This video, via Joakim Floke, demonstrates why – even after three decades – the Ensoniq SQ-80 is still a sought-after synthesizer.
The SQ-80 has a fairly comprehensive synth engine, combining digital oscillators with analog filters.
But what really makes it stand out is its expressive keyboard, which implements polyphonic aftertouch. Polyphonic aftertouch means that you can press down harder on individual keys to control synth parameters in an expressive way. In Floke’s demo, he uses this capability to modulate the position and filter cutoff of individual notes within a chord.
Unfortunately, polyphonic aftertouch is an option that adds to the costs of creating keyboards, and it remains a rare option to this day.
Here’s another example, demonstrating how polyphonic aftertouch can be used expressively, via synthylover: