Re: 'Sound recording' *and* '3D sound'

[P3D Bill Costa - NIS/CIS - University of New Hampshire <Bill.Costa@xxxxxxx>]

    In a recent posting, Michael Kersenbrock <michaelk@xxxxxxxxxxxxxxxxxx>
    wrote (in part)

>  Jokes aside,  it seems that any one of the surround sound variants
>  (discrete multichannel, dolby pro logic, etc) would work very nicely 
>  in conjunction with projected 3D visuals.  Anybody try that ?

    and Adam L. Beckerman  <adam@xxxxxxxxxxx> also mentioned...

> I am working on something now in TrueSpace, a "3d" modelling 
> software, where I plan to incorporate 3d sound.  I will probably 
> record the sound in stereo, and bring it into my sound software 
> called Cool Edit by Syntrillium software (limitware that can be 
> unlocked for $50 I think -- www.syntrillium.com).
  
    Well there is old technology that can be used to create quite striking
    3 dimensional sound.  The recording technique is known as binaural (in
    contrast to stereo audio).  An advantage of binaural is the playback is
    very immersive with sounds apparently coming from all around you. 
    Well, almost (see below).  It is also a nice technique where  you have
    little control over mike placement.  It can also be very inconspicuous
    way to record audio, an advantage in some situations. ;-)  Of course
    taking 3D photos inconspicously is a whole other matter!  The
    disadvantage of binaural is that for the effect to work, the recording
    must be played back using headphones, not loud speakers.  For my 3D
    video project, I want to play back the 3D video using a head mounted
    display so this is not a problem since headphones are part of the unit. 
    But for projection of 3D slides, it'd be a real problem to have to hand
    out glasses *and* headphones!
     
    So what is binaural?  Glad you asked.... ;-)
 
    Here is a short article I wrote for some non-technical friends about my
    binaural records.  It's pretty basic, reviewing stuff about mono and
    stereo, which you no doubt already know.  Just skip down to the
    *binaural* part at the end.
 
    							Later....BC
 
- - - - - - - - - - - - - - -8<- - - - - - - - - - - - - - - - - - - - - -
 
    This tape was made using a recording technique known as *binaural*. It
    may be played on any cassette sound system, monaural or stereo.  It
    will sound best, however, when played over stereo headphones.  Thus an
    ideal way to listen to this tape is to use any `walkman' type stereo
    cassette player, using the standard, light weight, open-air headphones
    that are commonly supplied with these units.  When listened to in this
    way, I think you'll notice a greater degree of realism in this tape
    when compared to a convention stereo recording.  That's all you need
    to know to play this tape, but if you're curious about the technical
    details, read on.
    
    There have been a number of different recording techniques developed
    over the short history of sound recording.  The oldest of these is
    recording with a single microphone, for playback through a single
    speaker.  This is what is generally termed as *monophonic* or
    *monaural*.  
 
    At it's simplest, *stereo* recordings are made using two microphones,
    separated at some distance from each other (say six to ten feet).  Each
    microphone picks up a slightly different version of the sound being
    recorded.  For example, if the left microphone is the nearest to the
    trumpet player, both microphones will record the sound of the trumpet,
    but the apparent volume of that instrument will be louder in the *left*
    channel than the right.  When the recording is played back through a
    pair of  speakers,  separated from each other as the microphones were,
    a *stereo image* is created.  In our example, the sonic image of the
    trumpet will be towards the left.  A good stereo recording should allow
    you to close your eyes and easily point to each instrument's apparent
    location, just as if it were a live performance.
 
    Stereo recordings can also be played through stereo headphones, of
    course.  The effect, however, is quite unnatural. While the stereo
    image still exists, or is even somewhat enhanced, the sound does not
    project itself in front of you.  Instead the music seems to be located
    inside the middle of your head.  Still, a stereo recording with
    headphones sounds much better than monaural, the sound is more open and
    spacious, and the individual instruments can still be easily
    distinguished and located within the stereo image.
 
    *Binaural* is a recording technique designed specifically for playback
    using headphones.  Like stereo, binaural requires a separate left and
    right channel.  When the recording is made, two microphones are used,
    but the separation between them is only a few inches.  In addition,
    some sort of barrier is placed between the two microphones to help
    isolate the sounds being picked up by each. In fact, a common technique
    is to use a life-size mannequin's head, with a microphone located
    within each ear.  
 
    For this recording, I used a special microphone arrangement that I
    built specifically for this application.  It consists of a pair of
    glasses (I use safety glasses since my eyes do not need correction). 
    Attached to each leg is a tiny, hi-quality microphone located close to,
    and pointing at, my ear.  The cord is attached to the leg and dangles
    down, looking just like the `retaining cords' that are so popular on
    sunglasses now.  This technique provides the separation needed while at
    the same time, remains inconspicuous.  (I just have to remember not to
    talk while wearing and recording with this setup, and to keep my head
    always facing the music.)
 
    Binaural recordings are rarely available commercially because they
    sound somewhat flat and monophonic when played through conventional
    stereo speakers.   But when played back using ordinary stereo
    headphones, the effect can be quite striking.  Sounds coming from
    center stage may still tend to image in the middle of your head, just
    as with stereo.  However, sounds  to the left and right, as well as
    sounds from behind, should sound very natural and realistic in their
    placement.  [This is the effect that *four channel* and *surround
    sound* systems are trying to duplicate; sound images that can be
    localized not only from left to right, but also from front to back.]
 
 
    This particular recording was made from within the audience of a
    live event.  With a normal monaural or stereo recording, the
    surrounding audience noise would have tended to obscure the music or
    speaker.  With this recording, however, you should be able to close
    your eyes and easily imagine yourself being there.
 
    
    
    Bill Costa
    14-JULY-1992


------------------------------