Conference back40::soapbox

    Some digital format comments:

    DAT: sampling rate: 32, 44.1 and 48kHz. Not all units support
                        all sample rates.
         tape format:   4 mm, cassette

         run  time:     up to 2 hours

         copy prot:     required on "consumer decks", easily defeated
                        or not installed on "professional decks"; one
                        digital copy allowed, but a bit is set in the
                        data stream disabling multiple generations
                        (digital copies of copies). Uses a mechanism
                        called "Serial Copy Management System" (SCMS),
                        which was endorsed by the RIAA after their
                        mechanism was rejected (which involved making
                        a "hole" in the frequency response that would
                        get progressively worse in each generation.)

         compression:	None

         main
         manufacturer:  Sony for consumer apps; the Panasonic DA3700 is
                        the most popular deck currently in use in
                        recording studios and professional apps.

    DCC: sampling rate: fixed 44.1
         tape format:   standard cassette, modified to utilize high-
                        density metal-particle tape; with appropriate
                        "knock-outs" added to the case to indicate
                        format type.

         run time:	90 minutes

         copy prot:     none

         compression:   Lossy. See description of algorithm below.

         main
         manufacturer:  Philips; most common consumer product is
                        by Marantz. Format has largely been a bust,
                        even though suitably equipped recorders
                        can also play standard audio cassettes.

    MD:  sampling rate: fixed 44.1

         run time:      60 minutes

         copy prot:     none

         compression:   Lossy.

         main
         manufacturer:  Sony; Minidisk player recorder available
                        in "Walkman" sized unit. Has not made a
                        big splash in the consumer market, and has
                        no presence in professional applications.


    Lossy compression (used by both MD and DCC) analyses the
    frequency content of the signal. This produces a two
    dimensional array of frequency and amplitude. Below a
    certain amplitude threshold, the frequency information
    is considered insignificant. This information is discarded
    from the table. Using Huffman encoding, the table is
    then further reduced. The player reproduces the input
    signal by decoding and expanding the table.

    A panel of "Golden Ears" was assembled by Studio Sound
    magazine (a professional audio engineering magazine
    published in the UK). The panel concluded that MD and
    DCC were inadequate for all professional applications.
    The consumer response has not been much better.

    However, the same compression techniques are being applied
    to the MPEG and MPEG II standards and many movie titles
    with digital soundtracks (with lossy compression) are
    likely to be available on the CD-ROM format in the near
    future.

    -b

    Oops... forgot some information in -1. If there's an advantage
    to MD, it's that the media is "random access" (like a CD).
    No waiting for tape for forward or rewind to access points.
    The media format of MD is similar to a 3.5" floppy, but
    slightly thicker.

    Also, one of the advantages of DCC is that there's a lot
    of "user bits" on the media, which can be used to do some
    very nice indexing... like putting the title of the track
    in each track, etc.

    -b

    So, the copy guard stuff lets you copy things once? After that you
    can't?

    Re .3
    
    Correct.  Units containing the copy-protection circuitry will refuse to
    copy a tape that has the "I'm a copy" bit set.

    What if you are recording something from a CD?

    SCMS applies _only_ to digital copies. Some consumer DAT products won't
    allow you to make digital copies at all... of course you're always
    welcome to make as many "analog" copies as you want.

    On the consumer decks that do support digital copying, but also
    have SCMS, the input from the CD player would have the SCMS
    bit clear, so you can make a copy of the CD. However, the
    DAT deck will write the SCMS bit as it stores the data to tape,
    disallowing you from making a 2nd generation digital copy of
    the tape. First generation copies are always OK.

    On "professional" DAT decks, the SCMS bit is neither checked
    or generated.

    On my "semi-pro" DAT deck (a Tascam DA30), there is a jumper
    on the circuit board which you cut to disable SCMS... and
    Tascam frequently includes the instructions for doing this
    operation in their newsletter... but because anyone can walk
    in off the street and buy a DA30, they have to leave the SCMS
    intact by default.

    -b

    Just another random comment about tape formats:

    DAT, like VCRs, use helical scan, i.e. moving heads. This
    allows for greater data capacity without compression, but
    with some reduction in mechanical reliability.

    DCC, on the other hand, uses the standard "fixed head" in
    a cassette, although there are more "tracks" and the tape
    only moves in one direction.

    BTW - I would like to correct an earlier statement; since
    the tape can only move in one direction, I believe the
    longest DCC run time is 45 minutes (unless they allow
    use of 120 minute tapes which are discouraged in regular
    cassette mechanisms).

    -b

>    DAT, like VCRs, use helical scan, i.e. moving heads. This
>    allows for greater data capacity without compression, but
>    with some reduction in mechanical reliability.


Would it be possible to briefly describe how this works without
getting too technical? I.E. how does "helical scan, i.e. moving heads"
allow for greater data capacity on a linear tape? Is it like the
data is in a short frequency sine wave with lots of skinny blips
on the tape? (I don't know how well I described what I was thinking
of but it is a serious question.)

    Jack,
    
    The head is a cylinder that rotates at approximately 45 degrees
    to the tape path, at fairly high speed. Think of a cross-section
    of tape; the head "spins" over this area, writing side-ways.
    
    -b

Does that mean that the data path looks like -

----------------------------------------------------
\ \-\
 \ \ \  etc. in a "serpentine" fashion so that at any
  \_\ \_     linear point along the tape, "N"
-----------------------------------------------------
    ^
    N

there can be more than one bit of data?

    Yes, Jack that's it. 
    
    \ \
     \ \ 
      \ \
       \ \

    Another big advantage of that format is that the speed relative to the
    tape of the record/playback head(s) is far higher because of the
    resultant speed of tape transport vector-added to helically-scanned
    head(s).  This allows for far higher frequencies to be recorded by a
    given head gap.  I learned most of what I know about tape-recording
    technologies during the Watergate Tape analysis...
    

    .10, .11
    
    Not quite serpentine fashion, Jack.  Your piccie shows the track going
    downward, then along, then back upward.  It doesn't do that - all scans
    are downward.  The gap scans once across the tape, then spins across an
    empty time when it's being whirled arount to line it up for the next
    pass.  The angle of scan is a lot shallower than 45 degrees - it's more
    like aobut 15 degrees.  The mechanism pulls a loop of tape out of the
    cassette and inserts the head assembly into that loop; the oxide is
    therefore on the inside of the tape, not on the outside as it is with
    ortdinary cassettes.  With the loop, there's a very short time when the
    gap is not in contact with the tape.
    
    -dick

    DVD is coming soon! (I hope)

    just picked up a new one for the new kitchen...had to shell out few
    extra bucks at the "Country Furniture Store for a stand the wif wanted
    to go with the new kitchen...BTW, this prolly belongs in the tth, but
    since we got our new kitchen, the wif has been cookin up a storm and i
    prolly put on 5 lbs in the past month...can't keep up w/the leftovers

    A new one what?

    a new piece of home entertainment hardware...whcha thunk

    Oh, well, I don't want to hear about your sex life.
    
    

    
    Oh, home entertainment hardware.  I've seen those at Spencer's Gifts
    and in the back of {cough} magazines.
    
    And you got one for your wife?  Hmm.
    
    Brave of you to share that with us, Ronnie.
    

    looky, hindskits, I was talking about new telly, not whachubeen
    receiving in the brown unmarked wrappings  :-0

    now Miss Deb is jumpin' in on top of me...I was talkin 'bout a lousy
    telly

    
    I never 8^o!
    
    

    besides, what kind of stand can u get at the country furniture store
    for the stuff u guys r talkin' about

    
    A hands-free facial massager!  What a concept.
    
    

    i dare to ask...what sizes do they come in?

    Hands free for what?

    I dunno, Skits, but I like the entertainment part...

It gets so bawdy in here during the evening ....

    Thanks for joing this strange pahrty, Jack

    Just read about a new subwoofer being put out by Sunfire (ala Mr.
    Carver).  Supposed to be "flat to below 18Hz" and can "reproduce any
    frequency between 18Hz and 120Hz at 110dB SPL in a typical listening
    room".  According to the reporter who listened to it as CES: "He's not
    kidding.  The killer bass track we auditioned left us looking for 
    a hiden monster module - which didn't exist."
    
    It's called the True Subwoofer.  It is only an 11" cube, which used 2-
    7- inch drivers in a push-pull configuration.  It is powered with a
    servo-controlled 2700 (!...possibly a typo??) watt amplifier.  It has a
    36dB- per octave low pass that can be set anywhere from 40 to 120Hz.
    
    Price?  $1,095.  I may have just found the perfect subwoofer for my
    system, should it sound half as good as it specs out.  Now, all I need
    is a house to put it in.  8^)
    
    
    [This topic has been dormant for a while, so I thought I'd enter
    something...this is one of my favorite subjects, after all.  8^)]

> Now, all I need is a house to put it in.  8^)

And, if that wasn't a typo, I hope the house is next to your very own
hydroelectric plant.

Now, can you help Mz_Debra with her speaker problem?

    
    Yeah 8^(!
    
    

    Okay Mz_Debra...the stereo doctor is in.  Please give me the details...

    
    
    I wonder of stereo-geeks wear socks with their sandals..?
    

    Say again?

    
    
    I wonder of stereo-geeks wear socks with their sandals..?
    

    stereo geeks always wear jeans, a t-shirt (faded) and jogging shoes,
    although they never jog.

    .34
    
    Not this one.  I am a stereo geek AND a master of fashion.
    
    
    .37
    
    I also jog/run.  
    
    
    8^)

    There are always anomalies. But Steve, you know what I'm talking about.
    Besides, if you were a real stereo geek, you wouldn't be working for
    Digital.

    
    	Sounds like a nice sub, Steve.
    
    	Push-pull ... that's a face-to-face Isobarik set-up, right?
    
    	I had built a pair of mid/low-bass push-push Isobarik boxes for
    	my GTI [for about $160 total, using RS 8" poly drivers] but they
    	were stolen out of the car.  I was not happy.
    

    .40
    
    I can relate to the car gear getting ripped off...yes, I can. 
    That's why I now drive a junker (with no stereo) and am working on my
    HOME theater/stereo setup.  
    
    Getting ripped off twice is enough for me...
    
    
    re: push-pull set up
    
    Actually, it isn't a face-to-face isobarik set-up.   The picture shows
    the speaker cone facing outward.  It is likely a set-up with one woofer
    mounted on both the front and back, facing outward, wired out of
    phase. This is not the only possibility, but given the size of the
    cabinet, it makes the most sense.
    
    
    -steve

Steve,

I fully expect you to be called on the carpet in WM about this 
extravagant purchase next time you reply to the welfare note...

daryll

    8^)