Up Wit' DAT?
Common Failures of Digital Tape Machines
by Eddie Ciletti
Products that inspire creativity and confidence do so with a combination of functionality and their ability to deliver mission-critical feedback warning of impending doom instead of crapping out at the most inappropriate time. This, however, assumes we have been paying attention to the warning signs.
ARE THE REELS TURNING?
Digital technology has turned products that were formerly easy to read, such as tape recorders, into black boxes. Like the heading above, simple questions no longer have simple answers. This is especially true for the various digital cassette formats. Once the cassette is loaded, problems are displayed as cryptic messagesmade worse when using a numeric readout to display alpha-characters. We scurry to the manual to decipher error message codes, only to find that they have been poorly translated from another language. For all of our efforts to do the right thing, ending up with such a meaningless result is, as Orson Welles once described a voice-over session, unrewarding.
I recently read an article that included an interview with a mastering engineer who, in my opinion, did a disservice to the DAT format by claiming that tapes become unplayable over time. I have a collection of music DATs used for post-surgery recorder evaluation. Some are nearly 10 years old and still playable.
To make such an uninformed statement does not take into consideration that a poorly maintained machine can make tapes hard to play and that any machine can be adjusted to maximize playability. For helical scan digital audio recorders, the two guides that wrap the tape around the heads are the equivalent of the height and azimuth adjustments for an analog recorder. No matter what formatDAT, DTRS or ADATsome tape recorders are more tolerant than others to tape manufacturing variations, because both mechanisms and head assemblies have tolerances as well, some of which (in my opinion) are too wide.
FKA: FORMERLY KNOWN AS
In the January 2001 Techs Files, a basic block diagram detailed two test pointsthe RF Envelope and Head Switching signalsintended for oscilloscope connection to monitor the signal from tape for calibration purposes. I recently modified a Panasonic SV-3700 for Michael Ryan at EMTEC (the recording media manufacturer formerly known as BASF), bringing the test points out to the rear panel for quick and easy scope access without popping the cover. There is no question if a tape is in or out of spec.
One side effect of this mod is that the scope connection affects error rateno surprise, because technicians know to use x10 probes to minimize the effect of capacitive loading on signal integrity. Using cables and not probes on the modified machine loaded the signal enough to increase error rate, although the degree of data corruption inconsistently varied from tape to tape, proving that some tapes have more data headroom than others. This is more of a function of the recording process than the tape formulation.
Reprinted with permission from Magazine, March, 2001
© 2000, Intertec Publishing, A Primedia Company All Rights Reserved
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