Equipment

Swarmatron

John Cale used this hand-built instrument, an analogue synthesizer made by Leon and Brian Dewan, on Time Stands Still on the Mercy album. From Wikipedia:

The distinctive feature of the Swarmatron is its use of eight individual oscillators controlled monophonically, switchable between sine and sawtooth waves. These oscillators produce an equidistant chord, where their spacing is under the player's immediate control. The oscillators may be switched on and off individually by a row of switches.

A fingerboard synthesizer like the Trautonium or Tannerin, a finger is placed or slid from side to side along a ribbon controller to control the pitch. This allows for easy Glissandi, which can be used to achieve smooth rises and falls in the pitch of the instrument. Careful finger placement may be used to play discrete notes similar to the operation of an unfretted or bowed string instrument such as a violin. Due to its adjustable nature, ribbon controller is unlabeled, although some players compensate for this by marking note positions.