On Mon, 28 Apr 2014 14:54:39 +0100, "R. Mark Clayton"
wrote:


"Bill Wright" wrote in message
...
Katie, who is 11, was helping me in the workshop today. She told me how
some of her class been in trouble for filming the teachers covertly. Of
course I told her how, in 1965, I'd made a sound recording of our maths
teacher, with the class deliberately winding him up just to make it more
fun. I then found myself trying to explain about reel-to-reel tape
recorders. I could see that Katie just couldn't grasp the concept. Finally
she asked, "But how much memory did it have?"

A 1970' nine track tape deck [for a computer] - about 2Gb

Before they were phased out a DAT tape also held about 2Gb.

I've got a collection of 4GB DAT cartridges (uncompressed capacity)
along with the DAT backup drive which I'd picked up at a bargain price
of 200 quid perched in amongst the dusty collection of other such
detritus on top of a roller shutter cupboard in my home office cum
workshop.

I've even hung onto the Adaptec AHA 2940/2940U scsi adapter card (PCI
so still a doable 'add on' in a modern box - I thought it was an ISA
card until I had a closer look) which, fortuitously, has been acting
as a "Dust Cover" to prevent dust ingress through the vent holes and
carriage slide slots in the top of the drive casing.

Of course the recording on audio reel to reel recorders was analogue, so a
data capacity is not so meaningful.

The best you can do is estimate what it would require to digitise the
recordings with suitably matched sample rate and bit depth.

If it's a dolby encoded recording at 3 3/4 ips on Maxell UDB tape on
an excellent tape deck such as as a fettled ('cos it _was_ broken by
design!) Akai GX630DB reel to reel tape deck, a fair assumption would
be to use the CD based sample rate and bit depth to calculate its GB
equivilent of digital storage.

A 10 inch reel with 3,600 foot of tape at 3 3/4 ips gives a total
each way of 3 hours and 12 minutes which is a grand total of 384
minutes. A minute's worth of CD audio quality represents some
10.0937MiB's worth. translating the 384 minute figure gives us a total
of 3.785GiB. It's a rather sobering thought that the box used to store
that ten inch reel of tape would easily store thousands of 4GB microSD
cards!

Of course, an older metal headed tape recorder without dolby NR using
older tape formulations such as Scotch Dynarange and EMI tape using
the 3 3/4 ips speed[1] would only need a 32KHz sampling rate at 16
bits per sample (2.746GiB's worth).

In both cases, a conversion to a lossless compression format such as
FLAC will produce an even lower (but more accurate) memory equivilent.

[1] around the equivilent performance of a high quality cassette deck
with accurately aligned dolby level. Realistically, a C90 TDK SA tape
would only manage the equivilent of 700MiB of storage.
--
Regards, J B Good