exponential curves in CLM?

[To: Larry Troxler <lt@westnet.com>]

you can get as close as you like to a given exponential (i.e.
thinking in terms of e^(-kt)) by fiddling with the base:

(definstrument expins (dur k m)
  (let* ((nd (floor (* dur sampling-rate)))
	 (j 0)
	 (maxdiff 0.0)
         (zv (make-env (list 0 1 1 (exp (- k))) :base m)))
    (run* (maxdiff)
     (loop for i from 0 to nd do
       (let* ((vala (env zv))
	      (valb (exp (* (- k) (/ j nd))))
	      (valc (abs (- valb vala))))
       (outa i vala)
       (outb i valb)
       (if (> valc maxdiff) (setf maxdiff valc))
       (incf j))))
    (print maxdiff)))

;;; (with-sound (:channels 2) (expins 1 .5 1.65))
;;; 7.2419643e-5
;;; or
;;; (with-sound (:channels 2) (expins 1 5 148))
;;; 1.3118982e-4
;;;
;;; that is, let the envelope "base" be (exp k)