Spiegel plays the Bell Labs Digital Synthesizer, an experimental additive synthesizer designed by Harold G. Alles and Douglas Bayer at Bell Labs in 1977-78.
Here’s how Spiegel summarizes Improvisation On A Concerto Generator:
This composition was commissioned by Bell Labs and the Motion Picture Academy for the 50th anniversary of talking pictures.
Working with the Alles synthesizer, with its extensive array of input and output channels for control, was a real pleasure after years of GROOVE’s extreme restrictions.
The interactive software I wrote for this composition recycles the player’s keyboard input into an ongoing accompaniment. However, writing the software from a remote DEC PDP-11 computer (see also the PDP-11 FAQ and PDP Music Survey) in the new ‘C’ computer language still undergoing frequent change, within a still-experimental UNIX operating system, without the control inputs or sonic output, under a tight deadline, while the Alles synthesizer hardware was still under construction, turned out to be quite an adventure.