Conference cookie::notes$archive:cd_v1

Of course, by "writing area" I mean the printed stuff on the non-data side.

If I understand the process of pressing CDs correctly,
liquid polycarbonate is poured over a glass master and
then peeled off.  It is then coated with aluminum and
then covered with a protective layer of shelac (or some
plastic).  The shelac side is the nondata side.

It would seem that you could make a shelac sandwich
on polycarb bread to make a two sided CD, but I think
that there might be a problem aligning the two sides.
[Apparently it's pretty tough to punch the hole in the
right place to start with.]  I also think that the yeild
of good CDs made by this process might be substancially
less than one sided ones...

Other thoughts?
R.

    In theory, it's possible - look at LV discs.  But in practice the
    disc would end up too thick - the label is printed just above the
    information layer.  To add the protective coating on the other side
    would make the disc too thick.
    					Steve

    Not only would it double the thickness of the disc, but you could
    no longer have a label on the disc (unless it was some sort of
    translucent ink that didn't affect reading that side.)  Also, they
    could have put twice as much music on ONE side if they had not bothered
    to put those extra bits for "later use" in with the music, which
    no one (to my knowledge) has made any use of to date.  (Only about
    35% of the disc stores music).  There's probably not much of a market
    for 144 min. discs anyway...
    
    	Steve

    What "extra bits for "later use""??  Maybe the extra bits could
    be used for the copy protection (if we MUST have that - I don't
    tend to make copies of my CDs anyhow, let alone sell them to other
    people) instead of mangling my music??

    The extra bits on CD's were originally designed to hold video images
    along with the audio tracks.  My player even has a "subcode" jack
    to tap into the extra bit.  It was thought that manufactures would
    produce a "subcode" to TV adapter to allow you to look at the video
    images --- motion pictures, liner notes etc.
    
    As it turned out, there wasn't quite enough extra bits to produce
    a high quality video image.  Most people lost interest.  If I remember
    correctly, there is approximately 1Gb of reserved-for-future-use-must-
    be-zero space locked into the architecture of the CD.
    
    "Subcode" is the father of the new CD-V format.
    
    
    						-Paul
                              

The subcode wouldn't be useful for copyguard, since it isn't in the information
stream.  It wouldn't get to the recorder, so it wouldn't activate the copyguard
circuitry.

/john

 re .5 

>    be used for the copy protection (if we MUST have that - I don't
>    tend to make copies of my CDs anyhow, let alone sell them to other

Well, I make copies of my CD's all the time. And I don't want to not be
able to migrate to the next generation (ie DAT) just because some
music industry jerko's are afraid I'm going to bust their business !

I think they're all just PO'd because today we don't have to buy a copy
in each and every format (LP/CD at home and/or tpae in the car...). I like
the flexibility I have today and I want to keep it in the future.

Peter.

    re: .7
    
    AH!  But what if the CD player detects the bits and IT shuts off? 
    I know, this would not prevent duping from old CD players to new
    RDAT recorders, but still, does this seem too logical to ever fly?
    
    David.

re .9

If the CD player detects the bits it shuts off?

Where are the smiley faces?  That would be a really useful player!

Let's not turn this topic into another copyguard discussion; there are already
three others.

/john

    re:.10
    
    I'm almost afraid that this will be the next attept on the part
    of the recording industry. After all, if the things won't play,
    we can't copy, right?
    
    --- jerry

>    Also, they
>    could have put twice as much music on ONE side if they had not bothered
>    to put those extra bits for "later use" in with the music, which
>    no one (to my knowledge) has made any use of to date.  (Only about
>    35% of the disc stores music).  

As long as the topic has come up, is there an easily obtained technical
spec for CDs, just to satisfy those of us with a theoretical interest
in things?  Are the CDROM specs applicable to audio discs?
How different are the CDV specs (short audio discs that do include video)?

- tom]

    re:.12
      Note 549 has some specifics on the encoding...
    
    -Steve

    re: .10
    
    WHAT THE HELL *WAS* I TALKING ABOUT?   Gees, sorry John.  Guess the
    old brain went to lunch!  What bothers me most is it sounded SO
    logical at the time!   :-)
    
    David_who_needs_a_vacation_like_nobody's_business.

    
    Re: .10 & .14;  look at the bright side; no play - NO background
    noise to worry about....