It was in the late 1970s, long before MIDI interfaces existed for musical instruments,
that Superscope developed an electromechanical self-playing system for pianos.
The system used digitally recorded tape cassettes to control the pianos. These tapes
were played at double speed in order to process the amount of data required.

The PT-150, which was largely identical in appearance to the SD 3000 tape deck, was
used  to create digital recordings, which were then played back on a smaller Superscope
player that was directly connected to the mechanism used to play the pianos.
At least, this is the information I was able to research on the Internet myself.

The real difference between the SD 3000 and the PT-150 is not just the different
labeling of the controls and the data cable connection on the back. If you remove
the cover of the PT-150, you will immediately notice numerous computer chips,
whereas the SD 3000 only has conventional analog electronics unter it’s lid.

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