Conference cookie::notes$archive:cd_v1

    Sounds like a solution to a non problem.
    
    Either the disc has been made right, in which case you don't need
    it, or it hasn't, in which case return it for exchange.
    
    Barry, in marlboro,mass.

    
    I recently bought a CD from the CDSWAP notes file.  I was wondering
    what that thing was on the disk.  I haven't really seen that it
    makes any difference in the sound.  The disk hasn't had any skips
    but none of my other disks have either.  I agree with Barry in
    Marlboro. > It does sound like a solution to a non problem.<
    
    Tim

    
    Interesting how this "perfect" medium needs some assistance from
    damping rings and lens cleaners.  
    
    More interesting is how consumers bought the perfection story and
    now are swallowing the "this will make it perfect again" story....
    
    

    
    I saw the damping rings at Natural Sound and being curious decided
    to try them. It cost 5 bucks for a starter kit which comes with
    5 rings and a rubber piece that allows you to center the rings on
    the disc. I have some discs that sound terrible, very harsh and
    I heard that the rings may help. 
    
    Well, In MY opinion there was a VERY noticable difference. There
    was a definite improvement in the sound quality. I think the rings
    may be more obvious on certain discs then on others. At least that
    has been my experience. I believe the reason they are supposed to
    work is that they lessen the vibration of the disc, which is causing
    errors. I'm not any kind of authority on CD theory but
    possibly there is an improvemt in sound quality when everything
    is free of vibration. I know the turntable folks go to all lengths
    to stop vibration.
    
    I know that there is alot of hype in this industry but before we
    all start declaring something is a fraud we could at least try the
    thing out. Five bucks is not going to break most of us.
    
    Just an opinion.
    
    Mike

    Does "applied to the outside edge" mean exactly that - a metal ring
    around the edge, rather than on the top at the edge?  (I've never
    seen these.)
    
    I'd be skeptical for two reasons:
    
    1)  How does it attach?  If there's any kind of adhesive, that adhesive
    might attack the lacquer on the top surface and kill the disc
    permanently over time.  If it attaches mechanically, might the process
    of attaching it break the seal that keeps air out of the CD and
    cause the aluminum to corrode?
    
    2)  Many players, especially portables, have *very* little clearance
    around the disc.  Might this not make the disc rub somewhere?  (Some
    people complain that their portables rub discs even without these
    rings.)
    
    Maybe it works, but I have no problem that desparately needs solving.
    I'd sure want to hear a lot more about this before trying it - and I'm
    inclined to let someone else be the guinea pig and risk their CDs, not
    mine.

    B
    
    
    
    
        
    B 
    

    
    
    The rings are a rubber type material that have an adhesive on one
    side. They are applied to the label side on the outside edge . I 
    don't know if the adhesive can eat away the plastic. You would hope not.
    
    I have a Sony CDP510 and don't have any problems playing CDs with
    rings. I have heard that some machines won't take them. Also, they
    say that if you put them on don't try taking them off because they
    won't come off without damaging the CD. 
    
    Mike

    Damping rings are pure hype.  What comes off the disk is a string of
    numbers.  In the case of errors, there is ECC to correct any but
    the most grievous of problems, and a disc that is so bad as to not
    be ECC correctable over the entire disk is outside the manufacturing
    tolerance standards by orders of magnitude.  Repeated tests by
    audio magazines have shown that uncorrectable errors in discs are
    almost unheard of.
    
    If the error is correctable, it's PERFECTLY correctable.  Damping rings
    aren't going to make any more difference on your disks than if you
    hung them from your ears.
    
    					Steve

	Actually those rings will improve the sound of a CD in
	some cases.

	What can happen is vibrations in the player can cause 
	UNCORRECTABLE read errors.  This is do to the momentatry
	speed changes when these vibrations accur.  These 
	UNCORRECTABLE read errors usually manifest themselve by
	Very brief dropouts of sound.  In many cases, the dropouts
	will make the sound coming out of the player sound harsh.
	If the error is a bigger one, you may actually hear the
	momentary dropout.  But again, it is usually too fast
	to hear other than the "by-product" of harsh sound.

	The rings add mass to the disk which will dampen out some 
	of the smaller vibrations.  This will produce a cleaner
	sound.

	Those rings won't fix all of these problems but they do
	work.  May manufacturers of disk players know about this 
	problem and go through great lengths, in some cases, to
	try and isolate the disk spindle from external vibration.

	That brings up another point; CD players don't like even
	small vibrations.  These small vibrations such as loud
	playing levels from near by speakers can cause read errors
	which may show up as making the CD sound harsh.

	Car CD players are very hard to design because of this 
	problem.  That is one of the reasons they cost more.

    Sorry, I don't believe it.  Repeated tests show that uncorrectable
    errors on normal (non-defective) disks are extremely rare.  Most
    causes of uncorrectable errors are damaged disks, and no amount of
    "damping" will help that.
    
    As for car CD players, the problem is that large vibrations cause the
    player to mistrack.  This involves jostling of the pickup sled, and
    again, vibrations of the disk itself are meaningless.
    
    Go ahead and stick these things on your disks if you want - they
    look pretty.  But there's no evidence that they actually do anything.
    
    				Steve

    
    Steve,
    
    Two questions.
    
    Where do your repeated tests come from ?
    Have you ever heard a demo of the rings ?
    
    Mike

    
       To add to this discussion,
    
       I have to agree with Steve (-.2) on the hard, uncorrectable
    error rate. Now I don't know about Steve's data. But, mine is from
    the RQT (Reliability Qualification Test) that Digital ran on the
    RRD50. The RRD50 is the very first CDROM player built by anyone
    that I know of. We ran about 40 drives for about 6 months with a
    specially designed test disc that had known data patterns, and forced
    errors imbedded into it. The occurance of the errors we are talking
    about is very rare. I was on the RRD50 project from its conception.
    I tend to agree with Steve, a damping device will not make hard
    uncorrectable errors go away. I can't think of much that would.
    The ECC on the drives is quite good too. 
    
    	"Digital has it now,......and it's been in test for the past
            3 years!" What a distribution medium for software!
    
    	John
    

    This is a *bad* subject for an audiophile-type argument, because
    we're talking about a digital medium.  Whether the rings help
    or not can be easily verified if someone has the test equipment.
    
    The argument *for* the rings is that they decrease the number of
    uncorrectable errors (presumably caused by disk vibration, in turn
    presumably caused by imperfect disks).  Since CD decoding chips
    *know* when they get uncorrectable errors, this data can be 
    collected.  Build a device that counts these errors (some CD
    decoding chips have an output that fires when such an error is
    detected, I'm told).  Get a few hundred disks.  Play them a bunch
    of times both with and without rings attached (to the *same* disks).
    
    Tally the error counts.  If the rings help, it will be manisfest
    in consistently lower error counts for the disks with the
    ring, as opposed to the *same* disk without the ring.
    
    To my knowledge, none of the damping-ring vendors has published
    the results of such a test.  My cynical side suggests that this
    is because no such test has been done, and the folks selling
    the rings *are* selling snake oil.  It *might* actually work,
    but I doubt that the folks selling the rings know if it does
    or not, and I'm pretty sure they don't really care so long as
    you buy their product.
    
    		George

    
    
    	I've read recently that it is common for the error correcting
    mechanism in CD players to make up to 20 corrections/second in normal
    playing. I dont know if these are "single bit" or "single word"
    corrections, however.
    
    	Since the 44.1 Khz sampling frequency is within a knat's *ss
    of the Nyquist frequency, a few words missing and the corresponding
    interpolation could make for a harsher sounding high end, I think.
    
    	Most CD players use a stepper motor, I'd bet, for spinning the
    disk. This would afford easy digital control over the motor speed,
    with the rotational mass of the disk and spindle integrating the
    pulses into a smoother motion. Massing up the disk makes it a better 
    integrator and will give a smoother, more consistant angular velocity.
    Of course, since this is a digital system, as long as the specified
    d2@/dt is met, any improvement has no effect. Do we assume that
    this is met;
    			- all of the time, for any disk?
    			- most of the time, for most disks?
    			- just barely, with your best disk?
       
    	I dont know.
    
    	*Possibly*, this could effect the error rate coming off the
    disk and in turn, reduce the number of "big" interpolations the
    correcting circuitry would have to make. However, what happens if
    you dont center this additional weight *perfectly* and cause this
    disk to be out of balance? Ruin the disk, apparently.
    
    	Perhaps they'll give some sort of digital display for the
    relative "quality level" of the playback, expressed in terms of
    the number and kinds of corrections the player had to make to deliver
    the sound, on future machines.
    
    	Joe Jas 
         

   re:.13
    >   Since the 44.1 Khz sampling frequency is within a knat's *ss
    >of the Nyquist frequency
    
    I'm not sure I understand what you mean here.  The Nyquist frequency
    is always half the sampling frequency.  I think you may mean the
    *Nyquist* frequency is only slightly higher than what the (best)
    human ear can detect, yes?
    
    >, a few words missing and the corresponding
    >interpolation could make for a harsher sounding high end, I think.
                              
    I thought that the ECC was successful in correcting errors, not
    merely interpolating to find the missing values.  If the error rate
    is low enough, the code should be robust enough to completely correct
    for soft errors.
    
    >	Most CD players use a stepper motor, I'd bet, for spinning the
    >disk. This would afford easy digital control over the motor speed,
         
    I'd bet not; I would assume they use a frequency servo-controlled
    motor, and spit the data into a circular buffer.  When the buffer
    starts to get full, slow down the disc a little, when it gets empty,
    speed it up a bit.  You know, like negative feedback.  I don't think
    there's a need for the ability to specify the motor speed exactly,
    just to make incremental changes based on the output rate of data.
    
    Sorry, I'm ratholing the subject I guess.  But until someone performs
    the test that George suggests, the ring damper arguement is probably
    moot.
    
    		Steve
    

    I doubt that these "damping rings" do any good at all -- but I don't
    think that the number of uncorrectable errors found by a CDROM drive
    is the right statistic to be measuring.  To the best of my knowledge,
    the CDROM format employs more error correction than CD Audio format,
    with the rationale being that errors in audio output tend to be less
    noticeable than errors in stored computer programs and data . . .

    
    
       Here we go with a real technical discussion the CD/CDROM formats...
    
    
    	Let me see if I can shed some light here;
    
    	o CD players do realtime ECC for correctable errors
    	  encountered while reading the disk.
    
    	o The only time an interpolation is done is when the ECC
    	  can't correct the data.
    
    	o The ECC on a CD is extensive, the data is scattered over
    	  a 2,000 bit area on a given "track", and the ECC can correct
    	  multiple symbols in error. A symbol is not a bit, or a byte,
    	  or a word. It's just a very specific collection of bits.
    
    	o DEC's RRD products have additional layers of ECC built into
    	  the data format we put onto the disc, DSA defines the way
    	  this is done.

    	o The speed of rotation is determined by the data coming off
    	  of the disc itself. It is a complex set of feedback mechanisms
    	  that keep the disc spinning at a rate sufficient to keep the
    	  right number of bits coming in. PLL's etc...
    
	o Uncorrectable errors are rare.
    

    
    I could go on and on about the technicalities of a CD/CDROM player.
    Basically the 2 are the same. Just that with the CDROM the error
    signal output goes to the system for error recovery, not to another
    chip to interpolate the sound for you.
    
    My source for most of this is the RRD50 Tech. Man. (EK-RRD50-TD)
    
    	John
    

    There's an article in today's Boston Herald on Disc rings.
    
    Stig

    For what it's worth....
    
    Many folks here are confusing interpolation and error correction.
    The former loses information, the latter does not.
    
    
    And, it doesn't take a golden ear to hear interpolation.  I've got
    the killer cold thingies invading my ears right now, and the
    antibiotics are taking their sweet old time dealing with the
    hostile forces.  Yet I can assure you, that if I did a listening
    to two players *today*, one interpolating, the other not, I'll quickly
    point out which one is being not nice.
    
    
    You see, every once in a rare while, my CD player goes into some
    sort of resonance.  Don't know why, but the disc and/or servo will
    "hummmmmmmmm" audibly.  Sounds a little like a very quiet glass
    harmonica.
    
    
    When this happens, the sound is awful.  That's because bits are
    not being corrected by the ECC, but are being interpolated.
    
    Sorry, I'm not into the latest golden ear rhetoric, but oh, lets just
    say that the sound stage is compressed to the zeroth dimension, beyond
    blured at any rate, ah, there is a stealiness and edginess to the
    sound, and, hmmm, just for good measure, it sounds discrete.
    
    In english, all the above nonsense means that the sound is awful. 
    
    
    Shortly, it will go beyond just awful, to horrible.  There will be
    quite audible drop offs of sound, where even interpolation gives
    up and says "Sorry, I'll just be quiet, for I haven't a clue".
    
    Finally, the CD player begins to lose the ability to track the disc
    at all.
    
    
    When this happens, a second disc layed on top of the disc that I
    wish to play "cures" the problem every time I've tried.
    
    But I don't much wish to treat my discs or my player to such
    attrocities, so I've not tried that very often.
    
    Instead, I HOWL an incantation or two or three (the FCC would not
    approve) and take the disc out and put it back into again.
    Repeating several times often "solves" the problem.  I'm not at all
    sure if it's the incantations or the replacing the disc that does the
    trick, not having done a scientific controlled study.  Perhaps both are
    required. 
    
    Oh, at first I thought it might be a problem with only certain discs.
    But this does not seem to be so, it is quite quite random.
    
    
    So, having said all that, it is *possible* that such rings actually
    do do something.  I, however, would not spend the money on such
    nonsense.  I would instead spend the money on getting a new CD player
    with a more stable servo system.  Or at least one with oxygen free
    plastic.  I mean, who wants rusty plastic?
    
    (Finally, there's a nodename called KANE::?)
    
    								-mr. bill

    Re:1472.16
      John...I have often wondered what technology is used to make the "
    master"disk's grooves.I.E. what is the distance between the grooves on
    the cd and how do they make the master.I assume that the copies are
    "pressed" from the master copy.Do you know the technique???
    
    
    Marc H.

    
    Marc,
       Funny you should ask! When I was working on the CDROM projext
    we got a tour of the Polygram plant in Germany. The mastering 
    facility is seperate from the pressing plant. The mastering plant
    we say looked much like Hudson does. Clean rooms, bunny suits, etc.
    The masters we worked with for CDROM applications were very close
    to the mastering set up for normal CD's. They have a VERY precise
    laser set up with VERY precise servo control. The master is written,
    read and verified for quality standards. If I remember right that
    implies a low number of ECC, and no uncorrectables. The master is
    then pressed to make fathers, the faters are then pressed to make
    mothers, the mothers are then used to make discs, for a while. At
    the end of the useable like of the mother they toss it and replace
    it with another mother to then press more CD's for us consumers.
       The whole process was then made more difficult by DEC when we
    built a VAX frontend to master discs for data use. We had to cut
    into the datat stream a bit to get the data in the format that we
    wanted. Philips I believe licenses this mastering set up based on
    a VAX for resale. Yea, VAX's are used to master some CDROM discs!
       The process was very interesting. It was also a lot of fun trying
    to develop the process to get CDROM's mastered so that the FOO.EXE
    file didn't get interpolated when VMS read it! 
    
    	What's a bit between friends!!!
    
    	John

    This is slightly off the subject, but I recently got a free TELARC
    sampler for purchasing a pair of Sennheiser headphones.  Playing this
    disc has been ear-itating, as there seems to be excess vibration (the
    disc visibly wobbles, about 1/8"), and this leads to a harsh, low
    volume resonance.  Perhaps this is the sort of problem a disc ring
    solves. If I had actually purchased the disc, I would return it, but it
    seems petty to complain, especially since the drive to the place of
    purchase would probably cost more than the value of the disc. 
    
    Jim
    

    RE 1472.20
    John,thanks for the info! Do you happen to know the spacing between
    tracks?
    
    Marc H.

    
    Marc,
       The track pitch is 1.6 microns on center, with a bit width
    of 1.0 microns. If I remember correctly...
    
    	John

	I've got a CD that drives me crazy. It must be placed just
	so or otherwise I get 'dropouts'.  I thought for awhile that
	I had a defective CD and was going to send it back for
	replacement but I had a few times later and it was perfect.
	After that someone played and behold a couple of dropouts
	occured but not in the same places. This is the only cd that
	acts that way. I am wondering if the CD is so lite that it
	does not seat properly and supposedly that is what the rings
	do.

    'Back in the old days', I remember taping pennies and nickels to the
    tone arm of my record player to "improve" tracking.  It solved the
    tracking problems for a while, but eventually, all my records were
    were ruined.  I ended up buying a new turntable.

    I suggest that the 'CD rings' are a similar type of "solution" with
    possible hazards, which only masks the real problems.


    							-Paul