Homework #6:

Scheme Code:

(define lpfilter  ; IIR version, aka feed-back or recursive delay
     (lambda (secs att samps bz)
            (let ((del (make-delay (round (* secs (srate)))))
                  (del1 (make-delay samps))
                  (yz 0.0)                                                     ; use yd, i.e., send output to delay
                  (y0 0.0)
                  (yu 0.0)
                  (yx 0.0)
                  (a0 0.5))
           (lambda (x0)
                   (set! yz (tap del))                                 ; where it comes back from delayline
                   (set! y0 (+ x0 (* att yz)))
                   (set! yx (tap del1))
                   (delay del yu)
                   (set! yu (- (* a0 y0) (* bz yx)))
                   (delay del1 yu)                                      ;feed into delayline
                   yu)
              )))

(click 0.3)

(map-chan (lpfilter .0032 .85 1 -.5))    --- filter tube
(map-chan (lpfilter .0032
 

Tube Sound:

 Sound File

 Sonogram

String Sound:

 Sound File

 Sonogram