it's long-ish, but basically split into two parts...the first half is about how this can be done easily on stringed instruments, and the second half (about 13:30 or so in), I use a couple of Player devices to help me do it for the keyboard--a Note Echo, and a custom-built Delta MIDI Computer patch.
here's the Delta patch, for anyone interested in checking it out:
https://drive.google.com/file/d/14w9EqP ... sp=sharing