Cardioids crossed at 90 degrees

Discussion in 'rec.audio.pro' started by James Boyk, Aug 21, 2003.

  1. I'd have to suggest that, in application, it's the application itself that
    specifies whether it works or not. But, again, I'm talking about an
    application whereby my results are from a closely mic'd piano with 90 degree
    cardioids, not a room where an orchestra is playing. In a more ambient
    situation with acoustic instruments I'd be more likely to simply mic a piano
    outside of the shell in mono because other than the piano player, the
    instrument is really only heard in mono, although if it's in a really nice
    hall I'd go for the Blumlein. Again, application specifies the use. I'd be
    more than willing to agree that a 90 degree cardioid setup would not be what
    I'd use for a room recording, no matter where I could put the mics. I
    believe your experience probably represents more along the area of classical
    recordings in decent rooms, judging from your bona fides. On the other
    hand, I'm doing big bands and small jazz combos and sometimes 12 or more of
    them mixed and matched throughout a day. Room recordings aren't a
    consideration, so techniques that you and most would use possibly don't
    really apply. I like having room mics when possible, but they are going to
    be hanging from some lighting rig out of the way of the crowd, and certainly
    conceivably not in the most correct position for such work. I don't get the
    big jobs where I'm in a 3,000 sq ft live room of a studio.

    Didn't you use to have a website listed on your signature James? If you've
    got one, I'd like to visit it. Perhaps you have some of your demo stuff
    available?

    --


    Roger W. Norman
    SirMusic Studio
    Purchase your copy of the Fifth of RAP CD set at www.recaudiopro.net.
    See how far $20 really goes.




    "James Boyk" <boyk@caltech.edu> wrote in message
    news:bi80am$118$1@naig.caltech.edu...
    > Well, I don't know how to answer. You cannot judge the matter by looking

    at two 3-digit numbers and saying Gee, they're not so very different from
    each other. You can judge only by listening. The question was whether
    90-coincident-cardioids image correctly. They don't; they don't come close.
    I suggest that the virtues of the best stereo arrays, and the defects of
    others, will become more vivid to you if you listen to our demo recording.
    It's your privilege not to care about imaging---though personally I think
    it's of fundamental importance to successful recording, for a reason I
    haven't gone into here---but facts are facts; and the fact is that
    90-coincident-cardioids don't work well in theory or in practice.
    >
    > James Boyk
    >
  2. Sugarite

    Sugarite Guest

    > Somone mentioned a new stereo mike that embodies coincident cardioids
    crossed at 90 degrees. I find it odd to use this arrangement, since the
    stereo given by this arrangement is much too narrow, and is also irregular
    in movement across the stage. This has been noted by others in the group in
    other contexts, and is also shown in the stereo miking demo recording made
    in my lab.
    >
    > On the other hand, what should the mike be instead? If it were

    ORTF--arguably the best you can do if you're confined to cardioids--it would
    be physically more awkward, and probably more vulnerable to damage. But
    perhaps 120 degrees would have been usefully better. As long as they were at
    it, though, why not make a coincident, 90-degree pair of
    condenser....figure-8's? Even go all the way and make single-diaphragm
    fig-8's, like the Schoeps MK-8.

    I own a Rode NT4 (which is a coincident cardioid XY small diaphram pair like
    you describe) and use it often for stereo location recordings. Serveral
    issues haven't been addressed in all the other replies in this thread, so I
    figured I'd start from the top:

    Firstly, post processing is always required to tame a location recording to
    be even remotely realistic. The widening of a 90 degree cardioid XY pair is
    just one of many processes that must be done, and even though another mic
    format might be better suited to rendering more natural imaging before post,
    it's a minor issue compared to other factors, one of which is proper
    rejection. I don't claim to know exactly why 90 degree coincident cardioids
    can offer the best imaging, but I'm going to offer a plausible explanation
    for the specific circumstances of a live concert, which can also apply to
    other environments.

    Most PA speakers at music venues are mounted parallel to each other, so the
    mic has to be towards the rear of the room to get decent direct sound from
    the horns especially. The rejection pattern of the cardioid XY is such that
    when the stereo image is widened during post, the resulting rear information
    becomes an amalgomation of what was originally mostly side information, so
    the perceived position of the listener is a lot closer than the mic actually
    was. It's the best of both worlds - the balanced mix, ambience, and
    frequency response of a mid-rear location combined with the scope, impact,
    and potency of the front row.

    Here's an example of this technique:
    http://www.thetrewsmusic.com/media/mp3/060703-tow.zip
    The mic was actually about 50' back from the stage in one of my favorite
    recording venues (Kee to Bala, Muskoka region, Ontario, Canada), and yeah
    it's rather squashed to let the room ambience add some hugeness too it, it's
    a promotional clip on the band's website...

    It is NOT the same as placing the mic closer and using a wider differential
    angle. If the mic were as close as it seems, it would not have had the
    clarity or balance that can only be found within the good dispersion area of
    the PA speakers. A wider differential angle would not allow for as much
    perceived proximity improvement, and a narrower angle wouldn't offer enough
    side info to work with. A pair of omni's would render a big pile of mud by
    comparison, and figure-8's would slew the rear imaging and leave a gap up
    front. AFAIK the cardioid XY pattern is the only way to acheive this
    effectively, probably because the 90 degree angle represents the separation
    between the two independent component vectors of the forces imposed on a
    single positon in two dimensions, hence the term "XY", much like the grooves
    on stereo LP's. I haven't done enough recording of acoustic performances to
    comment concisely, but there are again advantages to a rear mic placement
    with widening during post, and so far that process hasn't failed me.

    I also strongly discourage using separated mics for the differential delay
    imposed. I've heard the argument to death that it makes sense because our
    ears are separated and the human auditory system depends on differential
    delay for imaging, but we're recording for a stereo, not a human auditory
    system. AFAIK nobody makes a CD player that plugs directly into the
    cerebral cortex. A stereo and the listener's ears do their part on their
    own and I see no reason to make special accommodations for this particular
    aspect. Coincident mics pick up the stereo image found at one position,
    then a properly configured stereo allows the listener to assume that
    positon. It is impossible for a listener to be in two positions, and also
    impossible for a stereo to reproduce two postions, so having mics in
    different positions generally makes about as much sense as putting legs on a
    car.
  3. James Boyk

    James Boyk Guest

    Sugarite wrote: Firstly, post processing is always required to tame a location
    recording to be even remotely realistic.


    You must work in an entirely different genre from anything I've experienced. Granted, I do only a very limited kind of thing; but it involves *avoiding* all unnecessary processing and for that matter all unnecessary gain stages, to keep the sound as pure a
    s possible.



    > ...The widening of a 90 degree cardioid XY pair is just one of many processes that must be done,


    You convert XY to MS, increas the proportion of S, then convert back to XY?



    > ...and even though another mic
    > format might be better suited to rendering more natural imaging before post,
    > it's a minor issue compared to other factors, one of which is proper
    > rejection. I don't claim to know exactly why 90 degree coincident cardioids
    > can offer the best imaging, but I'm going to offer a plausible explanation
    > for the specific circumstances of a live concert, which can also apply to
    > other environments.


    Live rock concert, that is.



    > Most PA speakers at music venues are mounted parallel to each other, so the
    > mic has to be towards the rear of the room to get decent direct sound from
    > the horns especially. The rejection pattern of the cardioid XY is such that
    > when the stereo image is widened during post, the resulting rear information
    > becomes an amalgomation of what was originally mostly side information, so
    > the perceived position of the listener is a lot closer than the mic actually
    > was. It's the best of both worlds - the balanced mix, ambience, and
    > frequency response of a mid-rear location combined with the scope, impact,
    > and potency of the front row.


    I'd love to hear "before" and "after" examples.



    > Here's an example of this technique: http://www.thetrewsmusic.com/media/mp3/060703-tow.zip


    Can you put this on a web site instead?



    > The mic was actually about 50' back from the stage in one of my favorite
    > recording venues (Kee to Bala, Muskoka region, Ontario, Canada), and yeah
    > it's rather squashed to let the room ambience add some hugeness too it, it's
    > a promotional clip on the band's website...


    > It is NOT the same as placing the mic closer and using a wider differential
    > angle. If the mic were as close as it seems, it would not have had the
    > clarity or balance that can only be found within the good dispersion area of
    > the PA speakers. A wider differential angle would not allow for as much
    > perceived proximity improvement, and a narrower angle wouldn't offer enough
    > side info to work with. A pair of omni's would render a big pile of mud by
    > comparison, and figure-8's would slew the rear imaging and leave a gap up
    > front.


    I don't get this statement about fig-8's.



    > ...AFAIK the cardioid XY pattern is the only way to acheive this
    > effectively, probably because the 90 degree angle represents the separation
    > between the two independent component vectors of the forces imposed on a
    > single positon in two dimensions, hence the term "XY", much like the grooves
    > on stereo LP's....



    I can't follow this.



    > I also strongly discourage using separated mics for the differential delay
    > imposed. I've heard the argument to death that it makes sense because our
    > ears are separated and the human auditory system depends on differential
    > delay for imaging, but we're recording for a stereo, not a human auditory
    > system.



    Huh? A "stereo" listens to your recordings? No, a human listens. We certainly are ALWAYS recording for a human auditory system. And Blumlein showed why the right way to do that is to use coincident fig-8's (or spaced omnis with the "Blumlein shuffler," whi
    ch no one seems to use).



    > ...AFAIK nobody makes a CD player that plugs directly into the
    > cerebral cortex. A stereo and the listener's ears do their part on their
    > own and I see no reason to make special accommodations for this particular
    > aspect. Coincident mics pick up the stereo image found at one position,
    > then a properly configured stereo allows the listener to assume that
    > positon. It is impossible for a listener to be in two positions, and also
    > impossible for a stereo to reproduce two postions, so having mics in
    > different positions generally makes about as much sense as putting legs on a
    > car.


    Well, forgive me, but this is a psychoacoustically naive point of view. Can't it be enough just to say, "Coincident works for me"? There's no need to argue deep perceptual issues.


    James Boyk
  4. Bob Cain

    Bob Cain Guest

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    William Sommerwerck wrote:
    >
    > > I think this is beside the point in any event. For any kind
    > > of real listening environment we don't yet know how to
    > > record something and reproduce it "correctly" in space
    > > as all the discussion on the surrsound mailing list will
    > > clearly attest. I don't think it is possible, frankly, and
    > > think most of the stuff going on is smoke and mirrors
    > > with a lot of persuasive heuristics used to try and justify
    > > the "correctness" of each proposed method.

    >
    > No offense, but you've obviously never heard Ambisonic recordings. I've actually
    > made them, and the sound is much closer to what you hear live than any other
    > speaker-based surround system.


    None taken, but I have. I very much like the illusion that
    is created but I understand the fundamental theory well
    enough to know exactly what can and can't be accomplished
    with a first order recording. Even in an anechoic situation
    with very sophisticated reconstruction methods the best that
    can be accomplished is to recreate at one point in space the
    acoustic field that was measured by the mic. In theory, at
    that one point, the exact time varying sound velocity vector
    and pressure scalar that existed where the recording was
    taken can be recreated but at no surrounding point can
    anything be stated relative to the original sound field in
    which the measurement (recording) was taken.

    In practice, after considering the high frequency
    limitations of the Ambisonic method of measurement, due to
    its lack of true coincidence and the less than ideal nature
    of the microphones, as well as putting that ideal
    reconstruction system in a room with a head at the
    reconstruction point that is attached to a body seated in
    furniture and _all_ bets are off.

    This is not to say that Ambisonics doesn't go a long way to
    creating an illusion that is _very_ satisfying but one can
    simply not say that it is an accurate recreation at the
    listener's ears of the event that was recorded.


    Bob
    --

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

    A. Einstein
  5. Bob Cain

    Bob Cain Guest

    James Boyk wrote:
    >
    > > ...AFAIK the cardioid XY pattern is the only way to acheive this
    > > effectively, probably because the 90 degree angle represents the separation
    > > between the two independent component vectors of the forces imposed on a
    > > single positon in two dimensions, hence the term "XY", much like the grooves
    > > on stereo LP's....

    >
    > I can't follow this.


    It measures the vector velocity component of the acoustic
    field, the pressure gradient, in an orthogonal fashion.
    It's why the Blumlein is at 90 degrees and the same
    reasoning applies to the crossed cardiods which each contain
    the sum of a scalar pressure component and vector pressure
    gradient component.


    Bob
    --

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

    A. Einstein
  6. James Boyk <boyk@caltech.edu> wrote:

    > That was my point. No reason the NT4 couldn't have been fig-8's.



    I don't think the NT4's intended market would understand the advantages
    of a fig-8 over a cardioid. Nor would they understand the advantages
    of 130 degrees over 90 degrees. To the lay person (which includes 95%
    of the recording gear market), it seems counter-intuitive to use
    microphones that pick up sound coming from the opposite direction, or
    to point the microphones someplace other than essentially toward the
    musical source they're trying to record. People who understand the
    geometry of microphone pickup patterns are looking into other brands
    and models of microphone.

    ulysses
  7. James Boyk

    James Boyk Guest

    Bob Cain wrote:
    > It measures the vector velocity component of the acoustic
    > field, the pressure gradient, in an orthogonal fashion.
    > It's why the Blumlein is at 90 degrees and the same
    > reasoning applies to the crossed cardiods which each contain
    > the sum of a scalar pressure component and vector pressure
    > gradient component.


    Sure. But the cardioid embodies the *wrong* sum!

    jb
  8. On Sat, 23 Aug 2003 15:05:27 -0400, "Roger W. Norman"
    <rnorman@starpower.net> wrote:

    > how a single diaphram mic is going to have a charged backplate and
    >have reasonable sound coming in from the back of the 8.


    I've never seen one, but imagine the construction to be
    like a really, really small electrostatic speaker, with
    porous fixed plates and a charged diaphram between.

    A side benefit, if the charge is constant, is an inherent
    linearity missing from conventional single-ended mics.

    Chris Hornbeck
    http://www.votetoimpeach.org/
  9. Arny Krueger

    Arny Krueger Guest

    "James Boyk" <boyk@caltech.edu> wrote in message
    news:bi8chu$502$1@naig.caltech.edu
    > Jerry Steiger wrote: > ...If it's a listening judgment it's an
    > opinion, not a fact.
    >
    > Sorry, I disagree.


    And that's just an opinion, too.
  10. Arny Krueger

    Arny Krueger Guest

    "Roger W. Norman" <rnorman@starpower.net> wrote in message
    news:bi8eru$r88$1@bob.news.rcn.net

    > I'd have to suggest that, in application, it's the application itself
    > that specifies whether it works or not.


    Closer...

    I think we can all agree that is the comparison of actual results to
    *someone's* expectations that determines whether something *works* or not.
  11. > This is not to say that Ambisonics doesn't go a long way to
    > creating an illusion that is _very_ satisfying but one can
    > simply not say that it is an accurate recreation at the
    > listener's ears of the event that was recorded.


    Like many people, you're criticizing Ambisonics for the wrong reasons. I
    interpret this as a perverse excuse for rejecting something that happens to work
    extremely well. And it IS perverse to deny a system that actually takes into
    account how the ears and brain interpret directionality.

    Ambisonic playback comes very close to sounding as if you are actually sitting
    at the mic position. I have never heard any other form of recording and playback
    (except, of course, for binaural) that comes even remotely close. Had Ambisonics
    been widely accepted as a standard recording format, it could have been
    rationally enhanced with HRTF and similar features.

    No one is obliged to use the SoundField mic. My recordings were made with Pearl
    TC-4v mics, and Nimbus has used Schoeps capsules for many years.
  12. On Sat, 23 Aug 2003 10:33:13 -0700, "Jerry Steiger"
    <gwsteiger@comcast.net> wrote:

    > If it's a listening judgment
    >it's an opinion, not a fact.


    "Truth is stranger than fact."
    Grandpa Jones


    Chris Hornbeck
    http://www.votetoimpeach.org/
  13. Bob Cain

    Bob Cain Guest

    William Sommerwerck wrote:
    >
    > > This is not to say that Ambisonics doesn't go a long way to
    > > creating an illusion that is _very_ satisfying but one can
    > > simply not say that it is an accurate recreation at the
    > > listener's ears of the event that was recorded.

    >
    > Like many people, you're criticizing Ambisonics for the wrong reasons. I
    > interpret this as a perverse excuse for rejecting something that happens to work
    > extremely well. And it IS perverse to deny a system that actually takes into
    > account how the ears and brain interpret directionality.


    Then you've interpreted me incorrectly. I loved the sound
    of Ambisonics at the single demo I heard (at that time I
    didn't understand enough about it to even note the speaker
    configuration used for reproduction much less ask about the
    feed transformations) but I don't like the extravagant
    claims made for its "correctness" now that I fully
    understand the theory and practice. I don't think that
    theoretical correctness is necessasary for a system to do a
    damn nice job of capturing something that, when carefully
    reproduced, is very pleasant and plausible. Yes, it does
    take the factors you mention into account and can present
    enough of a semblance of that information so that the
    ear/brain finds it most interesting and is generally willing
    to suspend disbelief enough to thoroughly enjoy the
    resemblance.

    FWIW, I liked it enough that I am in process (paused,
    actually) of constructing a low cost tetrahedral cardiod
    array and developing sophisticated host DSP transformations
    based on empirical measurement to see if I can come up with
    something that mere people can afford. I think that with
    the DSP assist it can be brought much closer to Gerzon's
    ideal than has been achieved to date and with a much less
    expensive array.


    Bob
    --

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

    A. Einstein
  14. I need to correct what is perhaps the biggest misunderstanding about Ambisonics.

    For some inexplicable reason, most of the people who criticize Ambisonics state
    that Ambisonics claims to reproduce the original waveform over a large listening
    area, then (correctly) point out that this is not possible.

    I've read a lot of Ambisonic literature (theoretical and otherwise), and I have
    never seen anything even remotely approaching this claim. What actually happens
    (and what I think people are misinterpreting) is that you can walk all around
    the listening room without losing the image -- something that conventional
    stereo recording cannot come close to doing.

    I applaud your efforts to come up with a less-expensive and better-quality
    SoundField array. (I own a SoundField mic, and am not really happy with the
    sound quality, which is a bit dark and grundgy.) However, the problem isn't its
    cost, but the violently _negative_ way most engineers view any attempt to
    accurately record sound. If this were possible, they'd be out of job.


    >> Like many people, you're criticizing Ambisonics for the wrong
    >> reasons. I interpret this as a perverse excuse for rejecting
    >> something that happens to work extremely well. And it IS
    >> perverse to deny a system that actually takes into account
    >> how the ears and brain interpret directionality.


    > Then you've interpreted me incorrectly. I loved the sound
    > of Ambisonics at the single demo I heard (at that time I
    > didn't understand enough about it to even note the speaker
    > configuration used for reproduction much less ask about the
    > feed transformations) but I don't like the extravagant
    > claims made for its "correctness" now that I fully
    > understand the theory and practice. I don't think that
    > theoretical correctness is necessasary for a system to do a
    > damn nice job of capturing something that, when carefully
    > reproduced, is very pleasant and plausible. Yes, it does
    > take the factors you mention into account and can present
    > enough of a semblance of that information so that the
    > ear/brain finds it most interesting and is generally willing
    > to suspend disbelief enough to thoroughly enjoy the
    > resemblance.


    > FWIW, I liked it enough that I am in process (paused,
    > actually) of constructing a low cost tetrahedral cardiod
    > array and developing sophisticated host DSP transformations
    > based on empirical measurement to see if I can come up with
    > something that mere people can afford. I think that with
    > the DSP assist it can be brought much closer to Gerzon's
    > ideal than has been achieved to date and with a much less
    > expensive array.\
  15. See, it's good to be stupid. Get's one some answers! <g>

    --


    Roger W. Norman
    SirMusic Studio
    Purchase your copy of the Fifth of RAP CD set at www.recaudiopro.net.
    See how far $20 really goes.




    "Chris Hornbeck" <guyville@removethisaristotle.net> wrote in message
    news:eevfkvkl5qmjgmf15c1qandpqtes6lnsej@4ax.com...
    > On Sat, 23 Aug 2003 15:05:27 -0400, "Roger W. Norman"
    > <rnorman@starpower.net> wrote:
    >
    > > how a single diaphram mic is going to have a charged backplate and
    > >have reasonable sound coming in from the back of the 8.

    >
    > I've never seen one, but imagine the construction to be
    > like a really, really small electrostatic speaker, with
    > porous fixed plates and a charged diaphram between.
    >
    > A side benefit, if the charge is constant, is an inherent
    > linearity missing from conventional single-ended mics.
    >
    > Chris Hornbeck
    > http://www.votetoimpeach.org/
    >
  16. ScotFraser

    ScotFraser Guest

    << Firstly, post processing is always required to tame a location recording to
    be even remotely realistic.

    Post processing is never necessary if the initial recording was done correctly.

    <<Most PA speakers at music venues are mounted parallel to each other, so the
    mic has to be towards the rear of the room to get decent direct sound from
    the horns especially.>>

    If this is indeed the case you are dealing with an improperly set up sound
    system. While this is very likely true in many venues, I wouldn't base a theory
    around bad sound system design.
    Scott Fraser
  17. ScotFraser

    ScotFraser Guest

    << I applaud your efforts to come up with a less-expensive and better-quality
    SoundField array. (I own a SoundField mic, and am not really happy with the
    sound quality, which is a bit dark and grundgy.)>>

    Why not upgrade the existing hardware. It couldn't too difficult to redesign
    the capsule electronics, & even replace diaphragms if needed to get the color
    you desire out of the system. Or do you suspect the darkness & grunge comes
    from the processor? Certainly the analog path there could be brought up to
    current standards.

    << However, the problem isn't its
    cost, but the violently _negative_ way most engineers view any attempt to
    accurately record sound. >>

    All engineers are attempting to (more or less) accurately record sound. I think
    you extrapolate motives a bit much here.

    <<If this were possible, they'd be out of a job. >>

    No, because intentional inaccuracies, such as are brought out by close miking,
    will always be a major part of the art of recording.




    Scott Fraser
  18. James Boyk

    James Boyk Guest

  19. Thanks. I think I've visited them before, but I'm going to look again.

    --


    Roger W. Norman
    SirMusic Studio
    Purchase your copy of the Fifth of RAP CD set at www.recaudiopro.net.
    See how far $20 really goes.




    "James Boyk" <boyk@caltech.edu> wrote in message
    news:bib0ii$sa2$1@naig.caltech.edu...
    > Roger W. Norman wrote: Didn't you use to have a website listed on your
    > signature James? If you've got one, I'd like to visit it. Perhaps
    > you have some of your demo stuff available?
    >
    >
    > Tnx for your interest. I have three websites. Each is fairly extensive.
    >
    > http://www.cco.caltech.edu/~boyk
    > http://www.cco.caltech.edu/~musiclab
    > http://www.performancerecordings.com
    >
    > James Boyk
    >
  20. On a personal note, I'd never try to record any music based on the PA
    speakers being a part of the recording. In my opinion, and I run live sound
    systems, the SR is never as good as the live music from the musicians. If
    you're that far back and getting SR in the recording you need to move up.
    James' speciality is live acoustic sound in world class venues that don't
    have SR. Mine is live from the stage. If your's is live in the room from
    SR speakers then I don't believe it matters all that much how you set the
    mics.

    Sorry, not trying to rag on you. Just not the same thing we're talking
    about. The concept is to be the listener as in someone that can actually
    hear the performance from the stage. Unless I'm getting your post wrong,
    which certainly has been known to happen.

    --


    Roger W. Norman
    SirMusic Studio
    Purchase your copy of the Fifth of RAP CD set at www.recaudiopro.net.
    See how far $20 really goes.




    "Sugarite" <nobody@home.com> wrote in message
    news:MOP1b.7353$q9.450820@read1.cgocable.net...
    > > Somone mentioned a new stereo mike that embodies coincident cardioids

    > crossed at 90 degrees. I find it odd to use this arrangement, since the
    > stereo given by this arrangement is much too narrow, and is also irregular
    > in movement across the stage. This has been noted by others in the group

    in
    > other contexts, and is also shown in the stereo miking demo recording made
    > in my lab.
    > >
    > > On the other hand, what should the mike be instead? If it were

    > ORTF--arguably the best you can do if you're confined to cardioids--it

    would
    > be physically more awkward, and probably more vulnerable to damage. But
    > perhaps 120 degrees would have been usefully better. As long as they were

    at
    > it, though, why not make a coincident, 90-degree pair of
    > condenser....figure-8's? Even go all the way and make single-diaphragm
    > fig-8's, like the Schoeps MK-8.
    >
    > I own a Rode NT4 (which is a coincident cardioid XY small diaphram pair

    like
    > you describe) and use it often for stereo location recordings. Serveral
    > issues haven't been addressed in all the other replies in this thread, so

    I
    > figured I'd start from the top:
    >
    > Firstly, post processing is always required to tame a location recording

    to
    > be even remotely realistic. The widening of a 90 degree cardioid XY pair

    is
    > just one of many processes that must be done, and even though another mic
    > format might be better suited to rendering more natural imaging before

    post,
    > it's a minor issue compared to other factors, one of which is proper
    > rejection. I don't claim to know exactly why 90 degree coincident

    cardioids
    > can offer the best imaging, but I'm going to offer a plausible explanation
    > for the specific circumstances of a live concert, which can also apply to
    > other environments.
    >
    > Most PA speakers at music venues are mounted parallel to each other, so

    the
    > mic has to be towards the rear of the room to get decent direct sound from
    > the horns especially. The rejection pattern of the cardioid XY is such

    that
    > when the stereo image is widened during post, the resulting rear

    information
    > becomes an amalgomation of what was originally mostly side information, so
    > the perceived position of the listener is a lot closer than the mic

    actually
    > was. It's the best of both worlds - the balanced mix, ambience, and
    > frequency response of a mid-rear location combined with the scope, impact,
    > and potency of the front row.
    >
    > Here's an example of this technique:
    > http://www.thetrewsmusic.com/media/mp3/060703-tow.zip
    > The mic was actually about 50' back from the stage in one of my favorite
    > recording venues (Kee to Bala, Muskoka region, Ontario, Canada), and yeah
    > it's rather squashed to let the room ambience add some hugeness too it,

    it's
    > a promotional clip on the band's website...
    >
    > It is NOT the same as placing the mic closer and using a wider

    differential
    > angle. If the mic were as close as it seems, it would not have had the
    > clarity or balance that can only be found within the good dispersion area

    of
    > the PA speakers. A wider differential angle would not allow for as much
    > perceived proximity improvement, and a narrower angle wouldn't offer

    enough
    > side info to work with. A pair of omni's would render a big pile of mud

    by
    > comparison, and figure-8's would slew the rear imaging and leave a gap up
    > front. AFAIK the cardioid XY pattern is the only way to acheive this
    > effectively, probably because the 90 degree angle represents the

    separation
    > between the two independent component vectors of the forces imposed on a
    > single positon in two dimensions, hence the term "XY", much like the

    grooves
    > on stereo LP's. I haven't done enough recording of acoustic performances

    to
    > comment concisely, but there are again advantages to a rear mic placement
    > with widening during post, and so far that process hasn't failed me.
    >
    > I also strongly discourage using separated mics for the differential delay
    > imposed. I've heard the argument to death that it makes sense because our
    > ears are separated and the human auditory system depends on differential
    > delay for imaging, but we're recording for a stereo, not a human auditory
    > system. AFAIK nobody makes a CD player that plugs directly into the
    > cerebral cortex. A stereo and the listener's ears do their part on their
    > own and I see no reason to make special accommodations for this particular
    > aspect. Coincident mics pick up the stereo image found at one position,
    > then a properly configured stereo allows the listener to assume that
    > positon. It is impossible for a listener to be in two positions, and also
    > impossible for a stereo to reproduce two postions, so having mics in
    > different positions generally makes about as much sense as putting legs on

    a
    > car.
    >
    >

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