MiniDV tapes and Magnetism at DVinfo.net

Steven Taylor · September 12th, 2007, 04:58 AM

My spouse accidentally left one of my MiniDV HDV Tapes on top of one of my studio audio monitors last night...

The tape seems to play fine on quick inspection.

What is the danger with MiniDV tapes and electromagnetic fields? Is there any real data out there or just hearsay?

Mike Teutsch · September 12th, 2007, 05:27 AM

Steven,

I think you are pretty safe. Old VCR tapes and others were vulnerable but the new MiniDV tapes are almost invulnerable! I have tried and others here have posted stories about trying to bulk erase tapes with very heavy magnets. None of us have had any luck. I tried with a big magnet I have and I could not even get a drop. I believe there is a post by Chris Hurd in this forum about why they are so difficult to erase.

Good Luck---Mike

Mike Teutsch · September 12th, 2007, 05:36 AM

Here's an excerpt from a Glenn Chan post:

miniDV tape uses metal evaporated (technology). It has much higher coercivity than metal particle (i.e. VHS), which makes it much harder to erase.

Mike

Steven Taylor · September 12th, 2007, 05:37 AM

Ah that's good news, as I seem to live and work in caves of massive electromagnetism :)

Steven Davis · September 12th, 2007, 06:18 AM

Ok, I'll throw my wrench in. I had a similar question regarding storing hard drives and dv tapes in a safedeposit box. So I called one of the techys at Maxell, since Maxell is the brand I use. The first time I called, the dude told me that there shouldn't be an issue since most hard drives have sheilding. Well that wasn't exactly a 'no.' So when I got closer to setting up my storage, I called again. I got a different dude, and he told me that I should in no certain terms store my hard drives with dv tapes as prolonged exposure would affect the tapes.

So who knows, I just wanted to throw out there what the Maxell dude told me.

Chris Medico · September 12th, 2007, 06:55 AM

Something to consider here is the difference between a static and a dynamic magnetic field and the overall strength of the field.

A static field like with a speaker that isn't being used won't affect the tapes in the short term mostly due to the relatively weak field and the fact that its static. Since the field is static the areas of highest affect would happen along a magnetic force line which would not erase the tape but just make a dropout. A moving magnetic field would sweep force lines across the tape and could erase it. This would take a long time unless the field was VERY strong.

The magnets in a hard drive are MUCH stronger than in most speakers and you can place the tape closer to them. Its not the magnet that records the data onto the disk (that is an electromagnet) but the magnet that is used to move the heads back and forth across the disk that is the problem. On a side note, if you ever want to make a fridge magnet that would hold about anything, take apart an old hard drive and get the magnets out.. Watch your fingers, they will pinch you good when they snap onto the fridge. Your kids latest masterpiece will be safe from blowing off I assure you! ;)

Still the risk is very low if there is a few inches of space between the drive and tapes since the field strength drops quickly with a small distance. Also a tape wound on a spool is MUCH harder to erase than a single strip of tape held into open space.

In short, if you can get the tapes a few inches away from a hard drive the risk is minimal. For most speakers, the cabinet itself will move you far enough away from the magnet to not be a problem there either.

Chris

Steven Davis · September 12th, 2007, 06:59 AM

Good info Chris, thanks.

Mike Teutsch · September 12th, 2007, 07:17 AM

Steven,

You point a major problem with getting answers to questions in this entire industry. Questions about cameras, tapes and many other things are just not answered or are answered by people who really don't know, listen to urban legends or just guess.

Think of all of the questions we are constantly asking about MiniDV tapes and simply can't get definitive answers, even from the manufacturers. Wet vs dry, etc.. Getting answers to camera problems is no better. After years of us saying that the Canon auto lenses couldn't focus and zoom at the same time, because they have only one motor, we just found that that information was totally incorrect! In all of those years, Canon never stepped up and gave us the answer. I'd even bet that they were called or written about the problem too. And, I'm a proud owner of two Canon cameras and have owned three others.

As a breath of fresh air, we do have CineForm! They have been great about answering questions and being honest about quick to respond to any problems.

Contrast that with Focus Enhancements. Most questions are not answered. I recently sold my FS-4 to a guy in Texas. He called Focus Enhancements before buying it from me on ebay. He specifically asked the representative if it would work with his JVC HD camera and the guy told him, "Yes!" Well, they will not. He called back after receiving the unit and not having it work and a different rep said, "No it will not work with it!" He was upset and I don't and didn't blame him. He asked if I would give him a refund and I told him yes, but he would have to reimburse me for my costs, shipping and fees etc.. He decided just to resell it. Put him several weeks behind in getting the correct unit for his camera and cost him a lot of extra money. All of this because a rep gave him the wrong answer to what was a very simple question.

OK, rant off, but how about all of you company reps out there trolling these threads give us some info. You don't have to give out trade secrets!!!! :)

Good news, your tape is likely not harmed. Bad news, you can't readily erase your tapes. :)

Mike

Jim Andrada · September 12th, 2007, 07:41 PM

To paraphrase an old song "Nobody knows...."

I'm totally non-surprised by this. After 50 years in the computer biz I've come to accept it as normal.

Let's face it - tech support guys and salespeople are not usually engineers. The real engineers are few in number and very busy developing new products. And even if the tech support guys get the engineers involved (which they should at some point) the technical complexity of today's products just about insures that no single engineer knows about the whole product.

The motor specialists do the motors, the firmware guys wrtie the code, the electronics guys do the cards, etc etc etc. The motor guy has little idea what will happen when some other group decides that they need to accelerate the motor faster than the original designer had thought about, the firmware guys aren't prepared for some of the more interesting side effects that happen under various stress conditions. Heck, even finding out what component is at the root of the problem is painful.

And even worse, no company I know of these days does the whole job. Everybody buys chips and circuits and miscellaneous components from other vendors, who buy from another layer of vendors, etc and there are always little "surprises" lurking as every application seems to unearth new problems that the vendors never thought of.

I was involved in a mammoth example of all this when one of our OEM customers started seeing failures in a motor that involved a buildup of material on the motor brushes. We had never seen this kind of problem in several hundred thousand units, but since the motor was failing we all ganged up on the motor maker. Teams of people converged and went through every process in the motor assembly line that we could think of as a source of contamination. We even did chemical analyses of the line workers' cosmetics!

It all led nowhere. In the end it turned out that a completely different part on a card installed by our customer was outgassing and the part was in proximity to the motor and it just so happened that the particular compund being outgassed would form a hard crud in the presence of an electrical arc - for example the little spark you'd get when a motor brush passed across the gap between conducrors in the commutator. The motor maker had no idea that their motor would be used in an environment where this gas was present, the engineers who spec'd the motors had no idea that the customer would install a card with this kind of component on it etc etc etc.

I think between all the companies involved we spent over a million dollars tracking this thing down.

I've been focusing on field problems, but the same dynamic is at work when a user asks what they think is a simple question about how a product will perform for a given application.

Nobody knows... Try it and see what happens.

Glenn Chan · September 12th, 2007, 10:14 PM

with a normal tape eraser, I can't manage to erase a miniDV tape. With enough effort I can get a rolling bar of dropouts on the tape. So I would say that the tape is likely good.

2- If the 1s and 0s are being read back properly, you'll get a perfect digital copy. The tape implements error correction, so a few 1s and 0s read back incorrectly will get corrected (and "hidden"). If there are too many errors, you see dropouts.

3- You can make a backup of your tape if you are worried about it.

September 12th, 2007, 04:58 AM	#1
Steven Taylor Regular Crew Join Date: Jul 2007 Location: London, UK Posts: 44	MiniDV tapes and Magnetism My spouse accidentally left one of my MiniDV HDV Tapes on top of one of my studio audio monitors last night... The tape seems to play fine on quick inspection. What is the danger with MiniDV tapes and electromagnetic fields? Is there any real data out there or just hearsay?

September 12th, 2007, 05:27 AM	#2
Mike Teutsch Inner Circle Join Date: Oct 2004 Location: Port St. Lucie, Florida Posts: 2,614	Steven, I think you are pretty safe. Old VCR tapes and others were vulnerable but the new MiniDV tapes are almost invulnerable! I have tried and others here have posted stories about trying to bulk erase tapes with very heavy magnets. None of us have had any luck. I tried with a big magnet I have and I could not even get a drop. I believe there is a post by Chris Hurd in this forum about why they are so difficult to erase. Good Luck---Mike __________________ Chapter one, line one. The BH.

September 12th, 2007, 05:36 AM	#3
Mike Teutsch Inner Circle Join Date: Oct 2004 Location: Port St. Lucie, Florida Posts: 2,614	Here's an excerpt from a Glenn Chan post: miniDV tape uses metal evaporated (technology). It has much higher coercivity than metal particle (i.e. VHS), which makes it much harder to erase. Mike __________________ Chapter one, line one. The BH.

September 12th, 2007, 06:18 AM	#5
Steven Davis Inner Circle Join Date: Jun 2004 Location: Richmond, VA Posts: 3,065	Ok, I'll throw my wrench in. I had a similar question regarding storing hard drives and dv tapes in a safedeposit box. So I called one of the techys at Maxell, since Maxell is the brand I use. The first time I called, the dude told me that there shouldn't be an issue since most hard drives have sheilding. Well that wasn't exactly a 'no.' So when I got closer to setting up my storage, I called again. I got a different dude, and he told me that I should in no certain terms store my hard drives with dv tapes as prolonged exposure would affect the tapes. So who knows, I just wanted to throw out there what the Maxell dude told me. __________________ What happens if I push the 'Red' button?

September 12th, 2007, 06:55 AM	#6
Chris Medico Inner Circle Join Date: Aug 2006 Location: Efland NC, USA Posts: 2,322	Something to consider here is the difference between a static and a dynamic magnetic field and the overall strength of the field. A static field like with a speaker that isn't being used won't affect the tapes in the short term mostly due to the relatively weak field and the fact that its static. Since the field is static the areas of highest affect would happen along a magnetic force line which would not erase the tape but just make a dropout. A moving magnetic field would sweep force lines across the tape and could erase it. This would take a long time unless the field was VERY strong. The magnets in a hard drive are MUCH stronger than in most speakers and you can place the tape closer to them. Its not the magnet that records the data onto the disk (that is an electromagnet) but the magnet that is used to move the heads back and forth across the disk that is the problem. On a side note, if you ever want to make a fridge magnet that would hold about anything, take apart an old hard drive and get the magnets out.. Watch your fingers, they will pinch you good when they snap onto the fridge. Your kids latest masterpiece will be safe from blowing off I assure you! ;) Still the risk is very low if there is a few inches of space between the drive and tapes since the field strength drops quickly with a small distance. Also a tape wound on a spool is MUCH harder to erase than a single strip of tape held into open space. In short, if you can get the tapes a few inches away from a hard drive the risk is minimal. For most speakers, the cabinet itself will move you far enough away from the magnet to not be a problem there either. Chris __________________ http://www.LandYachtMedia.com

September 12th, 2007, 05:37 AM	#4
Steven Taylor Regular Crew Join Date: Jul 2007 Location: London, UK Posts: 44	Ah that's good news, as I seem to live and work in caves of massive electromagnetism :)

September 12th, 2007, 06:59 AM	#7
Steven Davis Inner Circle Join Date: Jun 2004 Location: Richmond, VA Posts: 3,065	Good info Chris, thanks. __________________ What happens if I push the 'Red' button?

September 12th, 2007, 07:17 AM	#8
Mike Teutsch Inner Circle Join Date: Oct 2004 Location: Port St. Lucie, Florida Posts: 2,614	Steven, You point a major problem with getting answers to questions in this entire industry. Questions about cameras, tapes and many other things are just not answered or are answered by people who really don't know, listen to urban legends or just guess. Think of all of the questions we are constantly asking about MiniDV tapes and simply can't get definitive answers, even from the manufacturers. Wet vs dry, etc.. Getting answers to camera problems is no better. After years of us saying that the Canon auto lenses couldn't focus and zoom at the same time, because they have only one motor, we just found that that information was totally incorrect! In all of those years, Canon never stepped up and gave us the answer. I'd even bet that they were called or written about the problem too. And, I'm a proud owner of two Canon cameras and have owned three others. As a breath of fresh air, we do have CineForm! They have been great about answering questions and being honest about quick to respond to any problems. Contrast that with Focus Enhancements. Most questions are not answered. I recently sold my FS-4 to a guy in Texas. He called Focus Enhancements before buying it from me on ebay. He specifically asked the representative if it would work with his JVC HD camera and the guy told him, "Yes!" Well, they will not. He called back after receiving the unit and not having it work and a different rep said, "No it will not work with it!" He was upset and I don't and didn't blame him. He asked if I would give him a refund and I told him yes, but he would have to reimburse me for my costs, shipping and fees etc.. He decided just to resell it. Put him several weeks behind in getting the correct unit for his camera and cost him a lot of extra money. All of this because a rep gave him the wrong answer to what was a very simple question. OK, rant off, but how about all of you company reps out there trolling these threads give us some info. You don't have to give out trade secrets!!!! :) Good news, your tape is likely not harmed. Bad news, you can't readily erase your tapes. :) Mike __________________ Chapter one, line one. The BH.

September 12th, 2007, 07:41 PM	#9
Jim Andrada Inner Circle Join Date: Feb 2007 Location: Tucson AZ Posts: 2,211	To paraphrase an old song "Nobody knows...." I'm totally non-surprised by this. After 50 years in the computer biz I've come to accept it as normal. Let's face it - tech support guys and salespeople are not usually engineers. The real engineers are few in number and very busy developing new products. And even if the tech support guys get the engineers involved (which they should at some point) the technical complexity of today's products just about insures that no single engineer knows about the whole product. The motor specialists do the motors, the firmware guys wrtie the code, the electronics guys do the cards, etc etc etc. The motor guy has little idea what will happen when some other group decides that they need to accelerate the motor faster than the original designer had thought about, the firmware guys aren't prepared for some of the more interesting side effects that happen under various stress conditions. Heck, even finding out what component is at the root of the problem is painful. And even worse, no company I know of these days does the whole job. Everybody buys chips and circuits and miscellaneous components from other vendors, who buy from another layer of vendors, etc and there are always little "surprises" lurking as every application seems to unearth new problems that the vendors never thought of. I was involved in a mammoth example of all this when one of our OEM customers started seeing failures in a motor that involved a buildup of material on the motor brushes. We had never seen this kind of problem in several hundred thousand units, but since the motor was failing we all ganged up on the motor maker. Teams of people converged and went through every process in the motor assembly line that we could think of as a source of contamination. We even did chemical analyses of the line workers' cosmetics! It all led nowhere. In the end it turned out that a completely different part on a card installed by our customer was outgassing and the part was in proximity to the motor and it just so happened that the particular compund being outgassed would form a hard crud in the presence of an electrical arc - for example the little spark you'd get when a motor brush passed across the gap between conducrors in the commutator. The motor maker had no idea that their motor would be used in an environment where this gas was present, the engineers who spec'd the motors had no idea that the customer would install a card with this kind of component on it etc etc etc. I think between all the companies involved we spent over a million dollars tracking this thing down. I've been focusing on field problems, but the same dynamic is at work when a user asks what they think is a simple question about how a product will perform for a given application. Nobody knows... Try it and see what happens.

September 12th, 2007, 10:14 PM	#10
Glenn Chan Inner Circle Join Date: Jun 2003 Location: Toronto, Canada Posts: 4,750	with a normal tape eraser, I can't manage to erase a miniDV tape. With enough effort I can get a rolling bar of dropouts on the tape. So I would say that the tape is likely good. 2- If the 1s and 0s are being read back properly, you'll get a perfect digital copy. The tape implements error correction, so a few 1s and 0s read back incorrectly will get corrected (and "hidden"). If there are too many errors, you see dropouts. 3- You can make a backup of your tape if you are worried about it.