Bulk Erasing Audio
And Digital Magnetic Tapes

(OR... Who Put The "Whomp" In The "Whomp, Whomp, Whomp"!)


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The Technique For Best Bulk Erasing
What To Get And Where To Get It



The "whomp, whomp, whomp", is a low frequency repetitive artifact left by improper technique in the erasing process! They sound like a low frequency "whooshing" noise or a "whomp" and can often be heard on improperly erased analog audio tapes (cassette and reel-to-reel), particularly when tapes are wound at high speed while listening to the audio output. Nobody seems to know what these "whomps" would translate to on data or digital audio tape, but you can be sure it is NOT to be welcomed by any equipment!

The "whomp's" are inadvertently recorded by using the wrong technique, while trying to erase the tape, usually by switching the eraser off while the tape is still in the eraser's magnetic field, or sharp jerky movements of the tape while erasing. Broadcasters discovered the benefits of carefully erasing cartridge tapes when it was found that very low frequency "whomps" were knocking their transmitters off the air! It follows, that the cleaner erase job you do, the less potential problems you will encounter later.

(Within this paper, I will be referring to a specific bulk eraser unit,
and I will give full details on it.)

For DATs, I do a rotary "wipe", three times (about 2 seconds total) on the top and bottom of the DAT shell... releasing the power switch each time I'm clear of the shell. Doing it that way, I can fully erase up to 20 DATs before the thermal switch cuts out, and the eraser has to cool before further use.

The whole trick is to move the tape slowly in and out of the eraser field. DO NOT switch the eraser off until the tape is well clear of the eraser and you don't feel any "tug" of the magnetic field on the tape. Remember, the eraser is plugged into the 60Hz power line, which means the magnetic field is doing the following, 60 times every second:

Starts at zero intensity,
Builds to maximum intensity,
Diminishes to zero intensity, reverses polarity,
Builds to maximum intensity,
Diminishes to zero intensity, reverses polarity,
 (and does the whole thing over again, and again, and again, and so-on...!)

Now, if you release the eraser power switch WHILE the field is covering the tape, AND the field is anywhere between zero and full intensity, you effectively record the magnetic field on the tape in the form of a "whump". That's what you hear when you play back an audio tape, and it's anybody's guess what a DAT or computer thinks (or does) when it is a data tape that has been "whumped"! (All this presumes that you successfully erased all remnants of the previous recording, otherwise that is also factored into the whole mess, "whumps" and all.)



  1. Rewind the tape fully so the tape pack is all at one end. This is a good practice to adopt, since most DAT tape damage occurs on loading or unloading the tape from the machine.

  2. Switch on the eraser, and bring the tape to the eraser.

  3. Rotate the tape or eraser over the region of the tape pack... there's no point to covering the whole plastic cassette since you are trying to erase the tape pack, not the plastic box it is loaded in!

  4. Three rotations (about 2 seconds total) on both sides of the cassette, over the tape pack, works for most applications. You will feel a strong "pull", on the cassette box, from the eraser's magnetic field as it is rotated over the area of the tape pack. You should be able to completely erase up to 20 DATs this way, before the thermal cut-out operates, and then the eraser must be allowed to cool before further use.

  5. If the cut-out operates WHILE you are erasing a tape, re-erase that one when the eraser has cooled, otherwise, it's "whump" time!

  6. Remove the cassette from the eraser to about a distance of one foot before switching the eraser off.

  7. Many people complain of strange problems with DAT tapes that run from unexplained muting to bursts of digital noise and odd clicks and pops. The blame is often laid at the feet of the "one pass" DAT tapes that are being offered by a variety of dealers, at very attractive prices. Other than price, there are some compelling reasons to use these tapes, and they are described elsewhere in detail.

    It is NOT the fault of the tape, but rather, the fact that the tapes were not properly bulk erased before using! The solution is a simple one...


    I adopted this procedure a long time ago, and it has served me well over more years than I care to remember.

    Recent tests have proved this over and over again... an un-erased tape that would not record properly, worked fine AFTER bulk erasing. Bulk erasing returns a tape to its original manufactured "blank" condition. If you have read manuals like SONY, Tascam and others, they say in essence...

    " Note that 'blank' tape that has never been recorded is different from 'blank' tape that has been recorded with silence - the latter is recorded with sub code information such as ABS and PROGRAM time information."

    Tapes that have been used for DATA purposes, (like the "one-pass" tapes) may have recorded information on them that "confuses" the DAT recorder when you try to record on them for audio purposes... the cure is to return the tape to the original un-recorded manufacturer "blank" condition by bulk erasing it.

    I bulk erase EVERY "one pass" DAT that I use, and I've gone through about a thousand over the past year, with NOT ONE PROBLEM. I spent a lot of time testing un-erased and erased DATs... no problems with the erased DATs, but a variety of problems cropped up with the un-erased DATs, from what appeared as drop outs (muting) to digital noise, tics and pops that weren't traceable to anything else. In one case, recording over the muted spot a number of times did nothing... inspecting the tape showed no physical defect... but after bulk erasing it, the problem could not be duplicated and the entire tape performed perfectly.

    If you want more information about "one pass" DAT tapes, see a separate paper describing their use and sources.


    The metal particle tapes, and that includes DAT, SVHS and 8mm video tapes, require far more magnetic force than any of the bulk erasers can deliver that were intended for brown oxide audio tapes.

    A serious problem is the choice of bulk erasers that are presently available to the average user... most types simply WON'T do the job with a DAT or a video tape because these metal based tapes need very high magnetic flux to properly erase them. Many of these bulk erasers just can't deliver the magnetic flux to do the job.

    I have tested the Radio Shack bulk eraser, catalog number 44-233, and found that it was really marginal for erasing DAT tapes... if you were not REALLY careful, and at least doubled the pass time for each side of the tape, it didn't do a complete erase job. I hesitate to think what a job it would do on VHS video tape with it's thick tape pack. I would ONLY recommend the Radio Shack eraser where NOTHING better is easily available AND, with the caution that you test it carefully before relying on it.


    Sorry, but you need a new bulk eraser... the old ones, at worst case, likely won't work and at best, they won't do a complete erasure, which often is worse than none at all, since it lulls you into a feeling of "having done something"!



    The only bulk eraser I know of that does a GOOD job is the Model PF-215 made by Geneva. It should sell for less than US $75, which sure beats the big ones for casual use, and it does work as described... Using the correct technique, up to 20 DAT tapes can be fully erased before the thermal safety cut-out kicks in, and I have to wait a while for it to cool down and reset before using again. Erasure is complete, even on VHS video tapes, when proper technique is observed.

    The specifications for the model PF-215 are:

    2800 Gauss flux field (more than enough to erase DAT and VHS metal tapes)
    Thermal breaker to prevent overheating
    Hand held
    Push button on/off power switch
    UL & CSA approved for safety.

    The unit is described as "the most powerful hand held eraser, 2800 gauss flux field", and is said to "deep erase type IV metal particle tape and DAT tape" as well as "all types of video tape including 8mm and S-VHS".

    The PF-215 is made by:

    Geneva Group of Companies, Inc.    (Correct as of 06/25/97)
    7109 31st. Avenue North
    Minneapolis, MN. 55427-2848
      Phone: (612) 546-5620
      FAX: (612) 546-0933

        1-800-358-5600 Toll Free

    They do not sell direct, but a call to the above toll free number should get you the name of the distributor/dealer, nearest to where you live, where you can see and/or buy their products. Get a few names and call around to get the best price:

    I bought mine from:

    DBL Distributing Inc
    14151 N. 76th Street, #200
    Scottsdale, Arizona 85260
    (602) 596-8636 or Toll free: 1-800-733-6766



    I have no relationship with Geneva or any audio dealers. The comments in this paper come from years of direct experience and testing. I have used one of the Geneva PF-215 bulk erasers on thousands of DATs and other magnetic tapes, over a year or so, with complete satisfaction and no "defective" DATs were encountered.




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