We can play a monophonic synthesizer with lowest or highest note priority. The related VUGs are called MIDI-LOWEST-KEYNUM and MIDI-HIGHEST-KEYNUM. For example:

(in-package :scratch)

SCRATCH> (set-rt-block-size 1)

(dsp! highest-note-test ((chan fixnum) a d s r)
  "Highest priority monosynth (single trigger)."
  (with ((keynum (midi-highest-keynum chan)))
    (with-samples ((glide (exp-midi-cc chan 1 0.01 1.2))
                   (amp (midi-amp *linear-midi-table* chan keynum))
                   (amp-prev +sample-zero+)
                   (gate +sample-zero+))
      (if (zerop amp)
          (setf gate +sample-zero+ amp amp-prev)  ; Note off.
          (setf gate (sample 1) amp-prev amp))
      (stereo (* (envelope (make-local-adsr a d s r) gate 1 #'identity)
                 (gbuzz (lag (midi-cps *default-tuning* keynum) glide)
                        (lag amp 0.02) 20 1 .6))))))

SCRATCH> (rt-start)

SCRATCH> (defvar *midiin* (pm:open (pm:get-default-input-device-id)))

SCRATCH> (recv-start *midiin*)

SCRATCH> (highest-note-test 0 .1 0.9 .7 .1 :id 123)

         ;; Change attack and release times.
SCRATCH> (set-controls 123 :a .01 :r .02)

SCRATCH> (free 123)

SCRATCH> (recv-stop *midiin*)

SCRATCH> (rt-stop)

SCRATCH> (pm:terminate)

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