Since ARSCLIST has all the serious magnetic tape expertise, perhaps you
can answer Norman's question (and I, or someone, can forward the solution
back over to 78-L...)
Steven C. Barr
----- Original Message -----
From: "Norman Field" <jazz@xxxxxxxxxxxxxxx>
To: "78-l" <78-L@xxxxxxxxxxxx>
Sent: Wednesday, June 21, 2006 1:10 PM
Subject: [78-l] ^ Distortion on a cassette tape
OK, it's well off topic, but there's a lot of expert folks up here. And
I'm
curious as to how this problem occurred.... somebody here may well know?
This C90 cassette (of speech) was recorded on a faulty machine, in that
it
began very slow, & then ran slower & ever slower.
In fact, it ended up so slow, that 32 minutes of one 45-minute side, when
roughly re-pitched, ran for about 75 minutes!
Of course, it started off like the Chipmunks... and ended up like
hyper-active Chipmunks breathing practically pure helium & rushing around
in
hopeless confusion... 8^}
The starting speed, when roughly halved, gave perfectly acceptable
results,
as was expected.
But: as the speed fell & fell, finally requiring ~100% pitch reduction, a
distortion gradually crept in.
So that by the end, the voices were fragmentary & broken, sounding like a
conversation half-heard in a dream, as it were. And totally
incomprehensible
of course.
Why should the material have become distorted?
If the cells in the cassette recorder were losing voltage, that would
account for it... but surely they'd never drive the motor for half an
hour
in that state?
The only thing I can come up with is that the tape was somehow
'saturated'
with signal, because it was passing far too slowly over the recording
head?
And yet the modulation level on the tape was very low...
Has anyone here come across such a phenomenon before?
Previously, I've recovered stuff recorded on reel tape at 15/16 ips (~2.4
cm/sec) when the lowest speed I have here is 3 3/4 ips (9.5 cm/sec),
which
requires a similar re-pitching, and it's been pretty well OK.
Norman.
P.S. At least I'm not charging my client for the 25% of the stuff I did
manage to recover. We here on this list, many of us the 'progeny' of John
R.T. Davies, don't like to be beaten! Come to that, I wonder what he
would
have done..?
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