-=> Quoting Drew Hohmann to Cameron Hall <=-
 DH> good point here.  I thought that the CD player spun the disc at a
 DH> constant rate, like a record player. Though now you have me
 DH> confused.  A record player rotates at a constant rate, yet even
 DH> though the inside edges and the outside edges travel at different
 DH> speeds, their is no difference in pitch between the outside and
 DH> inside edges.  (Meaning if you had a 33 record playing at 45rpm, 
 DH> it'd be higher pitched, yet even though the edges are traveling
 DH> at different speeds, it's the same pitch throughout the record). 
 DH> Seeing how it's summer, my brain isn't working the way it should,
 DH> so can you please explain this?
        There are two types of discs and ways of reading discs, be
they LP, Laserdisc, or CD.  You have CLV (Constant Linear Velocity)
and CAV (Constant Angular Velocity).
        The LP is CAV.  The platter rotates at a constant angular
velocity.  The information is recorded this way so playback reproduces
it the same way it was recorded.  I'm not sure of the efficiency of
this method for LPs since groov width can vary depending on the
compression for bass and what not, I believe (someone correct me if
I'm wrong...I'm no expert on LPs).  Maybe someone knows about
efficiency here.  Although even if CLV was more efficient, I think
you'd have some trouble varying the speed of the turntable while
mainting accuracy since the information is directly on the disc in
wave form.
        The CD is CLV.  The disc is spun at a variable rate to fit the
maximum amount of data possible onto the disc (since obviously the
outer diameter is larger than the inner and so more data can be fit
around it and since the outer edge of a disc is moving linearly faster
than the inner, it must be slowed down to maintain the same linear
data rate).  And since it's digital and can be buffered, it's not
important to have *exactly precise* reading speeds.  If CDs were CAV,
either the CD would have to buffer ahead all the information it's
reading (because it would be reading data faster and faster as it
approaches the outer edge), which would require vast amounts of RAM or
it would have to space the pits further and further apart, which would
waste space.
        Laserdiscs come in both types.  CAV laserdiscs store 1 image
per revolution.  To get a freeze frame picture, the laserdisc merely
keeps the laser on the same part of the disc and keeps it moving at
the constant playback rate.  Thus, it simply displays the same picture
over and over again, giving the illusion of a freeze frame.  It's also
easy to do slow motion/fast motion effects in forward or reverse
because regardless, there is always 1 video frame per revolution.  The
laser merely tracks back and forth at varying rates to accomade
varying slow/fast speeds.  It's smooth as silk.  The bad part is that
the playing time of CAV discs is limited to 30 minutes a side.
        CLV laserdiscs have the advantage of storing 60 minutes a side
(double the time of CAV) by varying the angular speed to maintain a
constant linear velocity which in normal playback works just fine and
makes far more efficient use of the outer parts of the disc.  However,
if you try to use that freeze frame effect described above, it would
have part of another frame (possibly more than one frame the further
out you go) in the picture as well since data is crammed onto the disc
as much as possible.  Therefore, those advantages of CAV are lost.
More expensive players use digital memory to store a freeze frame and
perform computer animation style buffered slow/fast motion (usually
lower quality than a CAV disc, however).  
 * AmyBW v2.14 *
... If Q were castrated would he become ... O?
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