This video, via Reuben Jones, offers a vintage synth demo of the Logan Vocalist, an Italian vocal synthesizer by Logan Electronics (1979).
The Logan Vocalist is an analogue synthesizer designed to mimic the sound of a polyphonic choir and the solo human voice. Vocal-like sounds are made using a mixture of hard-synced oscillators, analogue filtering, and ensemble and vibrato effects.
Jones notes, “There isn’t a lot of information on this rare and interesting synth, and the schematics are the only documents I can find. If anyone has more information, including the A3 folded manual that Peter Forrest mentions in his A-Z book, please let me know!”