In MMD 990916 Jody asked 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.

In the years around 1970 I worked with one of those. The contraption was
a 1 ft cube wooden box containing a motor with a continuously variable
disc variator to drive a capstan/pinchroller and a drum about 2 inches
diameter carrying 4 reproducing heads. You put it on a stand as
vorsetzer to an ordinary Ampex studio recorder which provided the
amplification and handled the 1/4" single-track tape reels, normally
played at 15 IPS. Tapes were recorded the ordinary way, the device was
used only for playback.

You had to thread the tape differently depending on whether you wanted
speed or pitch change, using or bypassing the external drive capstan.
The tape went over 1/4 of the head drum such that essentially one head
at a time was in contact with the tape.

The device was made by a small German company whose name I cannot
recall. I will look in the attic of the lab if the thing is still there,
but I very much fear it has passed on. It was fairly quickly obsoleted
by modern developments that made the corresponding tricks using solid
state technology.

Indeed, the only patent I ever filed was based on this same principle
applied to restoration of the voice of divers breathing a helium-oxygen
mixture.

Johan Liljencrants