Is it possible for VHS footage to erase itself?

[Sir_Loin]

Hi guys

Without it sounding like a stupid question, is it possible for the content of a VHS tape to be erased by time?

I have two separate clients who have given me two VHS tapes, which they swear have content on, yet when i play them in the two players that i have (Panasonic HS960 and a Toshiba player) both show no timecode on the clock and no vision. Almost like a blank tape.

They have not been near any large scale magnetic erasers either.

Am interested in hearing if its my two players or the tapes.

Thanks a lot

[solarfox]

...maybe?

Among other things, it depends on the storage conditions of the tapes; if they've spent years or decades lying around underneath a pile of junk in someone's garage, or in a non-climate-controlled storage unit exposed to temperature and humidity extremes, it's possible that they could have degraded, although I'd still be somewhat surprised if they self-erased completely... (Might also depend on the brand of tape, too; there was a lot of cheap low-quality crap being sold back in the day; some of it by fly-by-night outfits so cheap and dodgy that they didn't even bother to license the official VHS logo and just called their tapes "V-System" or some other thing.)

One thing I have run into, however, is that somewhere along the way several of the VHS manufacturers apparently dropped support for the 4-hour "LP" mode, and only supported 2-hour "SP" and 6-hour "SLP" (a.k.a "EP") modes. So if the tapes were recorded LP, and your players don't support that mode, then they won't play correctly (or at all).

S-VHS tapes wouldn't play in a VHS-only deck, but that Panasonic is an S-VHS deck, so that shouldn't be an issue...

Since you're in Australia -- are your clients sure that these tapes are PAL-format, and not NTSC? I'm pretty sure that Panasonic, at least, is not a multistandard player, so if you've got an NTSC tape on your hands and that's a PAL deck, that might explain it.

[JVRaines]

Without it sounding like a stupid question, is it possible for the content of a VHS tape to be erased by time?

Magnetic remanence does weaken very gradually with time, which results in reduced playback quality, but for tape to return to a completely random state ("erased") by natural processes would take longer than the time which has passed since JVC invented VHS. It's far more likely that the tape has undergone physical deterioration which renders the magnetic imprint difficult or impossible to read.

[KarMa]

I tried erasing VHS tapes with a powerful button magnet yesterday just by coincidence. It seemed to have little effect on the full spool inside the plastic case, and only seemed to erase when making direct contact with the exposed tape.

I use these same magnets for fulling erasing cassette tapes without opening the case. VHS seems to need a much more powerful magnet if you want to erase through the plastic and air gap.

[Cornucopia]

ALL magnetic media (audio/video/data, tapes, discs, etc) can lose their magnetism with time, but depending on the strength of the field, the pattern, and the retentivity this time can vary from a few years to over a hundred years.

Even simple medium-term storage has been known to allow magnetic fields to leak into surrounding segments, creating pre- and post-echo, in audio & video tapes. Which is why pro audio reels are always stored tails out (because post-echo is less objectionable than pre-echo). Video is less susceptable than audio (because of the helical scan vs. longitudinal). Digital is LESS affected than analog (because of regular sync pattern & EDC/ECC and signal regeneration), but not UNAFFECTED.

BTW, "button magnets" are NOT that powerful and they are of static polarity. Proper standard tape degaussers (the magnets that are actually meant to erase a tape) are 100s-1000s x more powerful, and they oscillate their charge to exercise & average the flux on the tape til it gets to near zero.
But you must remember, the influence of a magnet is inversely proportional to its distance. That's why the tape on the layer preceding/succeeding it is able to leak even though it's comparatively weak: it's only a few micrometers away.

But I would agree along with solarfox & JVRaines that there are more likely common-sensical causes to this playback problem.

Scott

[KarMa]

I would say that it's a LP play back problem, a signal that was recorded scrambled problem, or there's simple nothing on there. I have tapes that I can't play normally but can see the content or some semblance of content while fast forwarding (either damaged tapes or scrambled tapes).

Also heat is a major killer of magnetic media, but it probably won't completely erase it any time soon. Just drop the strength of the signal.

[hech54]

The entire tape from beginning to end with absolutely no shadows or any remnants at all of the previous recording?
Not a freakin' chance.

[JVRaines]

Print-through is usually not a problem with videotape because the signal is FM, not because of helical scan. The same way your car radio picks one FM station or another and never mixes them, only the stronger tape signal will be demodulated.

[hech54]

Print-through is usually not a problem with videotape because the signal is FM, not because of helical scan. The same way your car radio picks one FM station or another and never mixes them, only the stronger tape signal will be demodulated.

You are missing the point. Name a place in your home where you can place a VHS tape and come back a year later and it's completely devoid of any previously recorded video or audio throughout the entire tape.

[lingyi]

Open the tape cover (there's a little button on the side) and look at the bottom of the tape. That's where the control track is and if it's damaged (i.e. crinkled or torn), the video and HI-FI tracks won't work.

Have you tried checking if anything on the linear audio tracks (which are on the top edge of the tape, just to see if anything is recorded. This isn't affected by a damaged control track since it's read by audio only heads.

An LP (4 hour mode) recording is a possibility, but the majority of VHS VCRs will play back LP (some very early JVC models and professional models are SP only).

Another possibility is it's S-VHS trying to be played in a non-VHS VCR, though I think the time would still be shown.

PAL vs NTSC has been mentioned, though again, I think the time counter would still work.

As far as being accidently completely erased, that's highly unlikely. I have a home magnetic bulk eraser (for 1/4" reel to reel tapes) and as Cornucopia stated, it takes a LOT to completely erase a videotape. Full erasure requires several passes moving the eraser toward and away from the cassette. Commercial erasers can do it in a single pass, but they're way more powerful than my home model, And nothing you'd typically find in home or office environment has even as much power as my home unit.

That being said, a single pass with my bulk eraser on the bottom of the cassette (where the control track is) can cause playback issues, but not full erasure.

Hopefully Lordsmurf will post here to give more thoughts on the possibilities.