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Q: Need HELP recovering recorded-over clip from MiniDV tape!!! ( No Answer,   7 Comments )
Subject: Need HELP recovering recorded-over clip from MiniDV tape!!!
Category: Science > Technology
Asked by: subirs-ga
List Price: $2.00
Posted: 04 Jun 2004 11:47 PDT
Expires: 04 Jul 2004 11:47 PDT
Question ID: 356478
My question is very simple. I am asking if the following is possible,
if so, could you list a few professional recovery sources in the USA
(preferably Richmond, Virginia or in Phoenix, Arizona)??

I have a Sony TRV-20 MiniDV camcorder. I accidentally recorded over an
important clip. Is it possible to recover the recorded-over clip?

I DO NOT reuse tapes. So this clip has been recorded over just once
and played 3-4 times.

Please let me know if you require further clarification.

Thank you.

Camcorder: Sony TRV-20
Tape Format: Mini DV
Recording Format: SP (Short Play)
Record date: 2001
There is no answer at this time.

Subject: Re: Need HELP recovering recorded-over clip from MiniDV tape!!!
From: netcrazy-ga on 04 Jun 2004 12:45 PDT
Hello subirs-ga,
Sorry to hear about this.

I don't think it is possible to recover this recorded-over clip. I own
a camcorder having a mini-DV and once my wife accidently recorded over
another video, I was not able to recover that video at all.

Subject: Re: Need HELP recovering recorded-over clip from MiniDV tape!!!
From: funkywizard-ga on 05 Jun 2004 13:52 PDT
There are two answers to this question. Basically the cheap answer and
the expensive answer. I guarantee you that the FBI or a similarly
sophisticated recovery service could recover the data, but at a high
price and not with certainty. If the data is worth at least hundreds
of $ to you, then it could be possible. If it is not possible or you
are not willing to pay hundreds of dollars to have someone
professionally reconstruct the video, then no, it cannot be recovered
by any easy or inexpensive means.
Subject: Re: Need HELP recovering recorded-over clip from MiniDV tape!!!
From: subirs-ga on 05 Jun 2004 22:10 PDT
Thanks for the comments! Appreciate it! I don't mind spending a few
hundred dollars...I might start thinking if it exceeds a thousand
dollars. The problem is I cannot find a commercial service to help me
with this recovery??!

Thanks again for the comments!
Subject: Re: Need HELP recovering recorded-over clip from MiniDV tape!!!
From: iang-ga on 08 Jun 2004 05:10 PDT
I'm sorry to hear about your problem, but I doubt that any recovery's
possible at a sensible price, and maybe not at all.  This list might
help though

Good luck!

Ian G.
Subject: Re: Need HELP recovering recorded-over clip from MiniDV tape!!!
From: ldavinci-ga on 10 Jun 2004 14:51 PDT
Hi subirs-ga,

  I am sorry to hear that you've lost your precious footage.  I am SURE you
could get it back.  This is based on the assumption that you could get back
your disk data even after overwriting several times. It is also due to the
physical property of the magnetic material and the nature of data(digital).
To get you an idea how this recovery is possible, you need to understand how
the data is being recorded, and being played back. The data is essentially a
continuos stream of 1's and 0's. An electrical voltage corresponding to your
1's and 0's gets stored into the magnetic material as alternating magnetic
pattern. When you play back, the magnetic patterns reproduces an equivalent
electical signal(but may not be of the same level as it was during recording).
Since it is digital, any voltage variation above a certain high value is
recognized as "1" and any voltage variation below a minimum value is recognized
as a "0". Once the digital values are recognized, they are "regenerated"(ie.
you get a value of say 5V instead of your actual 500uV from playback head and
you get a value of say 0.2V instead of the actual 50uV from playback head).
What happens when you overwrite?
The older values are overwritten with the new data(new magnetization). Also
there could be an erase head which tends to cleanup the tape before recording
(but I doubt that it may not be present just to reduce cost of the video camera
since the digital data does not need a clean demagnetized tape for recording).
So, what you will see now as new voltage from the actual playback head could
be say 475uV on places where the previous data was a "0" and close to 500uV
when the old data is "1", when the overwritten data is "1". You could similarly
figure out the voltage level for previous data with value of "0" overwritten
by a "0" or "1".  But the problem here is that the output circuit from the
player "regenerates" the value if it is above or below a certain threshold
say whatever voltage above 400uV is output as 5V and whatever value less than
100uV is output as 0.2V. The situation becomes even more complex as you
overwrite the data multiple times(luckily this is not your case).
So, inorder to get hold of the old data, you need to get access to the raw
voltage level from the playback head, then have a programmable circuit threshold
to identify these overlaps to generate/seperate the old data.  This amounts 
to having required electronics skills to do the same.  You should be able to 
do it cheap, if you could find someone proficient in working with the internal
circuit of these devices(a repair shop owner who likes to help you).  
You could also do it yourself at much lesser cost than what you would pay for
a recovery service otherwise, if you have a bit of electronics knowledge and
don't mind investing on the needed test equipments.  Let me know, if you 
need further assistance regarding the same.  But before any decision, 
first identify if your "camcorder" had an erase head.  This could help decide 
if you could do this yourself, or need a professional recovery service.

Subject: Re: Need HELP recovering recorded-over clip from MiniDV tape!!!
From: steph_evrard-ga on 21 Dec 2004 05:11 PST
Hi subirs-ga,

I happen to be in the exact same situation !
Did you find anything since you asked the question ?

Subject: Re: Need HELP recovering recorded-over clip from MiniDV tape!!!
From: subirs-ga on 21 Dec 2004 06:52 PST
Hi steph_evrard-ga,

No! Nothing as yet. Most of the research I conducted led me to believe
that the technology to recover does not exist.....maybe only in a lab,
somewhere??!!I've kept the tape the hope that one day
soon after we put a man (or woman!) on Mars, they might release the
technology to recover overwritten DV tapes.

In all seriousness, there is only a very, very small possibility that
we will ever recover the clips. The prime reason being that the
limited market for tape/data recovery does not drive technological
innovation in that direction.


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