Saying "No" to Death
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SOUND CHECK

Figure-1: A composite image showing the keystrokes to access the Block Error Rate (bEr) similar on both the DA-38 and the DA-78HR. Errors are indicated on the bargraph display. In the middle is the signal from tape monitored via oscilloscope. The dots above indicate errors (click image).

Checking the Error Rate is the best preventive maintenance because it clearly indicates the amount of data headroom available. Figure-1 is a composite of three images. At the top, three buttons are labeled 1, 2 and 3. Press SHIFT, then MENU, repeating MENU until "maintain" appears. Then press SUBMENU until "bEr" appears using the up/down buttons to select "on."

The Block Error Rate (bEr) is displayed using the LED meters - A-head on 1, 3, 5 and 7, B-head on 2, 4, 6 and 8. The meters are only accurate when the machine is in playback mode. From Stop to Playback, the meters will peak, then settle. No lit LEDs means plenty of Data Headroom - an occasional flicker could indicate tape dropouts. The example shown in lower half of Figure-1 shows three LEDs consistently lit indicating that something is compromising performance, though not enough to illuminate the PB Condition LED.

Note: The PB Condition LED is ON when bEr-on is displayed and the SHIFT LED is illuminated. Press SHIFT and the machine stays in bEr mode, the eight bargraphs display tape errors and the PB condition LED toggles on and off. When bEr is off, the PB Condition LED should be off 99.99% of the time. A major dropout might flash the LED, but it is mostly there to tell you when it's too late.

The middle of Figure-1 also features a "geek insert," a view of the RF envelope (the signal from tape) on top of which are error flags derived from pin-2 of TP-1509. The errors are from the same tape that consistently lit the LEDs below. Anyone familiar with the RF envelope will know that this one looks quite good, yet something is wrong that will eventually cause a problem. If you are non-technical and stop reading now, just know that any lit LED segments (when in bEr mode) are a sign you should stop. Do not attempt an overdub. Clean the heads, clone the tape and check error rate again.

FISH STORY
There are two ways to tackle the mystery tape issue, user and geek. Users should try any of the available DTRS tapes - new stock only - knowing that all of them have a similar characteristic. I tried a brand new BASF / EMTEC DA-30 MP on the DA-78HR in 24-bit mode with perfectly fine results.

Figure-2: The "eye" pattern is observed by oscilloscope using the highest sweep setting, 0.1uS/div, in this case. The "eyes" are the dark spots created by the combination of 3.15mHz and 6.3mHz modulated signals. "Equalization" adjustments optimize the eye pattern and minimize the error rate
(click image for larger view).

The short story is this: Tape is made from rust, glue and plastic each with potentially variable properties. Tape heads are remarkably complex devices that are also subject to manufacturing tolerances. If "optimum" is the middle of the specification, a tape that is left of center and a machine that is right of center could trigger the error LEDs.

WARNING: Readers who blush at geek-speak may skip the next section, but check out the last paragraphs starting at "Moral of Story."

EYE-EYE, CAP'N!
Geeks and the curious should take a closer at the RF signals in Figure-2. Set the horizontal sweep as far as it will go - at least .1uS/div - and trigger on the incoming signal at TP3 and TP4. (This test does not require an external trigger.) The difference between the 16-bit and 24-bit eye patterns clear demonstrates the amount of additional information being squeezed on to the tape.

(The "eyes" are the dark spots.) The "brighter low-frequency" is 3.15mHz, recorded when Formatting. The data in the "background" is 6.3mHz. Adjusting the playback EQ - R53/54 for MP, R51/52 for ME tape - should enhance the eye pattern, the 3.15mHz signal should also be "square" and not tilted.

BIGGER is BETTER
From right to left (my Jewish ancestry by way of Calabria), Figure-3 shows the progression of increased signal - to and from tape - from the birth of DTRS through the present. Each vertical division represents 500mV. My ancient Tascam Test Tape, MTT-88101, is on Sony stock. Notice how its envelope (at right) falls below 1000mV. The DTRS stock in the middle, recorded on the DA-78HR, "kisses" the window, while the FUJI stock (also recorded on the DA-78HR) exceeds 1000mV in a healthy way.

Figure-3: From right to left, the output level of the signal from tape increases as improvements have been made to the DTRS heads and their electronics plus a little help from tape formulation tweaks (click image for larger view).

Increased output level is one way to improve data headroom. A clear "eye" pattern is another, relying on the quality fo the head gap plus a little EQ. The answer to the mystery tape question was a batch of Sony DARS-113MP. It wasn't new stock and it must have been just a little harder to erase than the EMTEC stock. I experimented with record current, the adjustments being at near maximum. Turning them full up just about made the LEDs go away completely. Then I tried FUJI stock, turning the record current down to simulate the reading of the mystery tape. The FUJI tape requires less record current even when blasting away previously recorded material.

MORAL OF STORY
Check error rate before a session. It's the only way to weed out potential problems -machine or media - especially those caused by tolerance issues. Mass production lives and dies by its ability to stay within tolerance - that's what ISO-9000 certification is about, though you don't often see it touted in our industry. For all machines that have dual-resolution capability, a problem in high-res mode may not exist in standard mode. Proving this is another way of confirming the available data headroom.

Many people ask me if it's OK to recycle tape. For both digital and analog, the ability to reuse tape is based on the machine's record and erase current, respectively, combined with head efficiency. Panasonic DAT recorders are most vulnerable, especially those made after 1994 (or if the heads have been replaced). Try recording over previously recorded material comparing a Sony DAT against a Maxell DAT checking error rate before and after. It might convince you to keep buying new tape.

Eddie would like to thank the following "enablers:" Phil Sanchez at Tascam for use of the machine, Jean Tardibuono and Natalie Stocker at EMTEC for their tape stock and John Calder of Heartland Marketing for the FUJI tape stock. PS: By the time you read this Eddie will have become a papa for the second time.

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