exponential curves in CLM?

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

Perhaps this instrument will make it more obvious what
the exponential envelope segments are doing:

(definstrument expins (dur frq amp)
  (let* ((nd (floor (* dur sampling-rate)))
         (o1 (make-oscil frq))
	 (o2 (make-oscil frq))
	 (j nd)
	 (maxdiff 0.0)
         (zv (make-env '(0 1 1 0) :base 2.718)))
    (run* (maxdiff)
     (loop for i from 0 to nd do
       (let* ((vala (* amp (env zv) (oscil o1)))
	      (valb (* (/ amp (- 2.718 1.0)) (- (exp (/ j nd)) 1.0) (oscil o2)))
	      (valc (abs (- valb vala))))
       (outa i vala)
       (outb i valb)
       (if (> valc maxdiff) (setf maxdiff valc))
       (decf j))))
    (print maxdiff)))

#|
(with-sound (:channels 2 :statistics t) (expins 1.0 440.0 .5))
8.189678e-5 test.snd: 
  Duration: 1.0001, Last begin time: 0.0000
  Compute time: 0.338, Compute ratio: 0.34
  OutA max amp: 0.499 (near 0.001 secs)
  OutB max amp: 0.499 (near 0.001 secs)
|#