What's Up Wit' DAT?

Technology is not perfect. One aspect of technical perfection can be accomplished by balancing a healthy skepticism with a talent to extract the most
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Technology is not perfect. One aspect of technical perfection can be accomplished by balancing a healthy skepticism with a talent to extract the most

Technology is not perfect. One aspect of technical perfectioncan be accomplished by balancing a healthy skepticism with a talentto extract the most from your tools. Don't blindly assume allsystems are “go” simply because no obvious distortionis audible.

Products that inspire creativity and confidence do sowith a combination of functionality and their ability to delivermission-critical feedback warning of impending doom instead ofcrapping out at the most inappropriate time. This, however, assumeswe have been paying attention to the warning signs.


Digital technology has turned products that were formerly easyto “read,” such as tape recorders, into black boxes.Like the heading above, simple questions no longer have simpleanswers. This is especially true for the various digital cassetteformats. Once the cassette is loaded, problems are displayed ascryptic messages — made worse when using a numeric readout todisplay alpha-characters. We scurry to the manual to decipher errormessage codes, only to find that they have been poorly translatedfrom another language. For all of our efforts to do the rightthing, ending up with such a meaningless result is, as Orson Wellesonce described a voice-over session, “unrewarding.”


I recently read an article that included an interview with amastering engineer who, in my opinion, did a disservice to the DATformat by claiming that tapes become unplayable over time. I have acollection 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 intoconsideration that a poorly maintained machine can make tapes hardto play and that any machine can be adjusted to maximizeplayability. For helical scan digital audio recorders, the twoguides that wrap the tape around the heads are the equivalent ofthe height and azimuth adjustments for an analog recorder. Nomatter what format — DAT, DTRS or ADAT — some taperecorders are more tolerant than others to tape manufacturingvariations, because both mechanisms and head assemblies havetolerances as well, some of which (in my opinion) are too wide.


In the January 2001 “Tech's Files,” a basic blockdiagram detailed two test points — the RF Envelope and HeadSwitching signals — intended for oscilloscope connection tomonitor the signal from tape for calibration purposes. I recentlymodified a Panasonic SV-3700 for Michael Ryan at EMTEC (therecording media manufacturer formerly known as BASF), bringing thetest points out to the rear panel for quick and easy ’scopeaccess without popping the cover. There is no question if a tape isin or out of spec.

One side effect of this mod is that the ’scope connectionaffects error rate — no surprise, because technicians know touse “×10” probes to minimize the effect ofcapacitive loading on signal integrity. Using cables and not probeson the modified machine loaded the signal enough to increase errorrate, although the degree of data corruption inconsistently variedfrom tape to tape, proving that some tapes have more “dataheadroom” than others. This is more of a function of therecording process than the tape formulation.


Because tape is made in batches, there are variations to this“ironic” theme — hence, the recommendation thatnew tapes be fast-wound from end to end before use. Most of the“bad tape” I've encountered was sold under thenow-defunct DIC brand. As much as we'd like to blame the tape— and people have preferences — there are only a fewactual tape (and disc) manufacturers whose products are distributedunder several brand names.

Your bad experience may have been batch-related, but often atape recorder's condition is more to blame for the intolerance.Familiarity with head and tape path cleaning techniques, combinedwith the knowledge of electronic monitoring procedures, will makeyou and your machine less vulnerable to occasional clogs. In futurecolumns, I will be detailing machine-specific tips. Based on these,the astute reader can become less tolerant of problems and morelikely to send a machine out for service.


When tape and machine work together as one, you can't beat themfor tangibility. When the marriage fails, we often accuse the tapeof poor performance or worse, shedding. In reality, one tape playedin several machines will behave differently — some machinesare simply more capable than others are at extracting useable data.A “good” machine puts the strongest, most readablesignal on tape and, conversely, is capable of extractingthe most useable data from any tape. How do you know?Check the Error Rate for starters!

The same applies to all media. There will always beerrors — Sony refers to the ability to recover data andtolerate errors without sonic disturbances as“concealment,” the digital data equivalent to“headroom,” the difference between nominal operatinglevels and clipping.


Record a series of test tones to all tracks of an analog taperecorder, and each meter responds instantly (in most cases) with a“systems” report. In addition, the trained eyes, earsand fingers of a seasoned technician can evaluate mission-criticalareas of an open-reel machine and feel its pain without tools.Ballpark tension can be judged by hand. With a good light source,the tape path can be inspected for tape skew at each guide. (Beyondthis, tools are suggested!)

Evaluating a digital cassette re-corder is never easy. Sony'sPCM-1610 and -1630 formats took advantage of existing videorecorder technology — via ¾-inch U-Matic tape —but from this point forward, the professional user has beeninsulated from the media and the mechanism. From a pro standpoint,these machines should have kicked DAT into oblivion, yet the 4mmformat has proven to be a formidable contender, more reliable thanmany people give credit to — considering its size andaffordability. Remember that DAT is a trickled-up consumer productthat was severely compromised during its formative stages by thehyped-up RIAA. (And, yes, I have my own suggestions for Napster etal. Contact info for my two wonderful lawyers is available uponrequest.)


Ages ago (January 1986), this humble technician stepped aboardLe Mobile to play tape op for Joe Jackson's live album, BigWorld. The goal of the recording was to capture the liveperformance — of both the musicians and engineers MichaelFrondelli and Guy Charbonneau — to stereo while running24-track analog only as backup. The 2-channel digital recording wasmade via Sony's PCM-1610 converter/processor and two U-Matic rentaldecks.

After the show, a quick spot check confirmed a clean recording;a relief, until the tapes were swapped. Playback in the oppositemachines was not inspiring. Compatibility was fair with occasionaland inconsistent dropouts. The machines were black boxes to me. NowI understand that poor alignment was the reason for the erraticperformance.


It is not my intention to suggest that users go much furtherthan popping the cover and cleaning the heads. Head cleaning is nota panacea but just the first suggestion from customer support andyour local technician. You should know at least that much and havesome familiarity with what “normal” is. As described inJanuary and in more detail at www.tangible-technology.com, learningto access the Error Rate display is the very best preventivemedicine. As we come to rely more heavily on CD-Rs, I encourageusers to contact manufacturers, coercing them to include an ErrorRate display as part of the feature set.

If you are a geek in training, then let me recommend WIHAscrewdrivers, available from my friendly competitor Paul Plotnickat Pro Digital at www.prodigitalinc.com. You can't have enoughtools, and these are the best screwdrivers I've found yet.


Okay, enough about heads and tape. Let's look at some of theother problems that often plague digital cassette recorders. I amnot obsessed with changing pinch rollers unless they are reallyglazed, but the capstan shaft should be scrutinized carefully,especially on a DAT recorder where tolerances are critical. Seefigure on page 108 to see the dirt build-up on a capstan. Whilethey are not at all easy to clean, I've seen DAT capstans coated ina thick, black funk (except for a 4mm swath where the tapetravels). This muck can lift the pinch roller away from the capstanenough to alter the tape path — reverse-play is a challengefor every recorder, even on its best days.


In my first Mix column (April 2000), I trounced themyth that Sony and Panasonic machines are aligned to a differentstandard. Older Sony DAT recorders are more likely to make out spectapes, yet they are also more tolerant of the same. Panasonic deckshold their alignment better but are less tolerant of poorlyrecorded tapes.

Most Sony recorders have fewer moving parts, because separatereel motors simplify and replace numerous wear-item parts, such asclutches, gears or pulleys, that transfer motion from the capstanmotor to the reel tables. Pioneer and some Alps transports have theaforementioned wear-item parts, as does Panasonic, the DAT machinemost likely to jam.

While most DAT problems are mechanical, many Sony recorders, forexample, slowly fail from cold solder joints. (Some of the mosttechnologically advanced manufacturers use consumer-gradeconstruction techniques that compromise their most innovativedesigns.) Poor soldering can cause frustrating intermittence thatultimately enrages users to do damage to the more vulnerable“accessories,” such as the loading mechanism.

While the Sony PCM-R500 is a favorite in its price class, italso has the most vulnerable loading mechanism of all DAT deckssave for microportables. At the first sign of intermittentbehavior, it's best to repair “simple” problems beforemore serious damage is done. Have a professional closely inspectthe soldering at all connectors and power transistors.


Current tape-based systems that started life in the 16-bit worldhave been expanded to their limit — either more bits or moresamples but not both. Disc-based systems will permit higher samplerates and bit depths together, putting more emphasis on the qualityof interconnections, cables, transmitters and receivers —all the more reason to include data integrity indicationof the incoming signals, as well as the media, on all products.

As with error rate, knowing the “quality factor” ofthe arriving signal can either inspire confidence or initiate theinvestigation process. Better signal quality (from tape, disc orcable) improves the data recovery “headroom” andultimately the quality and consistency of the sound. With-out it,all the king's horses and all the king's men will not be able toreassemble a digitized Humpty Dumpty.

Eddie Ciletti can be reached at his Web site at www.tangible-technology.com.