnorman wrote:

    > ears are not like microphones [ ... ]


    .... but that's OK since we don't plug the outputs of the microphones
    directly into our nervous system in place of the signals from our ears.
    Instead we reproduce two channels of sound over loudspeakers in a room,
    or through headphones. From there, the sound (altered by the processes
    of its transmission and reproduction) goes through everything that the
    ears and brain know how to do for us.

    It's not any limitation of microphones as such that keeps us from hearing
    height information in a conventional stereo playback. You could take any
    conventional stereo microphone arrangement, rotate it 90 degrees--aiming
    one microphone "center up" and the other "center down"--and play the
    recording back through similarly placed loudspeakers; you'd reproduce the
    height information just fine. But then would you ask what "limitation" of
    microphones keeps them from picking up side-to-side information?

    I don't think so. By then it would be completely obvious that it's our
    usual method of two-channel pickup and reproduction that imposes the
    limitation. It is designed to reproduce only lateral information, plus
    some degree of implied depth, while excluding height information.

    To get all three dimensions we need at least three channels of pickup and
    transmission (with at least one channel above or below the other two)--then
    suddenly and miraculously, microphones would "know" how to convey all the
    necessary information to reproduce height cues.
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    On 2003-08-31 mr_furious@mail.com(BusterMudd) said:
    >>when it comes down to it, you've got to cock your head to figure

    >out where the sound's coming from. >
    >Call me a freak then, but I have no problem determining a sound
    >source's location anywhere within a three dimensional sphere without
    >changing the orientation of my head.

    Ditto here, but it's a skill I probably had to develop.

    People are always asking this old blind man if my ears aren't better
    than therir ears. I always explain it in the context of a guy who
    propels himself with his arms in a wheelchair. NOte the better upper
    body muscle development. same goes for this skill. mOst folks look
    for correlation between ears and eyes ot localize a sound source. IN
    fact, I'd say my ears are not quite as good as some folks' these days,
    too many loud bandstands in my younger days without ear protection.


    REgards,



    Richard Webb
    Electric Spider Productions
    No email, use this group and a subject of
    "ping RIchard WEbb" I'll email you.


    --
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    On 2003-08-31 936ad1fd.0308310857.6b672539@posting.google.com said:
    >When birds want you (or some other bird) to know where they are
    >they sing a nice melody with sustained pure tones, but when
    >they don't want you (the approaching predator) to know where
    >they are, the squawk very short multi-frequency bursts. Try
    >locating those warning calls with your head in a rigid clamp.
    >I'm not saying that you can't perceive direction without head
    >movement; I'm saying you're handicapping your localization
    >ability by not moving. You can do left-right localization
    >with pure intensity cues, and you can do it with just phase
    >cues, but neither alone are realistic.

    True. I weighed in on this thread and I guess over generalized as
    well. IT's often easier to localize sound even for this old blind man
    if I'm facing it directly. Good point about the bird calls and the
    differences.

    HOwever, for most sounds we encounter it's fairly easy to get spatial
    clues without moving your head. Try it sometime. get one of those
    sleep shades from the drustore and put it on then go to a busy place.
    HEr's an experiment for you. stand at a busy intersection. LIsten to
    the traffic movement. wHen traffic moving parallel to your direction
    moves the light is green, you can assume that it is green for you and
    you can safely cross the street.

    YOu can localize the traffic sounds easily. NOw try the sound of a
    jackhammer in the concrete canyons of the inner city. This one's
    going to bounce around a bit until you're right on top of it making it
    harder to judge where it is. Ever hear that police or emergency
    vehicle siren while driving and not be able to ascertain from hwere it
    is coming and which way it's going? My wife always asks me as I seem
    to have an easier time localizing it.


    >I think we overlook the motor component of binaural hearing
    >partly because it's so unconscious and partly because it
    >makes the already intractible math that much more complicated.

    Quite possibly so, but remember that our ears are shaped and aimed so
    as to give us the most benefit from their directionality when we face
    the sound source. Nice example about the blindfolded kittens versus
    those completely swaddled.

    Regards,




    Richard Webb
    Electric Spider Productions
    REplace anything before the @ symbol with elspider for real email

    --
  11. Buster Mudd

    Buster Mudd Guest

    Gidney and Cloyd <gidney_n_cloyd@yahoo.com> wrote in message news:<xbd4b.17277$Ih1.6301171@newssrv26.news.prodigy.com>...


    > but when it comes down to it, you've got to cock
    > your head to figure out where the sound's coming from.
    >



    Call me a freak then, but I have no problem determining a sound
    source's location anywhere within a three dimensional sphere without
    changing the orientation of my head.
  12. > We, Gidney and Cloyd, wrote:
    >
    >> but when it comes down to it, you've got to cock
    >> your head to figure out where the sound's coming from.


    Buster Mudd wrote:

    > Call me a freak then, but I have no problem determining a sound
    > source's location anywhere within a three dimensional sphere without
    > changing the orientation of my head.


    Really? For all directions and for all sound sources?

    When birds want you (or some other bird) to know where they are
    they sing a nice melody with sustained pure tones, but when
    they don't want you (the approaching predator) to know where
    they are, the squawk very short multi-frequency bursts. Try
    locating those warning calls with your head in a rigid clamp.

    I'm not saying that you can't perceive direction without head
    movement; I'm saying you're handicapping your localization
    ability by not moving. You can do left-right localization
    with pure intensity cues, and you can do it with just phase
    cues, but neither alone are realistic.

    I think we overlook the motor component of binaural hearing
    partly because it's so unconscious and partly because it
    makes the already intractible math that much more complicated.

    I speculate that there would be an auditory analogue to that
    fameous cognative development experiment where blindfolded
    kittens learned to see, but swaddled kittens were blind for life.
    If you can't move around and interact with the soundfield,
    your brain will never learn build a 3-D model of the world.

    -- Gid
  13. Scott Dorsey

    Scott Dorsey Guest

    jnorman <jnorman34@comcast.net> wrote:
    >ears are not like microphones. mics can present the difference
    >between left and right due to time/intensity differences. ears,
    >however, can also differentiate between high and low, which mics
    >cannot do. since i can only picture the ear working due to how much
    >the cilia are disturbed, can any of you tell me how the ear can tell
    >whether a sound source is above or below your head?


    It's due to the earlobe itself, which results in the ear having a varying
    frequency response off-axis. The brain learns to localize sounds based on
    that. Tape your earlobe down with gaffer tape and you will totally lose
    both height localization and front-to-back localization. It is eerie.
    --scott
    --
    "C'est un Nagra. C'est suisse, et tres, tres precis."

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