Jody Kravitz wrote:

> 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

This was marketed to the vision-impaired folks so they could tape
lectures at normal speed, then play them back at higher speed
without changing the voice pitch. The head spun in the direction
of travel, and had the effect of chopping the sound into short
bursts and lengthening each burst to reduce the pitch. Sound
between the bursts was lost, but speech is very redundant so the
intelligibility remains.

see, for example:

    http://sightconnection.site.yahoo.net/sightconnection/plu-331.html

Marc Kaufman