Digital Master vs DVCAM for HDV

[Winsordawson]

Scott, that is a great idea! Do you believe the magnets listed in the video above are adequate for this kind of job? While you said that DV/DVCam/DVCPro tapes would require a stronger magnet than a VHS, it seems that the "MagnetMan" used a stronger magnet on the VHS, on account of it larger size.

I also help out with a company where the client is "us," since the people being recorded are not paying for the tapes. However, since we do not pay them either (it's a mutual agreement), we would keep the tapes. I guess in this case we would still be stuck with them, since it seems DV tapes are more flimsy than I previously thought, and cannot withstand the same abuse as a VHS. I do not know if another magnetic layer in DigitalMasters would help.

[Cornucopia]

Scott, that is a great idea! Do you believe the magnets listed in the video above are adequate for this kind of job? While you said that DV/DVCam/DVCPro tapes would require a stronger magnet than a VHS, it seems that the "MagnetMan" used a stronger magnet on the VHS, on account of it larger size.

I also help out with a company where the client is "us," since the people being recorded are not paying for the tapes. However, since we do not pay them either (it's a mutual agreement), we would keep the tapes. I guess in this case we would still be stuck with them, since it seems DV tapes are more flimsy than I previously thought, and cannot withstand the same abuse as a VHS. I do not know if another magnetic layer in DigitalMasters would help.

NO! Most of those magnets are a joke. And that guy doesn't know half as much about magnetic recording as he ought to. "Magnet Man" indeed...

Magnetic recording uses Hi Frequency AC bias, and any TRUE demagnetizer also has to have an AC bias in order to work.

Think about this analogy...

You have an audio signal that runs in terms of amplitude per sample:
0...64...128...192...256...192...128...64...0...-64...-128...-192...-256...-192...-128...-64...0 (and on and on).
For those that know audio, you know this as an equal-width sawtooth wave, rich in even harmonics.
This isn't recorded on the tape that way, it's more like:
300,000...364,000...428,000...492,000...556,000... 492,000...428,000...364,000...300,000...236,000... 172,000...108,000...44,000...108,000...172,000...2 36,000...300,000.....
As you can see, if you LOWERED the signal by a DC amount, it would still have (nearly) the same identifiable wave pattern in the signal, just each would start at a lower level.

That's why broadcast degaussers use A) VERY, VERY strong magnets B) Hi-frequency Electromagnets C) usually a tractor belt to move the tapes through evenly.

The guy's bit about each recording looking clean is inadequate also, because he fails to mention that EVERY normal recorder on the planet also has erase heads that pass through the signal path prior to the record heads, specifically to bring the level back to (close to) ZERO before recording starts on that segment.

Without properly both electomagnetically degaussing AND using pre-erase, it is quite possible to record clip A, then "erase" and/ record clip B, and then with the proper tools, still be able to successfully read clip A. This is made more likely the higher the retentivity and particularly with the more recent digital formats that have tracks of alternating azimuth and code sequence patterns. I've witnessed it with D1 and Digibeta tapes.

So, pay the money and get the right tool for the job, I say.

BTW, DV tapes are smaller and slightly thinner, but they're really not much MORE fragile. Unravel & crinkle up either one and they're both toast.

Scott

[Winsordawson]

Thank you for the thorough explanation, for myself and future readers. Now I see why my broadcast VHS degausser will not be adequate for anything with a higher retentivity. So his gauss level/measurement routine seemed to be irrelevant. Maybe I should warn others on that site!!!! In regards to the fragility, I don't know, since others like LordSmurf have said that DV is filmy compared to VHS.