Anyone ever send a track to a tape recorder then back?

[SouthSIDE Glen]

I still come across statements that say that there may or may not be residual buildup in the heads that cause a noticeable difference in playback. I just read an article from UCLA that says erase heads don't need demagnetizing. I have seen one that says record heads don't need it either because as soon as you turn it on it is a magnet again. The bias and gap do seem to have much more a contribution and the residual flux diminimus.

Concentrate on the playback heads, which are not supposed to impart any flux of their own. This will let you look at the magnetization issue without extra complication.

Hard or soft, there is always going to be some hysteresis in any part of the head assembly that can be affected at all by a magnetic flux. Repeated exposure (and even some small amount of constant exposure) from a biased magnetic flux before returning to hyseretical randmoness in that material will cause a slow buildup in the level of hysteresis. Rather like a gallon jug that has a hole in it that drains water at a rate of a milliter an hour. Fill it up at an averall average rate of a milliter and a half an hour, and even with the hole, the jug will eventually fill up.

Some say that there is no overall bias positive or negative in the flux coming from the tape. They argue that the overall statistical average bias will be zero, and therefore that statistically there is no overall magnetic build-up on the playback head (the domains stay relatively random.) Others say that fact is mitigated by the fact that the tape only travels in a single direction (on non-auto-reverse machines) that it tends to orient the head domains in the direction favored by the direction of tape travel. I am honestly not sure 100% on this issue, but I do know that when creating a homemade compass needle, one should rub the magnet agaist it in a single direction to integrate and strengthen magnetic orientation. So I suspect that a similar principle may be in effect on tape machines. Maybe someone else knows more about that issue.

In your article stating "a magnetized recording head will decrease the signal to noise ratio 6 to 10 db. Also it will gradually erase the high frequencies during playback.", does it mean residual?

I'm not sure what you mean by the question "does it mean residual?", btu the way I view that issue is that a magnetic buildup on the playback head is kind of like an analog magnetic version of what dithering is to digital signals. The analogy is not exact, but I think it's close.

The transfer of magnetic flux works in both directions, it plays no favorites. If/when there is a magnetic buildup on the playback head, that can, in turn, go back and affect any tape passed over it. It is, in effect, acting like a very weak version of an erase head, except that it is MUCH weaker, and it is magnetically biased. This (as I understand it) has the effect of laying low-level, high frequency noise over the tape signal, reducing both the S/N ratio and the high frequency response.

I still believe that demagnetizing the heads is unnecessary and if done incorrectly it will end up polarizing them.

The second part is certainly true. Improper use of a demagnetizer can wind up magnetizing the heads worse instead of properly randomizing them.

As for the first one, I agree with MCI when he suggests that says demagging is often overdone. However, done correctly, that overdoing should not be harmful; it's just not necessary.

I kind of view it like changing the fluids in a car. Cleaning the tape path is like changing the oil. Demagging is like changing the trans fluid. I change my oil every 3000 miles or so, but changing trans fluid is only really a useful idea once for every 10 or 15 oil changes. You can do it more often than that, but if your car is in decent running order, you're probably just throwing your money away.

Finally, I'd also add that demagging is not just something that exists in audio. It's also something that was/is part of regular maintenance schedules in data processing centers that used to use extensively use tape machines for data I/O and storage. Back in my mainframe computer operator days we used to schedule head demagging of our tape drives on a minimum but not that frequent rotation (not counting emergency maintenance.) How much it may have helped may be debatable, but it certainlty didn't hurt.

G.

 

[cusebassman]

You can't stack on over 1 pre-amp stage or you will blow up the console (Revolution used 4 stages!)

And that song sounded like crap Guess they should've only used one stage on those guitars