Re: [ARSCLIST] Fw: [78-l] ^ Distortion on a cassette tape

["Richard L. Hess" <arclists@xxxxxxxxxxxxxxx>]

OY! this sounds like no fun, and Norman gets a Purple Reel award for 
his efforts! Here is a story of my bout with one of these about ten 
months ago, and additional thoughts on what's behind it.

I had a similar tape. It was nominally recorded 4-track 15/16 in/s 
and the four tracks had to stay in sync.

What appeared to have happened to this tape was the mechanism 
dragged--there was something jamming it or something like that. It 
was very jumpy, especially at the slower speeds.

How I did it (it was a court reporter's tape), was I copied the tape 
at 3.75 in/s into the computer at 88.2 ks/s. I slowed it down to 
22.05 ks/s and then resampled that to 44.1 ks/s. This was necessary 
because the only 4-channel cassette machine I have is a Teac 234 
which runs only at 3.75 in/s.

So, once I had it in the computer, I played it back out (there was 
nothing I had in the computer that would do speed shifting of four 
channels in sync) to my Sony APR-16 16-track 1-inch recorder with the 
1/2-inch 4-track  heads on it, and recorded the defective portions at 30 in/s.

I then re-recorded this back into the computer while running the 
varispeed down, first all the way to 15 in/s. I then set the machine 
to 15 and ran the varispeed down to 12 before it was over. By that 
time the audio was pretty gratchy as you described.

Then I downsampled to 22.05 (my RME MultiFace doesn't go below 44.1), 
and then played it out at 88.2 back to the Tascam 234 Cassette. The 
client paid me and never said "boo."

I really think the slow stuff is so far out of spec and probably such 
uneven movement by the time it gets there that it will always be 
impossible to properly recover something that is going so slowly. The 
mechanical system of the recorder is in distress and is hunting and 
moving in fits and starts.

I think only parts of the conversation end up recorded at that time. 
Think about stiction or stick slip. The tape moves, then it doesn't, 
then it moves, then it doesn't. And there's acceleration and 
deceleration time involved, it's not instantaneous. This is why you 
cannot fix stiction artifacts on playback. This is an example of 
stiction during record, I suspect.

Anyone involved in this work will find tapes from broken machines 
that people want to recover. I had a reel that was broken, too, and 
the guy wanted the exact pitch of his parents' voices from the phone 
call. I still have it, and hopefully someday I'll be able to resolve 
the low-level hum on the tape...I'm not holding my breath.

I hope that helps a bit...

It's a good story! And yes, I spent more time on both of these 
projects than I got paid for. I like to solve the problems and get it done.

Cheers,

Richard

At 10:47 PM 6/21/2006, steven c forwarded:
> ----- 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^}
> >
> ...snip
> > 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?
> >
> >

Richard L. Hess                   email: richard@xxxxxxxxxxxxxxx
Aurora, Ontario, Canada       (905) 713 6733     1-877-TAPE-FIX
Detailed contact information: http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.