Example 1. Creating MIDI pitch bends.

;;; max bend down
(new midi-pitch-bend :time 0 :channel 3 :bend -8192) 

;;; cancel bend
(new midi-pitch-bend :time 1 :channel 3 :bend 0) 

Example 2. Determining pitch bend values.

(define (step->bend value . width)
  ;; convert a value between +-width to a pitch
  ;; bend value ranging from -8192 to 8191
  (inexact->exact
   (floor (rescale value (- width) width -8192 8191))))

;;; bend one quarter-tone down (whole step max)
(new midi-pitch-bend :bend (step->bend -.5 2))

;;; percentage bend
(new midi-pitch-bend :bend (step->bend 75 100))

Example 3. Musical process generating random bends.

(define (ranbends num dur )
  ;; output num bends dur apart, last bend 0.
  (process for i from 1 to num
           for b = (between -2.0 2.0)
           output (new midi-pitch-bend :time (now)
                      :bend (if (= i num)
                              0
                              (step->bend b)))
           wait dur))

(define (random-bends reps )
  (process repeat reps
           for key = (between 30 90)
           for dur = (pick 1 2 3)
           for num = (between 2 8)
           for inc = (/ dur (+ num 1))
           output (new midi :time (now)
                      :duration dur
                      :keynum key)
           ;; sprout num bends starting inc ahead
           sprout (ranbends num inc) at (+ (now) inc)
           wait dur))

(events (random-bends 20) "test.mid")
⇒ "test.mid"