Conference cookie::notes$archive:cd_v1

592.0. "** DAT - specs and test info... ***" by 50580::REIF (Fire (KA) and Water (SUI)) Thu Jan 08 1987 04:51

************  I'd like to open a new note on
    		- specs on DAT
    		- testing info on DAT
    		- Q/A on above
    
    Understanding DAT, plse refer to note 451 first !!!
************
    
    
    
    Latest news on DAT from good ol' europe
( extract from magazine "digital audio 1/2 1987" )

re. 451.7
........... DAT will not be able to seek to any track more or less
instantaneously....


re. 451.10
............DAT is serial access (hence no instant track seek).....



	Please see following specs !!!!


It might be not the best english (for the article is in german), but I
hope I get the contents right!!!



Digital Audio Tape
==================

The digital challenge


The digital Audio Tape (DAT) starts in Japan probably this year (1987)
in spring and in europe (germany) next autumn.
In Japan the same time it hits a competition: 
    the re-writable MAGNETO OPTICAL DISC  (MOD)     see also note #451
						    for more details !!

So the enduser gets two alternative systems to record with. They both
got the advantages of digital technics, like 
	o  dynamic range
	o  permanent storage (regardless of age)            *** !?
	o  error correction
	o  comfortable usage,
but the DAT were given the better chances.
It has a longer recording time, which is good for background music,
and based on the handling it's better for usage in a walkman and in
car stereo. The compact form of the cassette is the biggest advantage.

...... DAT-recorder, that you could easily carry, would be interesting
to record Live-atmosphere of a concert, etc.
The domain of MOD will be in the area of communication systems and
computer peripherals.
The latest introduced DAT recorders (on fairs !!) are very nice to look
at and you can hardly see the difference to CD-players. New with these 
recorders are the recording level instruments, the displays and the 
switches to set the subcodes.
Interesting on the technical side is the seek (access) time, that's
quicker than with CD, and the error correction, that's much better due
to the higher error rate of the software.
The DAT will soon get it's part in the home stereo equipment; even more
because there's a video system, based on the same cassette, projected for
the future ! 


Technical Specs:
================

Cassette size				73x10,5x54 mm
form					closed unit
magnetic tape width			3,8 mm
magnetic tape thickness			0,0013 mm
recording time (stand. tape)		2 hours

head					RDAT (rotary)
head diameter				30 mm
absolute speed of tape			8,15 mm/sec
drum rotation				3000 rpm
relative tape/head speed		13,3 m/sec		***!!!

access time				max. 1 sec
rewinding time				10 sec.

block sequence				8 sync bits, 8 Id bits,
					8 block addr., 8 parity bits,
					8 subcodes, 5 AFT,
					128 blocks with each 288 PCM bits
reading					top down

program seek				up to 200 times the speed
features				programming,
					repeat of sequence/title/cassette,
					next/prev. title, intro scan
reconstruct of data			in buffer
buffer					2 x 64 Kbit
sampling frequencies			44,1 / 48 / 32 KHz



Thats all uncommented data (except ***!!) and I have more if someone
wants !!!
If someone knows where to put this data also, plse tell me !!

Some testing info on a "Luxman DAT KD-117" will follow !
    
    
    best regards
    
    Manfred Reif, IIS-Unit Frankfurt Germany
    
    
P.S.:  I'm a digital fan for years now; I got my CD player in
       the summer of 1983 (a Phillips CD 202) and I'm still
       happy with it - now I also got my Sony Discman for Car !
    

    Re: .0
    
>    access time				max. 1 sec
>    rewinding time				10 sec.


    The DAT can 'access' any selection on the tape in < 1 sec. ??!~?!?
    Or does 'access time' mean something else here ??  Also, does rewind
    time of 10 sec. mean the whole tape can be rewound in 10 sec
    (incredible) !?!  Does the DAT use the same tape are 8mm video (if
    not, how is it diffrent?) ??
    
    -mike
    

    Re: .1
    
    According to .0, the tape is only 3.8 mm wide, considerably smaller
    than 8mm video.  The mention of video must be a completely new
    standard. (Just what we need, we've already got three)
    According to the speed and time, the tapes are over 60 meters long,
    so a winding speed of 6 m/s is quite fast, but perhaps possible.
    Seems to me that access time must mean something other than 'time
    to find any track', even if the winding time is 10 sec.
    
    -Steve
    

    
    re: "time to find a track" v "access time"
    
    whether they're the same thing or not, I don't know, but as an example
    of the time taken to find a track, a DAT player was demo'd on the
    BBC program "Tomorrow's World" last week, and it took 5 sec from
    track to track (admittedly the guy only selected two, but it gives
    ya some idea anyways).  In true BBC (i.e. non-commercial TV) style,
    the name of the player was blanked out, but I could make a good
    guess that it was a SONY.  
    
                                      Ian!
    

	Isn't DAT set up similar to the "audio-only" system that 8 MM
	video uses?  If I recall correctly, 8 MM uses 8 or so digital
	tracks "in parallel" on the tape, and each is good for lets say,
	2 hours of sound.  then tracks can be 'accessed' much faster than
	actual tape rewind, simular to old 8-track tapes.

	???

    No, DAT is not similar to the "audio-only" system of 8mm video.
    Well, it's similar only insofar as they're both digital PCM-encoded
    audio.  8mm video uses 8 bit sampling, at a frequency of something
    like 35K Hz.  DAT uses 16 bit sampling at 48K Hz.

If "access time" meant what it does on a disk, then a 1 sec access
and a 10 sec rewind is not consistent.  Just "access" the first
selection instead of rewind.

Since this is rotary-head DAT, I suggest that "access" here means
the time to load the tape around the drum.  1 sec sounds reasonable
for that operation, considering the size of the drum and tape, and
the fact that it has to be done gently.

The 10 sec rewind would be done with the drum unloaded, just as in
a VCR.

    Re:.5  Just a point of clarification.  I understand that prerecorded
    DAT's will be sampled at 44.1khz like CD's.  The playback unit will
    be capable of the 32, 44 and 48khz playback to accomodate whatever
    was used in the recording.  The 48khz rate was designed to preclude
    digital copies in the home and is only used in the record/playback
    mode in the home players.