Piano-Mode is a minor mode for Emacs that turns your keyboard into a “piano” keyboard. It is modeled after the same behavior commonly included in music trackers or digital audio workstations. Each “note on” (piano key press) event is sent to the function specified by the piano-key-down-function variable, and each “note off” is sent to the function specified by piano-key-up-function. See the included piano-mode-cl-collider.el for an example of functions that could be set for these variables.

Using use-package to load piano-mode and the piano-mode-cl-collider functionality:

(use-package piano-mode
  :custom
  (piano-key-down-function 'piano-cl-collider-play-note)
  (piano-key-up-function 'piano-cl-collider-release-note)
  :bind (("C-c k" . piano-mode)
         :map piano-mode-map
         ("\\" . piano-cl-collider-change-instrument)
         ("|" . piano-cl-collider-change-parameters))
  :config
  (require 'piano-mode-cl-collider))

Since (to the best of my knowledge) Emacs does not provide any way to differentiate between a user’s keystrokes and OS-generated key repeat events, and doesn’t expose key release events to Elisp at all, this mode uses the time between events to determine whether a key is still “pressed”. Obviously, this is a very hacky solution, so expect glitchy behavior to occur sometimes. You may want to tune the piano-key-repeat-delay and piano-key-repeat-rate variables based on your OS settings.

Right now, this will only work if you’re using a QWERTY keyboard layout, but you can edit piano-ascii-to-note-translation-table to match your keyboard layout. (Pull requests for alternate layouts are welcome!)

• “mono mode”
• record mode
• better heuristic for note auto-release; take into account whether the key is “repeating” or not.