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MMD > Archives > September 1999 > 1999.09.19 > 11Prev  Next


Rotating Heads for Audio Tape
By Mark Kinsler

>  [ While I was working at the University of Illinois School of Music
>  [ (as a computer consultant, not a musician or composer), I recall
>  [ reading about an audio recorder that had a rotating head that
>  [ made it possible to change playback speed without altering
>  [ pitch, or conversely change pitch without altering playback
>  [ speed.  This special effect came with a price -- a sort of
>  [ burbling distortion in the playback, but it was adequate for
>  [ compressing speech for "books on tape" and the like.  I never
>  [ saw a drawing for this and don't know if it would play standard
>  [ linearly recorded tapes or if it had to be used on tapes it
>  [ made.  Does anyone know about this device ?  Thanks.  --Jody

Most likely it could only play tapes that it had recorded.  There have
been a few rotating-head audio recorders, the purpose of the rotating
head being almost invariably to save tape.  The head rotates quite
slowly, and the tape, which might be 3/4" wide video-type tape, moves
along so slowly as to be almost imperceptible.

You'll find these in communications rooms of police and fire stations,
where they're used to record everything that's said over both wire and
radio communications systems.  Radio stations also use them for logging:
instead of having a guy write down what advertisements were run and
when, they just record and save everything that goes out over the air
on a reel of tape.

I imagine that some digital techniques have been adopted to improve the
compression in recent years.

There were indeed video recorders without rotating heads.  One notable
attempt was a British home video recorder from the 1960's which ran the
tape at something like 60 inches per second and which made an
incredible mess if the tape broke, which it sometimes did.

Another attempt, which was a masterpiece of engineering but a marketing
failure, was a camcorder developed by Fisher-Price, the toy company,
around 1987 (???).  It used a standard audio cassette, but recorded it
at full width and high speed.  I think a 90 minute cassette had a
recording time of 7 minutes.  Camera and monitor were monochrome.  The
fellow at a fancy toy store in New York told me that the picture
quality was too low: the impression that I got was that the rich kids
that formed their customer base were already using their parents'
camcorders by then.

Mark Kinsler

Athens, Ohio, USA.  Home of the "How Things Work" educational program.
See http://www.frognet.net/~kinsler


(Message sent Sun 19 Sep 1999, 21:02:19 GMT, from time zone GMT-0400.)

Key Words in Subject:  Audio, Heads, Rotating, Tape

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