Bulk-erasing tapes--MacDV Digest #1796

[Ted Langdell]

Erica's right about "a lot of art and science" being involved.

The science is matching the amount of magnetic force it will take to erase a
specific type of tape with a bulk eraser which will completely do the job.

The bulk erasers that Radio Shack may sell are probably fine for audio tapes
up to 1/4" in width, but beyond that you need to look for a professional
model.  

That's because compared to audio tape, modern videotapes (and other data
media) require a much higher level of magnetic force‹coercivity‹to change
their polarity during recording.  That force is measured in oersteds.  To
erase a tape requires even more force that during recording.

The "art" is in being able to make sure that the entire reel or cassette has
been SMOOTHLY, uniformly and completely erased, so that there are no
portions of the tape which have "spikes."

If you listened to an audio tape that's been poorly erased, some of the old
recording may still "come through" or you may hear "whumping" noises caused
by un-even erasure.

On video, you'd see parts of a picture come through, or see varying
patterns/hear whumping in the audio track.

Those can sometimes remain after the tape has been recorded on after erasure
because the recorder might not have been able to completely over-ride the
poor bulk-erasure.

To get an idea of what kinds of erasers (and oersted levels) are needed for
specific media, try this link:

 http://www.garner-products.com/deg-guide.htm

to the Garner division of Audiolab Electronics, a Sacramento area company
which has been making degaussers (bulk tape erasers) for around 40 years,
now.

I've used a number of Audiolab erasers over the years, and they work well,
when used as directed for the media they were designed to erase.

Hope this is helpful.

Ted.



> From: "Macintosh Digital Video List" <MacDV at lists.themacintoshguy.com>
> Date: Fri, 13 Dec 2002 05:13:49 -0800
> To: "Macintosh Digital Video List" <MacDV at lists.themacintoshguy.com>
> Subject: MacDV Digest #1796
> 
> 
> Date: Thu, 12 Dec 2002 22:17:11 -0700
> Message-Id: <v04210103ba1f1d9353ae@[10.0.0.2]>
> From: "Erica Sadun" <erica at mindspring.com>
> Subject: [MacDV] Re: Erasing DV Tapes
> 
> At 7:17 PM -0500 12/12/02, Doug Mitchell wrote:
>> Does anyone know of a device which will allow me to erase may
>> digital video tapes.  I have about ten MiniDV tapes and I would like
>> to wipe them clean.
> 
> Bulk erasers will do this. I know Radio Shack carries
> them, and probably other places too. There's a lot of
> art and science involved. (Which model, how not to burn
> the house down, maximum time involved, safety precautions,
> etc). Google first, buy second.
> 
> -- Erica
>