STUDIO BASICS IN BRIEF

                                                 
    Studio isolation depends on several things, some obvious, some not.
    To state the first obvious factor, instruments are directional,
    mikes are directional, and instrument amplifiers are directional.
    Again obviously, the directionality of these three can be used in an
    intelligently designed setup to keep the sound of one instrument
    out of another's mike.

    The second gimmie is room treatment. There are three ways to go wrong
    on this, and two of them are common.

    The most prevalent treatment problem is the stuff used to deaden the
    room. So many studios have put cheap carpet on every available surface
    that it has come to be regarded as a good thing to do. In fact, it is
    a terrible thing to do. Carpet, drapes, acoustical tile, and thin
    Fiberglas all share the same characteristic. They don't absorb bass.
   
    They do absorb top end. Some better than others. Carpet and drapes
    absorb about one-fifth as well as Fiberglas, and are many times more
    expensive. Cheap acoustical tile absorbs very well, but only in the
    middle of the spectrum. Fiberglas and Sonex absorb to the maximum,
    but except in suspended ceilings, thin fuzz drops dead below 400 to
    500 HZ and Sonex is unthinkably expensive for ceilings.

    So unless the studio walls are so flimsy as to vibrate with bass and
    send it outside, the result of using a lot of thin studio treatment
    is a working space that ranges from boomy at bass frequencies to an
    absolute grave on top. The sound of the room is reflected in the
    microphone isolation characteristics, with the low end sound falling
    through every mike in the place, and a dry, sterile top end.
   
    Needless to say, it's very hard for musicians to work in a room like
    that as they can't hear each other bouncing off the walls. All boom,
    no tinkle.
   
    Overtreated, dead rooms are a frequent problem, and a near inevitable
    result of using thin acoustical treatment, as too much of it is usually
    laid on in an attempt to pull down the room bounce at medium
    frequencies.

    The third standard problem is, of course, insufficient treatment and a
    room that is too live to yield adequate isolation.
   
    Which brings up the subject of how much treatment is needed in a studio.
   
    Interesting, as not only is there no simple answer, there has been
    virtually no valid material published on the matter.

    The difficulty here lies in the fact that the amount of treatment
    for a studio varies, but not directly, with the size of the room, so
    how much is a complex calculation. However, the result of the treatment
    can be stated in reasonably simple terms, and the amount can be arrived
    at by experiment.

    First, the result. A vocalist needs a minimum of about 26 db isolation
    on mike to get decent results, as normal limiting eats 10 to 12 db of 
    the available margin.

    Other instruments should therefore die away by at least that much
    before hitting the vocal mike.
   
    Simple distance won't do it, as a performance room must be at least
    somewhat live so the players can hear each other. Anechoic chambers are
    out for recording.
   
    If there is sound bouncing around in a room, the bounce will at some
    point be as loud as the sound source that created it.
   
    That point is called the critical distance, and the Dc of a sound
    source is a statement of how far it travels in a room before it goes
    constant volume. Dc varies with a number of factors including the
    directionality of the source but, as rhythm section instruments have
    about the same directionality as voice, a general treatment can be
    made for rhythm and vocal isolation.

    The treatment needs to yield 26 db or better of die off before the
    source goes constant volume. Sound dies off by 6 db per distance
    doubling until the Dc is reached, with the last figure a 3 db point.
    Therefore, assuming a mike to mouth distance of six inches, 1ft=6db,
    2ft=12db; 4ft=18db; 8ft=24db, and as the last figure adds only 3db,
    a voice Dc of 16 feet adds 3 db more for 27 db of acoustical loss at
    that figure.
   
    You can live with less, as little as 10, but it's not quite
    satisfactory. 12 is definitly OK for general work, and usually used,
    but 16 feet is just bloody wonderful, as you can put a vocal anywhere
    in the room, and allows the mixer to do anything he(she) wants instead
    of the room's dictating all kinds of weird stuff to keep garbage out
    of the mikes.
   
    That's 16 acoustical feet, not straight line, and unless you have a
    low live ceiling, pretty easy to set up.

    To find the amount of treatment necessary for a given room, acoustical
    math is handy if you have it, and available either in a book titled
    SOUND SYSTEM ENGINEERING by Don and Caroline Davis published by Howard
    W.Sams, or in the program on this site.
   
    Otherwise, just measure the room's Dc for a human voice. This is done
    by walking toward someone in the middle of the room while chanting one
    one one one, test, oom, or whatever turns you on as long as it's
    constant in volume and tone.
   
    The listener will hear the talker at constant volume until the room's
    Dc is reached, at which point the talker will become suddenly and
    obviously louder.
   
    Passing thru the Dc a few times in each direction will nail it down
    pretty good, and the trick of using a voice for this is better than
    it might seem at first blush. For one thing the equipment (none) is
    readily available.
   
    For another the system works in any language, and the results can be
    'phoned in. Mostly,however, it checks the room at about 100 Hz, where
    bad rooms go live, and yields remarkably accurate results as a result.
    Clapping one's hands while looking wise and murmuring hmm and aha is
    much more impressive, but as handclaps and the like normally trigger
    the ear well up into the midrange, it's not uncommon to clap out a
    room at one second and find that it's three or more at voice
    frequencies.
   
    Finally, it is a simple fact that rhythm instruments were designed
    to work with the human voice, and it is rational to set up a room
    around that centerpiece.

    Studio design per se is dealt with in some detail elsewhere in these
    texts but in passing it should be pointed out that isolation is
    mostly a function of Dc, and getting a voice Dc of 12 to 16 feet in
    a room with less than 10,000 cubic feet of volume produces a room
    so dead as to be damn near impossible for musicians to play in.
   
    Generally, small rooms have big problems and vice-versa.

    Some less obvious isolation factors include proximity of sound
    sources to walls and instrumental volume.

    The first is easy. Don't build or set up a studio with instruments
    within 4 to 5 feet of a wall. The wall will reinforce the sound
    just like any theater back wall, and you'll hear it on every mike
    in the room.
   
    Taking the above one at time, room volume, in cubic feet, puts an
    absolute limit on how much instrumental volume, in db/spl, the room
    will hold without creating problems. This limitation can produce some
    astonishing situations.
   
    Some years ago, the writer tried to record an operatic soprano in a
    livish 9000 cubic foot room. And failed. The lady produced so much
    sound on her loud notes that she loaded the room, and every loud note
    distorted the mike, as it heard her voice from three or four directions
    at once. She turned a nice little studio into a horrible echo chamber.
   
    The session was moved to a bigger room, worked fine, and the lesson
    remembered.
       
    There is probably a firm rule for ceiling height, but I haven't seen
    it. So to make a rough estimate, for standard instruments and normal
    seating, a live session studio should have a ceiling height in the area
    of 14 to 20 feet. It does not follow that a low ceiling ruins the sound
    but to get a reasonable volume of 12 thousand cubic feet or more, you
    need a whole lot of floor space with a low ceiling.

    Low ceilings work fine, but place a lower limit on the number of people
    that can work in the room. Additionally, the room volume works against
    total instrumental volume, so one can pack strings in like sardines,
    but 20 brass or three 200 watt amps can be a disaster. The room volume
    versus instrumental volume effect may account for the fact that small
    garage studios seem to have less trouble than small basement studios.