1088 Chapter 28
hard disk drives are cheap enough to just store the hard
drive as the archival copy. This strategy is fraught with
problems that could come back to bite the user. Disk
drives have several failure mechanisms that can render
the data unrecoverable over time.
Some systems park the head on the surface of the
disk. Over time, the lubricant that is embedded in the
disk’s coating can migrate to the surface and “glue” the
head to the disk. This problem is avoided with drives
that have parking ramps to hold the heads off the
surface of the disk when the disk drive isn’t running.
Another problem is the spindle bearings. If the drive
is stored for extended periods, the lubricant may
degrade or migrate away from the critical bearing
surfaces. This can lead to bearing failure when the drive
is restarted.
The manufacturer rates a typical drive for about
three years of useful life. There is no separate specifica-
tion regarding storage life. Expecting a long storage life
is an act of sheer faith.
The advantage of a tape or optical disk backup of the
digital data is that the media and the mechanism are two
separate items. The drive mechanism can be maintained
and serviced without involving the media. The problem
then becomes finding a working sample of the appro-
priate drive, or finding parts and a trained technician to
fix a nonworking sample. Several digital tape formats
have already reached the point at which finding a
working tape deck to play the tapes is difficult or impos-
sible. This problem will only get worse in the future.
If the data is valuable, the user should map out a
backup strategy that will assure accessibility. This may
require occasional copying of the digital information to
newer formats. If nothing else, the user should have a
schedule to verify every year or two that the original
data can still be accessed without any degradation.
28.5.11 Data Interchange
Standards for compatibility of digitally recorded tapes
have become much more difficult to achieve because of
the wide range of choices open to the digital audio
designer. The common problems of mechanical compat-
ibility of tape speed and track format are still present,
plus the sampling rate, data format, timing, and
error-handling methods must also be compatible.
The rapid evolution of digital audio technology in
these areas, which has already rendered several genera-
tions of digital audio recorders obsolete, has blunted
any attempts at standardization at the media level. The
point of data compatibility has moved up to the elec-
tronic interface between systems. At this level we find
widely used standard protocols such as AES/EBU,
SPDIF, and ADAT light pipe. Additional work, such as
AES 31, to standardize file transfer protocols between
hard disk systems will provide for the electronic trans-
port of audio files throughout a facility via local area
networks, and throughout the world via the Internet.28.6 Tape Recorder Transport, Maintenance, and
TestingMaintenance begins with inspection and cleaning.
Before starting the cleaning procedure, note the location
and type of dirt and debris that has accumulated due to
prior use. Excessive debris indicates that your recording
tape is being slowly destroyed by the tape transport.
A deposit of very fine, silky threads indicates that
the polyester base film of the tape is being scraped off
by a sharp edge on a guide flange. Examine all edge
guides for grooves cut into the flanges by the tape.
Either reposition the guide to place an unworn surface
in contact with the tape or install a new guide if the
groove is severe.
Deposits of brown or black dust near the guides indi-
cate that the edges of the tape are being scraped or
deformed enough to break small chunks of coating from
the edge of the tape. Check the tape tension and the
height of the guides and reel hubs.
Any caked-on deposits on the surface of the guides
or heads are very serious. Inspect the surface of the tape
for scratch marks. If the tape surface is being scratched,
continued use will destroy the tape. Correct the cause of
the scratches before continuing.
Several types of cleaners are available for cleaning
tape machines. Older head cleaners usually contained
Xylol, a strong solvent, to aggressively dissolve tape
residue. Milder isopropyl alcohol is a more popular
solvent today, but avoid rubbing alcohol containing
30% water in favor of the 99% pure variety for topical
antimicrobial use.
Use a soft swab moistened with cleaner to scrub the
contact surfaces of the heads, guides, and capstans.
Avoid drenching the swab. If the swab is too wet,
solvent may run down the capstan shaft into the top
bearing, washing away the bearing’s lubrication. Cotton
swabs are suitable for most analog tape recorders but
not for the delicate heads on a helical scan recorder. Use
special lint-free swabs with more pliable sticks for
cleaning rotary head machines.
When cleaning the head, always rub the swab in the
direction of tape motion, never across the head side-
ways. Sideways scrubbing may peel away the edge
laminations of the cores. Avoid scraping the face of the