Fix Bug 2519 - Noise Gate fails silently on longer selections
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SteveDaulton
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@ -3,93 +3,114 @@ $version 4
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$type process
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$name (_ "Noise Gate")
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$manpage "Noise_Gate"
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$action (_ "Gating audio...")
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$debugbutton false
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$preview enabled
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$author (_ "Steve Daulton")
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$release 2.4.0
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$copyright (_ "Released under terms of the GNU General Public License version 2")
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;; Released under terms of the GNU General Public License version 2:
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$release 3.0.0
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$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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$control mode (_ "Select Function") choice ((_ "Gate")
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$control mode (_ "Select Function") choice (("Gate" (_ "Gate"))
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("Analyze" (_ "Analyse Noise Level")))
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0
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0
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$control stereo-link (_ "Stereo Linking") choice (("LinkStereo" (_ "Link Stereo Tracks"))
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("DoNotLink" (_ "Don't Link Stereo")))
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0
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$control low-cut (_ "Apply Low-Cut filter") choice ((_ "No")
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("10Hz" (_ "10Hz 6dB/octave"))
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("20Hz" (_ "20Hz 6dB/octave")))
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0
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;; Work around bug 2336.
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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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$control level-reduction (_ "Level reduction (dB)") float "" -12 -100 0
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$control threshold (_ "Gate threshold (dB)") float "" -48 -96 -6
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$control attack (_ "Attack/Decay (ms)") float "" 250 10 1000
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$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. Resample to around 1000 Hz (bug 2519).
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;; 2. If stereo track and stereo-link = 1, get the max of left and right.
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;; 3. TRIGGER 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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;; 4. 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, so
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;; that 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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;; 5. 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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(setq silence (if (> level-reduction -96) 0 1)) ; flag for silence
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(setq freq (* 1000.0 gate-freq))
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(setq level-reduction (db-to-linear level-reduction))
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(setq threshold (db-to-linear threshold))
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(setq attack (/ attack 1000.0))
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(setq look attack) ; lookahead
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(setq decay attack) ; this could be replaced with a slider if required
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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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;; As envelope is resampled to ~1000 Hz, the rise time will always be ~1 ms
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;; longer than specified attack, so compensate here.
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(setf attack (/ attack 1000.0))
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(setf lookahead attack)
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(setf attack (+ attack 0.001))
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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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(when (>= freq (* *sound-srate* 0.45)) ;10% below Nyquist should be safe maximum.
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;; Work around bug 2012.
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(throw 'err (format nil (_ "Error.
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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
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(roundn (* 0.00045 *sound-srate*) 1))))
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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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(when (< len 100) ;100 samples required
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;; Work around bug 2012.
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(throw 'err (format nil (_ "~%Insufficient audio selected.
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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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(levm (peak-avg-db sig test-length))
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(target (* 0.925 levm))) ;suggest 7.5% above noise level
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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 levm 2)
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(roundn peakdb 2)
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(roundn target 0))))
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(defun peak-avg-db (sig test-len)
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;; Return average of positive/ negative peaks (dB).
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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 ((avgL (peak-avg (aref sig 0) test-len))
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(avgR (peak-avg (aref sig 1) test-len)))
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(linear-to-db (max avgL avgR)))
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(let ((avg (peak-avg sig test-len)))
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(linear-to-db avg))))
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(defun peak-avg (sig test-len)
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;; Return average of positive/ negative peaks.
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;; We use the average for the analysis so as to ignore
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;; DC offet (assuming noise is approximately symetrical).
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(let* ((pos (s-max sig 0))
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(neg (s-min sig 0))
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(lev (peak pos test-len))
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(inv-lev (peak neg test-len)))
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(/ (+ lev inv-lev) 2.0)))
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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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(let ((peak (peak sig test-len)))
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(linear-to-db peak))))
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;;; Utility functions
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@ -109,48 +130,78 @@ Suggested Threshold Setting ~a dB.")
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;;; Gate Functions
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(defun noisegate (sig gatefollow lookahead risetime falltime floor threshold Hz)
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(let ((gain (/ (- 1 (* silence floor))))
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(env (get-env gatefollow lookahead risetime falltime floor threshold)))
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(if (> Hz 20)
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(sim (mult (highpass8 sig Hz) gain env)
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(lowpass8 sig (* 0.91 Hz))) ;magic number 0.91 improves crossover.
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(defun noisegate (sig follower)
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;; Takes a sound and a peak follower envelope (a low sample rate 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 follower)))
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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 look rise fall floor thresh)
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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 look rise fall floor thresh))
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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 floor))))
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(diff gate-env (* silence-flag floor))))
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(defun gate-follow (sig mode)
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(defun gate (sound lookahead risetime falltime floor threshold)
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;; This replaces Nyquist's GATE function. See bug 2519
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;; Note: this does NOT perform the actual gating, it just generates an exponential
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;; rise and decay for our "gain envelope".
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(setf sound (snd-gate (seq (cue sound) (stretch-abs 1.0 (s-rest lookahead)))
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lookahead risetime falltime floor threshold))
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(snd-xform sound (snd-srate sound) (snd-t0 sound)
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(+ (snd-t0 sound) lookahead) MAX-STOP-TIME 1.0))
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(defun peak-follower (sig) ;;FOLLOW
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;; Return signal that gate will follow.
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(setf sig (hp sig 20)) ; hp filter to remove DC off-set
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(if (and (= mode 0)(arrayp sig)) ; stereo track set to mono/link
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(s-max (s-abs (aref sig 0)) (s-abs (aref sig 1)))
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(s-abs sig)))
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;; Reduce sample rate to around 1000 Hz to allow
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;; longer tracks to be processed (bug 2519).
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(let ((step (round (/ *sound-srate* 1000))))
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(setf sig (multichan-expand #'snd-avg sig step step op-peak))
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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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; SND-AVG looks for peak in next 'step', so shift envelope one sample earlier.
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(setf sig (multichan-expand #'trim-first-sample sig))
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(if (> hold 0)
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(multichan-expand #'add-hold sig)
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sig)))
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(defun trim-first-sample (sig)
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;; Remove the first sample from sig.
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(let ((t0 (/ (snd-srate sig))))
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(extract-abs t0 MAX-STOP-TIME (cue sig))))
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(defun add-hold (sig)
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;; Extend 'above threshold peaks' by 'hold' seconds.
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;; TRIGGER acts when transitioning from less than or equal to zero to greater than zero,
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;; which is not ideal, but it's a lot faster than looping through samples with Lisp.
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;; We therefore need to invert the signal and offset vertically so that a fall across threshold
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;; becomes a rise above zero.
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(setf sig (mult -1 (diff sig threshold)))
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(let ((holding (trigger sig (cue (hold sig hold)))))
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(setf sig (sum threshold (mult -1 sig)))
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(sum sig holding)))
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(defun hold (sig dur)
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;; generate 'hold' sound.
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(control-srate-abs (snd-srate sig)
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(stretch-abs 1.0 (const 1.0 dur))))
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(defun hpfilter (sig)
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;; First order filters to minimise ringing.
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(case low-cut
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(1 (hp sig 10))
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(2 (hp sig 20))
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(T sig)))
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(defun process ()
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;; Main function
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(error-check)
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(let ((sig (hpfilter *track*)))
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(setf *track* nil)
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(setf gatefollow (gate-follow sig stereo-link))
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(multichan-expand #' noisegate sig
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gatefollow
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look
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attack
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decay
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level-reduction
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threshold
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freq)))
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;; 'peak-follower' may return a sound or array of sounds.
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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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