Archiving LPs on Video Tape

["ROSSI J.A." <rossi@nusc.ARPA>]

Just a word of caution to people who intend to use video tape as a medium
for archival storage of music from LPs, CDs or elsewhere.  Although the
comments I am about to make concern Beta- and VHS- HIFI, they are almost
certainly valid for 8 mm as well.  

The two 1/2" formats (Beta and VHS HIFI) utilize what is really an analog
method of storing sound on tape.  The process AFM involves modulation of a
carrier frequency which is located within the video bandwidth of the
recording process.  Although the manufacturers claims that the method is
rouhgly equivalent to recording in a convethional recorder at over 200 ips 
(most analog stuff is recorded at 32 ips), the claim is somewhat misleading.
It is true, however, that both formats allow the recording of audio signals
infinately better than any currently available cassette recorder and at least
on a par with most high end consumer and 'quasi-pro' reel equipment (i.e., 
the subtle differences between true pro mastering equipment and the video 
formats is not important here).  What is important is not the 'sonic-attributes'but the physical attributes of the media.

Consider a reasonably affordable, high quality, 'quasi-pro' (Tascam, Otari,
Revox, etc) mastering deck.  It will usually use 1/2 in audio tape (1.5 m
with backcoating), run at 15 ips and record in two tracks (each a little
more than 3/16" wide) in te same direction.  With some normalally used noise
reduction system (eg. Pro-DBX) its electronic specs will exhibit frequency
responses of about 30-22000 Hz, about 90-100 dB of dynamic headroom and
no appriciable wow and flutter.  VHS-HIFI (for example, Beta specs are slightly
better) claims 20-20000 Hz frequency response, 80 dB headroom, and no measurablewow and flutter.  Both have a noise ceiling well above 70 dB (basically 
inaudible at normal listening volumes).  On paper (and on hearing) the two
formats are close enough to be called equal.  What is severely different,
is the most fundamental point, THE TAPE itself.

Whereas, 1.5 mil backcoated mastering audio tape is nearly invunerable to
anything save temperature extremes and fungus, video tape (even the highest
grade super extra high quality, dyna-super-beridoxi-epitaxica-HIFI tape) is
a frail beast, initially subject to dropouts, and with a not too highly
regarded longevity (i.e., when archival considerations for video storage
film vs tape were argued several years ago, the theorists put a 10 year max
shelf life limit on videotape (1/2 ") even when stored at ideal climatic
conditions.).  Another severe problem with video tape is its most limiting
characteristic 'splicing-impossibility (i.e., if audio tape recorded at
15 ips breaks, a half inch can easily be removed for a splice and the effect
on the musical program (figure a 1/30 sec loss) will, under most circum-
stances be un-audible. Consider, 1/30 of a sec is a video frame.  Now 
consider how many consecutive video frames are stored in a 1/2 in of tape
(I actually dont know but figure the heads revolve at about 300 ips and the
strike that, its 300 rpm, and the tape moves at less than 1 ips, giving a
balpark figure of about 5 frames or 5/30 sec loss [best case], or at
least 5 times the loss of the audio tape.  Couple this with the synch
problem not shared by audio tape and the results of a broken tape could be
disasterous).  Back to the first problem, as video tape ages its paerticle
bonders degrade making it more subject to dropouts.  As video, the dropouts
are seen as momentary noise bars across the screen, in hi fi, the sound
like they look (imagine a schscschschsshchch in the middle of one of the
Fairlight glisandos in Mother Stands for Comfort, for example).

In conclusion, the video tape solution to audio needs is important.  I have
replaced my trusty old Revox A77 with a JVC VHS HI-FI video recorder.  For
final archival purposes, however, I dub back to my Tascam 8 channel deck
using 4 tracks for each stereo channel.  Therefore, while video tape HIFI
makes a real nifty substitution for a mastering deck for mixdown purposes
(i.e., for some purposes its even preferable to reel decks), it is no
substitution for the longevity and non-degraded archive results you can
expect from audio tape when properly stored.

Now, talking about something I have no experience with, 8 mm tape.  I would
think that the problems I cite above with the 1/2 in formats would be
severly compounded with 8 mm.  First the tape is much thinner (i.e., less
bonders) and obviously moves much slower (size is time and shorter lengths
need to move muchh slower to get equivalent playback times), therefore, I
would suspect that dropouts are probably at leat as frequent and ther tape
is much more brittle than 1/2" tape.  Second, the method of audio in the
8 mm format is digital PCM (Pulse Code Modulation), similar to that used
by CD players however utilizing only one half the word size (i.e., CDs use
a 16 bit PCM word whereas the converters in 8 mm are only 8 bits wide).  This
alone has tremendous implications for dynamic tracking of input signals, and
has resulted in a less than acceptable frequency response (30-15000 Hz).
Therefore, all other things being equal, the 8 mm format starts out at a
sonic inferiority to the analog methiods used in the 1/2 in video formats.
Couple that with the concept of digital dropout (this is a much more severe
problem than analofg dropout because it can effect any parameter of the sound,
and not simply be interpreted as a momentary gush of noise or non existence
of sound (have you ever heard a CD mistrack ot dropout, not a pleasant
auditory experience).

In summary, if you think you want to listen to your recordings ten years
from now, or you think you would like to have your grandchildern appreciate
Kate, Peter and the like, keep your records or better yet buy CDs or analog
laser disks.  The two later possibilities give you all the sound you need
and are nearly indestructable.  If you must use tape, buy a high quality
1/2 track 1/4 in deck amd use it at 7 1/2 ips (slightly less frequency
resp, but better overall characteristics than 8 mm video tape)


In long winded apology,

John
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