Where is CD data physically?

[Document Version: 1.00] [Last Updated: Jan_13_1995]

Author: R. C. Lacovara
E-Mail: lacovara@ollie.jsc.nasa.gov
Version: 1.00
Date: 13 Jan 1995

Warning: Flame bait below. Please don protective humor hardware...

Auxilliary Warning: Do not try these techniques at home. A rampaging Audiofile might destroy your collection of the Best of the Sixties. Further, if you intend to bait Audiofiles in their home, keep your back to a door. That way, if boordom causes you to lose conciousness, you might fall out of the range of the monologue, or even make a stumbling escape.

I had a ton of fun when I first got my beloved Sony ES-660 CD player with matched 1% analog 17th order Chebyshev filters and revolving chrondronomos and hyperspace distringulitrix and other expensive features you can't hear by the following experiment:

Get one of those demo disks or Laurence Welk or country & western and have fun with a marker pen. Draw on the aluminum side and you will find that ol' Reed and Solomon did a good job: it takes a lot of obscuration to screw up the disk playback. Use a water soluble marker, unless you don't like the disk.

Radial lines have to be really thick and frequent. Circumferential lines take the system out much faster. If you carefully add radial lines in incremental steps, you will start to hear the system fill in missing samples with an estimate, and then eventually fail to track.

Also fun stuff to do with audio fanatics:

After doing the marker test on one of their disks, point out that a good CD player will track right through a 2mm hole in the disk. Then palm their disk, preferably one of the gold plate flavor, sub one of your old junkers, and use a hand-held hole punch on the disk. It will fracture, and your audio fanatic passes out, or assaults you.

Tell them that the gold plating in "Ultradisks" is no better than aluminum, unless you intend it as jewelry. (Offer to do the scratch test to prove it.) That's why you are using a digital recording/playback system to begin with.

Explain Shannon's Sampling Theorm. Especially point out that exact reproduction requires infinite resolution of the sample, and you have only 16 bits. Suggest letters to the IEEE, Sony and Phillips demanding 32 or 64 bit a/d conversion, preferably at 1 MHz. Quote from one of the fringe magazines to support your claim.

Point out that having two d/a converters can be bad. That's because when you have two, the will (by definition) differ from one another. Announce that this makes for weird imaging effects in the upper registers. Mumble about "missing codes" and "differential nonlinearity." Then leave them listening intently to that CD of the maudlin jerk on the pan flutes. Remember to leave them water, or they sit there listening for a ghost in the machine for weeks, and eventually begin to smell.

If they won't listen for imaging problems, point out that with one d/a, you must have a sample and hold, which introduces a delay between channels of 11.5 microseconds. (There are plenty of ways to fix this, by the way, but it doesn't matter because...) Sound travels about 1250 feet/second (Students pay attention! I'm using mixed engineering units here!!) so in 11.5 usec it travels a little over 1/8 inch. So then go around and MOVE THEIR RIGHT SPEAKER! Ha ha ha...

Point out that a really, really good turntable costs much more than their CD player (or their car, for that matter), so it has to be better. You can get a reasonably insane turntable for about $5000, but if you skimp on the cartridge, you can get one for about $1000 more.

Also, point out that you own a Rumble King Turntable, Hummatron Amp with Total Harmonic Distortion (TM) (why settle for 0.25%, 1% or 3% when you can have the whole thing?), and Dynabuzz Speakers which cost only $98.99, and its _almost_ as good as your host's $7000 system. Fun-o. Remember to wear your approved face protection.

If taunting isn't your style, try sarcasm. Sarcasm is entirely lost on the truly fanatic. For example, suppose you are listening to an interminable monologue on the benefits of water cooled speaker cable. Try this: "Gee, I bet that water cooling really keeps the conductor temperature stable!" If you are really brave, ask about installation difficulties on your slab home.

I once purchased a coil of surplus copper strip. It was about 100 feet long, an inch wide, and about 0.073 inch thick. Whatever the exact thickness, I did some calculations, and determined that this strip corresponded to something around 11 gauge. My intent: to run two such strips, side by side, under a carpet for my speaker on the other side of the room.

Of course, a member of the Audiofile Youth caught me, and was delighted. "Is it for reduced cable inductance? Will it carry more than a kilowatt?" etc., etc. Uh, no, it just won't trip me as I change my Ultradisk recording of Disrali Gears.

Don't forget cleaning vinyl disks! Man o man, this can be hours of black (vinyl) magic. Tell them you use only detergents with lanolin in them, to lubricate the groves. Point out that the Nitty Gritty LP cleaner has a built in vaccuum cleaner, and uses special mystery cleaner. (BTW, I actually have one of these: it works pretty well, but is relatively noisy.)

If you are sufficiently versed in audio arcana, you never have to resort to rational arguments or (god forbid) engineering principles. And you may never have to listen to moronic claims about audio ever again. On the other hand, your victim might refer a fellow lunatic to your for information. Tough.

Next week: calculating skin effect at 20 KHz. And don't miss: the effects of annealing in OFHC on directional speaker wire.

For the record, I have some Harmon-Kardon stuff, and Rogers speakers. 8-)

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