696899414)
:(samps 9131)
(129.273696899414 130.094696044922 0.256685614585876 -0.564319849014282 129.530380249023)
:(samps 9132)
(129.530380249023 130.108947753906 -0.25042849779129 -0.828995883464813 129.27995300293)


we can use the phase to minimize the difference with the sum:

(define (feedbk beg dur freq amp index iters pha1)
  (let* ((start (seconds->samples beg))
	 (end (+ start (seconds->samples dur)))
	 (y 0.0)
	 (x-incr (hz->radians freq)))
     (do ((i start (+ i 1))
          (x 0.0 (+ x x-incr