Ok heres a question seems someone on the patriots was caught taping when he didnt have permission and offered several times to erase the tape and walk away … of course the security for the other team didnt take the deal
Now my question assuming he was actually using recording tape even if he erased it couldn’t a forensic av guy figure out to put it back together?
I know if its on a hard drive a pc tech guy can find things in a formatted hard drive that was supposed ot be erased …
Depends on the quality of the tape, and how much you’re willing to spend, but you can recover a lot of information from an erased video tape. Erasing things on disk often means just marking them “erased”, not actually overwriting the bits, so recovery is much easier.
Note: I will be addressing strictly the “tape” only side of things, regardless whether this is at all relevant to the circumstances that brought the question to the OP’s mind.
With classic analog magnetic audio tape, sometimes you can get lucky and recover a crappy version of what was erased. But it doesn’t always work. A famous case is the 18 1/2 gap on one of Nixon’s White House tapes. Despite extensive efforts, nothing was recovered outside of some information about the large number of erasures that erased the “accidentally” erased segment.
But that was a crappy Dictaphone type device. A different grade device might have different properties.
Digital magnetic tape (such as can be found on later generations of video recording equipment), has the same problem as a hard drive in erasing not being complete. The exact position of the heads over the helical tracks on the tape are even less likely to line up perfectly each time. Note that there can be a separate erase head that does a sloppy job.
One problem with recovery of digital audio is that goofing up several of the bits per sample datum is really bad. No way can that byte be accurately recovered. With analog, quite a few mistakes can still produce a understandable recording.
(Note that digitally encoded audio is typically stored differently from digitally encoded data on various media. E.g., with audio CDs, the error recovery bits are part of the data stream while for data CDs those are written in a separate field. This makes perfectly ripping an audio CD with problems like scratches harder than just copying a slightly iffy data CD.)
Also, if talking about classic VHS type tapes and such, the analog audio track is also recorded along with the digital one. So that gives someone “twice” the chance to recover something.
Of course, way too many people use terms like “tape” to describe things that aren’t remotely on tape.
thanks, i thought the “its gone forever” statement was as full of crap as my cat boxes are
Classic VHS tapes recorded in analogue only; there was no digital track. (There were some later VHS-style formats that were digital, though these never really took off.)
You certainly can’t reliably recover erased data. If you could, then they’d be using that technology to make storage media with twice the capacity.
Correct. VHS Hi-Fi was analog audio depth multiplexed under the video signal and required additional heads to record the audio signal before the video signal https://en.wikipedia.org/wiki/VHS. On the other hand, Beta Hi-Fi was analog audio that was multiplexed within the video recording spectrum and didn’t require separate heads: https://en.wikipedia.org/wiki/Betamax
There was a digital PCM adapter PCM-F1 introduced with the SL-2000 portable recorder that could record digital audio. The PCM-F1 was also compatible with some pro and high end consumer VCRs.
As ftg stated, on analog tape, in general once it’s recorded over, the original info is gone. However there are exceptions. Some professional reel to reel recorders had the ability to do sound on sound which was accomplished by lowering the strength of the recording heads on the second pass so the original track would “bleed through” and both signals could be heard. This can also happen in video recording if the erase head (which is supposed to fully erased the full width of the tape as it passes) isn’t working properly. Finally, it’s sometimes possible to recover part of the video signal if the original recording was done by wide video heads, as used for SP recording and the new video is recorded with the narrower EP/SLP heads since which doesn’t cover the full recorded width of the original tracks.
One other possibility. Because the full erase head is located several inches away from the video drum with the video recording heads, there can be a few seconds of unerased video visible when using resusing a previously recorded tape. This is because when you rewind the tape, there’s always a foot or so that remains on the ‘empty reel’, unlike when it came the factory. Even if you manually rewind the tape so none is left on the take up reel, because of the loading, you’ll never be able to fully erase that portion without using a bulk eraser.
Ancient tech 101: First, tape recording media is basically very tiny bits of magnetic iron suspended in a gel-type plastic emulsion deposited on a film of plastic. You record by passing the tape across an electromagnet, more specifically a “U” or more accurately, “C” shaped magnet; the gap between the two prongs of the “C” is the “Gap” and the most intense magnetic field. Anything over the gap is magnetized in the same direction as the field, the stronger the power to the magnet, the stronger the field, the more of the suspended iron particles that are polarized in the same direction as the magnetic field.
Audio (or a carrier signal modulated with TV video) is a wave, alternating between positive and negative of various frequencies and intensities. If the gap is small enough and the tape goes past it fast enough, the iron particles pick up this pattern of alternating magnetic fields. It can be read back with a similar electromagnet arrangement, but instead of powering the “head” it gets a magnetic field induced based on the magnetized tape passing over the gap.
To erase, write a solid magnetization one way or an alternating signal to re-align the particles as the tape goes by, or simply record something else so the particles are arranged differently. Now - maybe the signal did not completely erase the recorded signal, and there’s a residual “ghost” signal underneath from a portion of the particles not re-aligned. This is alleged possible, but note the Nixon recordings analysis failed to find this. Also, as the tape goes by the head, it may not perfectly line up; So think of the head writing as like a brush painting a line on the tape. You paint a new line, same width of brush - if it’s off by a bit or the tape wanders back and forth, you would see along an edge the remainder of previous recordings. This is why hard disk complete-wipe programs write random patterns, over and over (IIRC one standard was 35 times). If the tape head alignment is way off, there will be residual signal on the side. OTOH, the decent quality recording devices would be specifically designed to erase and overwrite so that you don’t hear “ghost” signals - after all the point of the hardware is to record*** only*** what the person is currently recording.
But despite wipe programs or tape erase/overwrite, I have yet to hear of a solid case where a recording was recovered after a real erase; but then, I haven’t been looking for it. Theoretically it can happen.
Most analog tape machines reel to reel, cassette, VCRs, etc. have a full erase head that erases the full width of the tape before it reaches the recording head(s). As shown here: https://www.oldtechnology.net/insidethevcr.html the full erase head is in the path before the video drum and the recording heads on a VCR. Exceptions are multitrack reel to reel audio machines: https://museumofmagneticsoundrecording.org/ManufacturersMultiTrack.html with an erase head could erase select tracks or the flying erase heads on high end and professional VCRs which were on the same spinning drum as the recording heads and could erase individual video tracks for editing and the full erase head is turned off.
The statement that: “Also, as the tape goes by the head, it may not perfectly line up; So think of the head writing as like a brush painting a line on the tape. You paint a new line, same width of brush - if it’s off by a bit or the tape wanders back and forth, you would see along an edge the remainder of previous recordings.” is correct in that this is one of the reasons why playing back a videotape on a different machine often results in less than optimal playback. In the case of a recording made on a machine with severely misaligned video heads, you may have to purposely misalign the video heads on playback machine to match. However, as I stated above, in normal operation, the full erase head completely erases any trace of the previously recorded video tracks.
Thinking about it. While I’m sure I’ve read about some video signal being able to be retrieved if the new video recording was done my a narrower head, barring the full erase head being disabled or severely malfunctioning there shouldn’t be any residual video information left by the previous recording.
That said, it may just be confirmation bias, but I swear a recording on a bulk erased videotape looked better than one erased by the head in the VCR.