;nyquist plug-in
;version 4
;type process spectral
;preview linear
;name "Spectral edit parametric EQ..."
;action "Filtering..."
;author "Paul Licameli"
;copyright "Released under terms of the GNU General Public License version 2"

;; SpectralEditParametricEQ.ny by Paul Licameli, November 2014.
;; Updated by Steve Daulton 2014 / 2015.
;; Released under terms of the GNU General Public License version 2:
;; http://www.gnu.org/licenses/old-licenses/gpl-2.0.html

;control control-gain "Gain (dB)" real "" 0 -24 24

(defun wet (sig gain fc bw)
  (eq-band sig fc gain (/ bw 2)))

(defun result (sig)
  (let*
      ((f0 (get '*selection* 'low-hz))
       (f1 (get '*selection* 'high-hz))
       (fc (get '*selection* 'center-hz))
       (bw (get '*selection* 'bandwidth))
       (tn (truncate len))
       (rate (snd-srate sig))
       (transition (truncate (* 0.01 rate)))  ; 10 ms
       (t1 (min transition (/ tn 2)))         ; fade in length (samples)
       (t2 (max (- tn transition) (/ tn 2)))  ; length before fade out (samples)
       (breakpoints (list t1 1.0 t2 1.0 tn))
       (env (snd-pwl 0.0 rate breakpoints)))
    (cond
      ((not (or f0 f1)) ; This should never happen for a 'spectral' effect.
          (throw 'error-message (format nil "~aPlease select frequencies." p-err)))
      ((not f0)
          (throw 'error-message (format nil "~aLow frequency is undefined." p-err)))
      ((not f1)
          (throw 'error-message (format nil "~aHigh frequency is undefined." p-err)))
      ((and fc (= fc 0))
          (throw 'error-message (format nil "~aCenter frequency must be above 0 Hz." p-err)))
      ((and f1 (> f1 (/ *sound-srate* 2)))
          (throw 'error-message
            (format nil "~aFrequency selection is too high for track sample rate.
                        For the current track, the high frequency setting cannot~%~
                        be greater than ~a Hz"
                    p-err (/ *sound-srate* 2))))
      ((and bw (= bw 0))
          (throw 'error-message
            (format nil "~aBandwidth is zero (the upper and lower~%~
                         frequencies are both ~a Hz).~%~
                         Please select a frequency range."
                    p-err f0)))
      ;; If centre frequency band is above Nyquist, do nothing.
      ((and fc (>= fc (/ *sound-srate* 2.0)))
          nil)
      (t  (sum (prod env (wet sig control-gain fc bw))
               (prod (diff 1.0 env) sig))))))

(catch 'error-message
  (setf p-err "Error.\n")
  (if (= control-gain 0)
      nil ; Do nothing
      (multichan-expand #'result *track*)))