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https://github.com/cookiengineer/audacity
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175 lines
6.4 KiB
Common Lisp
175 lines
6.4 KiB
Common Lisp
$nyquist plug-in
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$version 4
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$type process
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$name (_ "Noise Gate")
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$manpage "Noise_Gate"
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$debugbutton false
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$preview enabled
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$author (_ "Steve Daulton")
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$release 3.0.1
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$copyright (_ "Released under terms of the GNU General Public License version 2 or later.")
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;; Released under terms of the GNU General Public License version 2 or later:
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;; http://www.gnu.org/licenses/old-licenses/gpl-2.0.html .
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$control mode (_ "Select Function") choice (("Gate" (_ "Gate"))
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("Analyze" (_ "Analyze Noise Level")))
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0
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$control stereo-link (_ "Stereo Linking") choice (("LinkStereo" (_ "Link Stereo Tracks"))
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("DoNotLink" (_ "Don't Link Stereo")))
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0
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;; Work around bug 2336 - Text after control is not read by screen reader.
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$control threshold (_ "Gate threshold (dB)") float "" -40 -96 -6
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$control gate-freq (_ "Gate frequencies above (kHz)") float "" 0 0 10
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$control level-reduction (_ "Level reduction (dB)") float "" -24 -100 0
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$control attack (_ "Attack (ms)") float "" 10 1 1000
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$control hold (_ "Hold (ms)") float "" 50 0 2000
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$control decay (_ "Decay (ms)") float "" 100 10 4000
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;; The gain envelope for the noisegate function may be a mono sound (stereo-link = 1, or *track* is mono)
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;; or an array of sounds (stereo-link = 0 and *track* is stereo).
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;; 'Level Reduction' is similar to "Range" or "Floor", but is a (negative) amount of gain
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;; rather than a fixed level.
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;;
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;; To create the gain envelope:
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;; 1. If stereo track and stereo-link = 1, get the max of left and right.
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;; 2. Add 'hold' when level > threshold.
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;; This adds a high level signal for 'hold' seconds when the level
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;; falls below the threshold.
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;; 3. Nyquist GATE function to generate exponential rise and decay.
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;; Unlike analog noise gates, lookahead is used so that the gate
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;; begins to open before the signal rises above the threshold.
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;; When the threshold is reached, the gate is fully open.
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;; This prevents the gate from clipping the beginning of words / sounds.
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;; 4. Scale level of envelope and offset so that we have unity gain above
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;; threshold, and 'level-reduction' below the threshold.
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;; If silence-flag is set (= 1), gain below the threshold is zero.
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; Global variables
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(setf silence-flag (if (> level-reduction -96) 0 1))
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(setf gate-freq (* 1000.0 gate-freq))
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(setf floor (db-to-linear level-reduction))
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(setf threshold (db-to-linear threshold))
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(setf attack (/ attack 1000.0))
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(setf lookahead attack)
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(setf decay (/ decay 1000.0))
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(setf hold (/ hold 1000.0))
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(defun error-check ()
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(let ((max-hz (* *sound-srate* 0.45)) ;10% below Nyquist should be safe maximum.
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(max-khz (roundn (* 0.00045 *sound-srate*) 1))
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(gate-freq-khz (roundn (/ gate-freq 1000.0) 1)))
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(when (>= gate-freq max-hz)
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;; Work around bug 2012.
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(throw 'err (format nil (_ "Error.
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\"Gate frequencies above: ~s kHz\"
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is too high for selected track.
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Set the control below ~a kHz.")
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gate-freq-khz
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max-khz))))
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(let ((start (get '*selection* 'start))
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(end (get '*selection* 'end)))
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(when (> (* *sound-srate* (- end start)) (1- (power 2 31)))
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;; Work around bug 2012 and 439.
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(throw 'err (format nil (_ "Error.
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Selection too long.
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Maximum length is ~a.") (format-time (/ (1- (power 2 31)) *sound-srate*))))))
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(when (< len 100) ;100 samples required
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;; Work around bug 2012.
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(throw 'err (format nil (_ "Error.
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Insufficient audio selected.
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Make the selection longer than ~a ms.")
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(round-up (/ 100000 *sound-srate*))))))
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;;; Analysis functions:
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;; Measure the peak level (dB) and suggest setting threshold a little higher.
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(defun analyze (sig)
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; Return analysis text.
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(let* ((test-length (truncate (min len (/ *sound-srate* 2.0))))
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(peakdb (peak-db sig test-length))
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(target (+ 1.0 peakdb))) ;suggest 1 dB above noise level
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;; Work around bug 2012.
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(format nil (_ "Peak based on first ~a seconds ~a dB~%
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Suggested Threshold Setting ~a dB.")
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(roundn (/ test-length *sound-srate*) 2)
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(roundn peakdb 2)
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(roundn target 0))))
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(defun peak-db (sig test-len)
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;; Return absolute peak (dB).
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;; For stereo tracks, return the maximum of the channels.
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(if (arrayp sig)
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(let ((peakL (peak (aref sig 0) test-len))
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(peakR (peak (aref sig 1) test-len)))
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(linear-to-db (max peakL peakR)))
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(linear-to-db test-len)))
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;;; Utility functions
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(defun round-up (num)
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(round (+ num 0.5)))
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(defun roundn (num places)
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;; Return number rounded to specified decimal places.
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(if (= places 0)
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(round num)
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(let* ((x (format NIL "~a" places))
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(ff (strcat "%#1." x "f")))
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(setq *float-format* ff)
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(format NIL "~a" num))))
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(defun format-time (s)
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;;; format time in seconds as h m.
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(let* ((hh (truncate (/ s 3600)))
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(mm (truncate (/ s 60))))
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;i18n-hint: hours and minutes. Do not translate "~a".
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(format nil (_ "~ah ~am") hh (- mm (* hh 60)))))
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;;; Gate Functions
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(defun noisegate (sig follow)
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;; Takes a sound and a 'follow' sound as arguments.
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;; Returns the gated audio.
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(let ((gain (/ (- 1 (* silence-flag floor)))) ; silence-flag is 0 or 1.
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(env (get-env follow)))
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(if (> gate-freq 20)
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(let* ((high (highpass8 sig gate-freq))
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(low (lowpass8 sig (* 0.91 gate-freq)))) ;magic number 0.91 improves crossover.
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(sim (mult high gain env) low))
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(mult sig gain env))))
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(defun get-env (follow)
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;; Return gate's envelope
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(let* ((gate-env (gate follow lookahead attack decay floor threshold))
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(gate-env (clip gate-env 1.0))) ;gain must not exceed unity.
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(diff gate-env (* silence-flag floor))))
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(defun peak-follower (sig)
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;; Return signal that gate will follow.
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(setf sig (multichan-expand #'snd-abs sig))
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(when (and (arrayp sig)(= stereo-link 0))
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(setf sig (s-max (aref sig 0) (aref sig 1))))
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(if (> hold 0)
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(multichan-expand #'snd-oneshot sig threshold hold)
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sig))
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(defun process ()
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(error-check)
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;; For stereo tracks, 'peak-follower' may return a sound
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;; or array of sounds, so pass it to 'noisegate' rather than
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;; calculating in 'noisegate'.
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(multichan-expand #' noisegate *track* (peak-follower *track*)))
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;; Run program
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(case mode
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(0 (catch 'err (process)))
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(T (analyze *track*)))
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