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$nyquist plug-in
$version 4
$type process
$name (_ "Limiter")
$manpage "Limiter"
$debugbutton false
$action (_ "Limiting...")
$preview enabled
$author (_ "Steve Daulton")
$release 2.3.0
$copyright (_ "Released under terms of the GNU General Public License version 2")
;; limiter.ny by Steve Daulton November 2011, updated May 2015.
;; 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 type (_ "Type") choice (
("SoftLimit" (_ "Soft Limit"))
("HardLimit" (_ "Hard Limit"))
;i18n-hint: clipping of wave peaks and troughs, not division of a track into clips
("SoftClip" (_ "Soft Clip"))
("HardClip" (_ "Hard Clip"))
) 0
$control gain-L (_ "Input Gain (dB)
mono/Left") real "" 0 0 10
$control gain-R (_ "Input Gain (dB)
Right channel") real "" 0 0 10
$control thresh (_ "Limit to (dB)") real "" -3 -10 0
$control hold (_ "Hold (ms)") real "" 10 1 50
$control makeup (_ "Apply Make-up Gain") choice (
(_ "No")
(_ "Yes")
) 0
(if (not (boundp 'type))
(setf type 0))
(if (boundp 'gain-L)
(setf gain-L (db-to-linear gain-L))
(setf gain-L 1))
(if (boundp 'gain-R)
(setf gain-R (db-to-linear gain-R))
(setf gain-R 1))
(if (boundp 'thresh)
(setf thresh (db-to-linear thresh))
(setf thresh (db-to-linear -3.0)))
(if (not (boundp 'hold))
(setf hold 10.0))
(if (boundp 'makeup)
(if (= makeup 1) (setf makeup T) (setf makeup nil))
(setf makeup nil))
;;; brick wall limiter
(defun hardlimit (sig limit hld)
(let* ((time (/ hld 3000.0)) ; lookahead time (seconds)
(samples (round (* time *sound-srate*))) ; lookahead in samples
(peak-env (get-env sig samples time limit)))
(mult sig
(snd-exp
(mult -1 (snd-log peak-env))))))
;;; Envelope follower for brick wall limiter
(defun get-env (sig step lookahead limit)
(let* ((sig (mult (/ limit) sig))
(pad-time (* 3 lookahead)) ; padding required at start (seconds)
(pad-s (* 3 step)) ; padding smaples
(padding (snd-const (peak sig pad-s) 0 *sound-srate* pad-time))
(peak-env (snd-avg sig (* 4 step) step OP-PEAK)))
(extract 0 1
(s-max 1
(sim padding
(at-abs pad-time (cue peak-env)))))))
(defun softlimit (sig thresh hld)
(let* ((sig (hardlimit sig 1 hold))
(step (truncate (* (/ hld 3000.0) *sound-srate*)))
(waveshape (snd-avg sig (* 4 step) step op-peak))
(env (sum thresh (mult thresh (diff 1 waveshape))))
(env (clip env 1))
(offset (/ (* 3 step) *sound-srate*))
(initial (peak sig (* 2 step)))
(pause-lev (sum thresh (mult thresh (diff 1 initial))))
(pause-lev (clip pause-lev 0.9))
(pause (snd-const pause-lev 0 *sound-srate* offset)))
(setf env
(sim
pause
(at-abs offset (cue env))))
(mult sig env)))
(defun soft-clip-table ()
"Lookup table for soft clipping wave-shaper"
(abs-env
(sound-srate-abs 44100
(Control-srate-abs 44100
(let* ((knee (- 1 (/ 1.0 pi)))
(kcurve (mult knee (osc (hz-to-step (/ (* 4 knee))) knee)))
(ikcurve (mult knee (osc (hz-to-step (/ (* 4 knee))) knee *sine-table* -90)))
(lin (pwlv -0.5 knee -0.5
(+ knee (/ 2.0 pi)) 0.5
2.0 0.5
2.0 (+ 0.5 knee)
2.1 (+ 0.5 knee))))
(mult (/ 2.0 pi)
(sim
(at-abs 0 (cue ikcurve))
(at-abs 0 (cue lin))
(at-abs (+ knee (/ 2.0 pi)) (cue kcurve)))))))))
(defun soft-clip (sig)
(let* ((knee (- 1 (/ 1.0 pi)))
(clip-level (* (+ 0.5 knee)(/ 2.0 pi)))
(sig (mult clip-level (/ thresh) sig)))
(if makeup
(mult 0.999
(/ clip-level)
(shape sig (soft-clip-table) 1.0))
(mult thresh
(/ clip-level)
(shape sig (soft-clip-table) 1.0)))))
(defun makupgain (sig)
(if makeup
(mult (/ 0.999 thresh) sig) ;keep below 0dB
sig))
;; Pre-gain
(setf *track*
(if (arrayp *track*)
(vector (mult (aref *track* 0) gain-L)
(mult (aref *track* 1) gain-R))
(mult *track* gain-L)))
(case type
(0 (makupgain (multichan-expand #'softlimit *track* thresh hold)))
(1 (makupgain (multichan-expand #'hardlimit *track* thresh hold)))
(2 (soft-clip *track*))
(T (makupgain (clip *track* thresh))))