;; a "normal scheme" temporal recursion
;; for event level control
(define loop
(lambda (time freq dir)
(change_freq
(* 1.0 (random 100 500))
(* 1.0 freq))
(callback time 'loop (+ time (* 20.0 freq))
(dir freq 50.0)
(cond ((> freq 600.0) -)
((< freq 300.0) +)
(else dir)))))