$nyquist plug-in
$version 4
$type process
$preview linear
$name (_ "Low Pass Filter")
$manpage "Low_Pass_Filter"
$debugbutton disabled
$action (_ "Performing Low Pass Filter...")
$author (_ "Dominic Mazzoni")
$copyright (_ "Released under terms of the GNU General Public License version 2")

;; lowpass.ny by Dominic Mazzoni

;; 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:
;; https://wiki.audacityteam.org/wiki/Nyquist_Plug-ins_Reference


$control frequency (_ "Frequency (Hz)") float-text "" 1000 0 nil
$control rolloff (_ "Rolloff (dB per octave)") choice (
   ("dB6" (_ "6 dB"))
   ("dB12" (_ "12 dB"))
   ("dB24" (_ "24 dB"))
   ("dB36" (_ "36 dB"))
   ("dB48" (_ "48 dB"))
) 0


(cond
  ((< frequency 0.1) (_ "Frequency must be at least 0.1 Hz."))
  ((>= frequency (/ *sound-srate* 2.0))
      (format nil (_ "Error:~%~%Frequency (~a Hz) is too high for track sample rate.~%~%~
                   Track sample rate is ~a Hz~%~
                   Frequency must be less than ~a Hz.")
              frequency
              *sound-srate*
              (/ *sound-srate* 2.0)))
  (T  (funcall (nth rolloff '(lp lowpass2 lowpass4 lowpass6 lowpass8))
               *track* frequency)))