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  #1  
09-12-2022, 10:48 AM
vikinagy97 vikinagy97 is offline
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I know that on the Internet, there are a lot of examples of similar questions, on various sites, and the answer is (almost) always the following: It is impossible to recover.

However, on another forum, somebody writes that recovering a previous recording is not impossible if the newer one is weaker than the previous one. For example, if the old recording was a TV show, and the new one was made from a channel with no signal. I have some tapes with similar overtapings.

I know that the recovered recording will not be perfect, but it may be just recognisable. Still, it would be good to know what was on those tapes previously, or just whether there was anything or not.
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  #2  
09-12-2022, 11:04 AM
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Quote:
Originally Posted by vikinagy97 View Post
the answer is (almost) always the following: It is impossible to recover.
This is correct.

Quote:
However, on another forum, somebody writes that recovering a previous recording is not impossible if the
"somebody" is an idiot. Lots of those on the internet.

Unrecording/unerasing a tape is like unringing a bell, revering virginity, etc. Nope.

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newer one is weaker than the previous one.
Jabberwocky nonsense.

This person is conflating magnetic data recovery vs. audio-visual re-recordings. Not the same.

Read this: https://en.wikipedia.org/wiki/Data_remanence
NOTE: Wikipedia is, of course, NOT a 100% reliable source of info, as anybody can edit it. That said, it does act as a good primer/overview, in most cases. But the fine details may be wrong.

Audio-visual re-recording is essentially overwriting.

Quote:
and the new one was made from a channel with no signal.
It had visual data, even if that data was "snow" or nothing.

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I know that the recovered recording will not be perfect,
It won't be anything at all. Nothing will be "recovered".

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  #3  
09-12-2022, 04:01 PM
latreche34 latreche34 is offline
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It is 100% impossible for a very simple reason, the tape is completely erased when making a new recording using a head called full erase head, Even if the full erase head fails, the video heads do overwrite on the old recording whether there is a video being recorded or not resulting in a no RF signal.

Computer data recovery in the other hand is possible because when data is erased, It's only erased from the table of content, so the tape does not have to spin all the way to the contents to physically erase them, It just tells the system the space is available for recording, In this case it is possible to recover that data, but if the same section is used for a new recording there is no way in hell that it can be recovered.

It is the same scenario by the way for any type of memory storage, HDD's, flash media, optical rewritable media, SSD's ...etc.

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  #4  
10-04-2022, 07:09 AM
dpalomaki dpalomaki is offline
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It is possible in spy/crime fiction.

To add a couple thoughts: I agree that for all practical purposes it is impossible to recover useful video from an tape that has been recorded over. Some remanent of the prior recording might be present under limited conditions, but it would require what are often called "national means" to recover anything and then it would not be useful video or audio for anything but intelligence purposes.

For this to happen the machine used to over record would have to be misaligned compared to the original recording and/or the record field from the heads (both record and erase) would have to be weak. If the new recording was done in insert mode the full tape erase head would not be used so misaligned heads might leave a remanent of the old track signal between the head scans. A non-HiFi VCR might leave a remanent of a HiFI track. A stereo linear track insert recording might leave a remanent of an original mono linear track recording in the guard band space between the tracks. The content of the new video itself would have little if any effect on this.

Remember, they couldn't find the missing 18.5 minutes on the Watergate tapes.

One protocol for data data from discs call for many (is it 7?) actual overwrites of the disc space (sectors) that were used by the file being deleted.

The moral is after you record your baby's first steps enable erase protection (e.g., pop the protect tab) before you set the tape aside lest your significant other use the tape to time shift their favorite rom com. (Don't ask ho I know this! )
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  #5  
10-04-2022, 08:01 AM
vikinagy97 vikinagy97 is offline
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Quote:
Originally Posted by dpalomaki View Post
It is possible in spy/crime fiction.

For this to happen the machine used to over record would have to be misaligned compared to the original recording and/or the record field from the heads (both record and erase) would have to be weak. If the new recording was done in insert mode the full tape erase head would not be used so misaligned heads might leave a remanent of the old track signal between the head scans. A non-HiFi VCR might leave a remanent of a HiFI track. A stereo linear track insert recording might leave a remanent of an original mono linear track recording in the guard band space between the tracks. The content of the new video itself would have little if any effect on this.
Then it is not 100% impossible. I have also read that even if it is possible, it would be very expensive. I have many tapes on which one VCR recorded, then another, different one overwrote that. They could also be different in the feature you mentioned (Hi-Fi or not, ) and in the number of heads, for example.
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  #6  
10-04-2022, 08:20 AM
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Quote:
Originally Posted by vikinagy97 View Post
Then it is not 100% impossible. I have also read that even if it is possible, it would be very expensive. I have many tapes on which one VCR recorded, then another, different one overwrote that. They could also be different in the feature you mentioned (Hi-Fi or not, ) and in the number of heads, for example.
No, it's still 100% impossible. At best, what you can get is incomplete fragments. It won't be video content, but more like forensic evidence. Maybe, at best.

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  #7  
10-04-2022, 09:48 AM
dpalomaki dpalomaki is offline
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Very expensive - YES, very specialized gear and skill set needed.

Incomplete fragments at best - YES

Useful video for a consumer wanting to see their graduation procession or clearly hear the concert solo - NO

You might see snips of underlying video if there were gaps in the over-recording. (Enough to grab a few frames. This requires user error by the person recording over the original video.)

You might possibly see glimpses of individual fields if the over-recorder had a clogged head, not very likely.

Since you have the tapes, if the current (on top) video plays reasonably well, forget any chance of meaningful recovering what it was recorded over.

However, you are looking for evidence for a divorce case, crime, or similar purpose where something fragmentary and ugly is still of use, you could contact one of the 'spooky" companies that specialized in data/video recovery to price it out and get their assessment of the potential for recovery of watchable video.
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  #8  
10-04-2022, 09:52 AM
vikinagy97 vikinagy97 is offline
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I don't expect it to be a perfect video, either. Even those incomplete fragments would show whether there was any previous content or not on some of my tapes which weren't recorded by me but by others.
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  #9  
10-04-2022, 02:31 PM
dpalomaki dpalomaki is offline
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Your tapes, your time, your money.
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  #10  
10-04-2022, 09:11 PM
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Quote:
Originally Posted by vikinagy97 View Post
Even those incomplete fragments would show whether there was any previous content or not on some of my tapes which weren't recorded by me but by others.
I doubt you'd even get that.

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  #11  
10-05-2022, 02:37 AM
latreche34 latreche34 is offline
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Again, the full erase head is your problem, no matter how miss aligned the VCR is or HiFi or not HiFi, the full erase head will wipe out every magnetic particle found on the tape surface, hence 100% impossible.

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  #12  
10-05-2022, 06:04 AM
dpalomaki dpalomaki is offline
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Two things to keep in mind:
- the physical spacing of heads. The full erase heads comes before the spinning video/HiFI heads and the control/linear audio follows the spinning heads (this largely account for the glitch typically seen at the start/end of an over-recording)
- the full erase head does not operate in VCR with flying erase heads when recording in "insert" mode and the linear track may remain if "audio dub" is not active during the insert.

Depending on the machines involved and the user actions, these two factors can result in fragments/remanents of the original recording to remain on the tape. (Useless remanents for most purposes but they may give a hint as to the overwritten video at those points.)

But IMO the topic of this thread is not the general focus of this board and the OP might do well to explore forums focused on forensic analysis of video tape rather than capture and restoration of otherwise readable analog video.

Also, video storage on analog tape is very different from digital data stored on media such as disk drives, memory cards, etc. To over simplify with analog video when you record over (erase the original recording) you effectively "burn the library" and to recover you are left sorting ashes to see if there are any remanents you can read. On the other hand with digital data on a hard disk or memory card you typically just "burn the card catalogue" unless you or the OS go to pains to also remove it from the shelves.

Reminder to would be malefactors: always stir the ashes after you burn the letter, never leave the phone note behind pad after writing on it., and destroy the typewriter ribbon and platen after typing the incriminating note.
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  #13  
10-05-2022, 10:26 AM
latreche34 latreche34 is offline
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I don't think that's what the OP is asking for, From his original post he is talking about TV shows and stuff, So linear audio alone or the 2" section from the video heads to the full erase head is no concern to him.

https://www.youtube.com/user/latoak34/videos
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  #14  
10-05-2022, 10:32 AM
vikinagy97 vikinagy97 is offline
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What/who is that OP?
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  #15  
10-05-2022, 10:53 AM
dpalomaki dpalomaki is offline
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OP = original poster

On the other hand post #1 & #8 imply he would at least like to know whether or not there was something taped over, even if not recoverable

All in all an interesting discussion of what might and might not be possible as opposed to what can/should be done to with working recordings.
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