On 01/18/2016 02:39 AM, Dave G4UGM wrote:
I know that tapes have different coatings, so some are ferrous and other chrome based, but what about the backing and "glue" that holds the two together?
The difference in coatings between digital and analog tapes is pretty profound, as is the method of recording.
Digital tapes want the magnetization characteristics to be as "steep" as possible, with the least middle ground (i.e. linear region).
Analog tapes want just the opposite--a wide linear (or nearly so) magnetization region. Audio tapes employ the use of "bias" (either AC or DC) to push the recording into the linear area as much as possible.
Backing for reel-to-reel magnetic tapes is almost always mylar/polyester, while audio tapes have used everything from paper and acetate to mylar. There's a good reason for that--acetate is inexpensive and performs well short-term. The problem is that it stretches rather than breaks under tension, which isn't acceptable in start-stop applications such as computer tape drives.
That's probably a good thing. Acetate based tapes degrade in an ugly manner--and enclosing the reel in an airtight case exacerbates the problem. You can tell the difference easily at this point in time by the pronounced "vinegar" smell of deteriorating cellulose acetate.
The binder and lubricants varied between manufacturers and were generally considered to be "trade secrets".
--Chuck
