;nyquist plug-in
;version 3
;type process
;categories "http://lv2plug.in/ns/lv2core#DelayPlugin"
;name "Delay..."
;action "Applying Delay Effect..."

;; by Steve Daulton, July 2012.
;; based on 'Delay' by David R. Sky
;; Released under terms of the GNU General Public License version 2:
;; http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
;;
;; For information about writing and modifying Nyquist plug-ins:
;; http://wiki.audacityteam.org/wiki/Nyquist_Plug-ins_Reference

;control delay-type "Delay type" choice "regular,bouncing ball,reverse bouncing ball" 0
;control dgain "Delay level per echo (dB)" real "" -6 -30 1
;control delay "Delay time (seconds)" real "" 0.3 0 5
;control pitch-type "Pitch change effect" choice "Pitch/Tempo,LQ Pitch Shift" 0 
;control shift "Pitch change per echo (semitones)" real "" 0 -2 2
;control number "Number of echoes" int "" 5 1 30
;control constrain "Allow duration to change" choice "Yes,No" 0 


;; The default pitch shift effect is a simple resampling, 
;; so both pitch and tempo of the delayed audio will change 
;; [as in Audacity's Change Speed effect].
;; LQ Pitch Shift (Low Quality) changes the pitch without 
;; changing the tempo, but the sound quality is not very good 
;; and tends to cause a short echo effect which can be quite 
;; noticeable on percussive sounds though may be acceptable 
;; on other sounds.

(setf err "")   ; initialise error message

(defun err-chk (arg min max)
  (if (or (< arg min) (> arg max))
    T nil))

(when (err-chk number 1 50)(setq err (format nil
  "Number of echoes '~a' outside valid range 1 to 50.~%~a"  
  number err)))

(when (err-chk shift -12 12)(setq err (format nil
  "Pitch change '~a' outside valid range -12 to +12 semitones.~%~a" 
  shift err)))

(when (err-chk delay 0 10)(setq err (format nil
  "Delay time '~a' outside valid range 0 to 10 seconds.~%~a" 
  delay err)))
 
(when (err-chk dgain -30 6)(setq err (format nil
  "Delay level '~a' outside valid range -30 to +6 dB.~%~a" 
  dgain err)))


;;; anti-alias low pass filter
(defun lp-wall (sig freq)
  (do ((count 0 (1+ count))
       (freq (* 0.94 freq)))
      ((= count 10) sig)
    (setf sig (lowpass8 sig freq))))


;;; Change speed
(defun change-speed (sig shift)
  (if (= shift 0)                               ; no pitch shift
    sig
    (let ((ratio (expt 0.5 (/ shift 12.0))))   ; shift value as frequency ratio
      (force-srate *sound-srate* 
        (stretch-abs ratio (sound sig))))))


;;; pitch shift audio 
(defun p-shift (sig shift)
  (if (= shift 0)                               ; no pitch shift
    sig
    (let ((sig (force-srate 44100 sig))         ; pitshift quality best at 44100
          ; anti-alias filter frequency
          (minrate (* 0.5 (min *sound-srate* 44100)))
          (ratio (expt 0.5 (/ shift -12.0))))   ; shift value as frequency ratio
      (force-srate *sound-srate*                ; convert back to correct rate
        (progv '(*sound-srate*) (list 44100)    ; pitshift requires rates to match
          (cond 
            ((> shift 5)                        ; reduce aliasing
              (pitshift (lp-wall sig (/ minrate ratio)) ratio 1))
            ((< shift -2)
              (pitshift (hp sig 20) ratio 1))   ; reduce sub-sonic frequencies
            (T (pitshift sig ratio 1))))))))

;;; apply effects to echo
(defun modify (sig num gain shift p-type)
  (let ((gain (db-to-linear (* num gain)))
        (shift (* num shift)))
    (if (= p-type 0)
        (mult gain (change-speed sig shift))
        (mult gain (p-shift sig shift)))))

;;; compute echoes
(defun delays (sound gain delay shift num type mod)
  (let ((echo (s-rest 0)))
    (do ((count 1 (1+ count))
         (dly 0))
         ((> count num)(sim echo sound))
      (setq dly 
        (case type
          (0 (+ dly delay))
          (1 (+ dly (* delay (- (1+ num) count))))
          (2 (+ dly (* delay count)))))
      (setf echo (sim
        (at 0 (cue echo))
        (at-abs dly
          (cue (modify sound count gain shift mod))))))))

(defun constrain-abs (sig dur)
  (extract-abs 0 dur (cue sig)))

;;; return errors or process
(if (> (length err) 0)
  (format nil "Error.~%~a" err)               ; return error
  (let* ((delay (if (= delay-type 0) delay (/ delay number)))
         (output 
          (multichan-expand #'delays 
            s dgain delay shift number delay-type pitch-type)))
    (if (= constrain 1)
      (multichan-expand #'constrain-abs output (get-duration 1))
      output)))
