Locate and position the current Audacity source code, and clear a variety of old junk out of the way into junk-branches

plug-ins/lowpass.ny

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+;nyquist plug-in
+;version 3
+;type process
+;categories "http://lv2plug.in/ns/lv2core#LowpassPlugin"
+;name "Low Pass Filter..."
+;action "Performing Low Pass Filter..."
+;info "by Dominic Mazzoni, modified by David R. Sky\nReleased under terms of the GNU General Public License Version 2\nAttenuates high frequencies above your specified cutoff frequency.\nHigher rolloff values give a sharper attenuation of frequencies above\nthe cutoff frequency. If using a rolloff of 12 dB, a [q] value greater than\ndefault 0.7 increases resonance ['ringing'] of the cutoff frequency and\ncould result in clipping.""
+
+;control rolloff-choice "     Rolloff [dB per octave]" choice "  6 dB,12 dB,24 dB,36 dB,48 dB" 0
+;control q "     Filter quality [q] for 12 dB rolloff" real "" 0.7071 .1 20
+;control f "     Cutoff frequency [Hz]" real "" 1000 1 20000
+
+; note that all Nyquist lowpass functions 
+; [lp, lowpass2, lowpass4, lowpass6, lowpass8]
+; are defined below with -s suffix.
+; This enables lowpass functions other than lp 
+; to deal with stereo selection,
+; and dummy q arg for all but lowpass2 
+
+; 6dB/octave
+(defun lp-s (s f q) ; dummy q arg
+(lp s f))
+
+; 12dB/octave
+(defun lowpass2-s (s f q)
+(if (arrayp s)
+(vector (lowpass2 (aref s 0) f q)
+(lowpass2 (aref s 1) f q))
+(lowpass2 s f q)))
+
+; 24dB/octave
+(defun lowpass4-s (s f q) ; dummy q arg
+(if (arrayp s)
+(vector (lowpass4 (aref s 0) f)
+(lowpass4 (aref s 1) f))
+(lowpass4 s f)))
+
+; 36dB/octave
+(defun lowpass6-s (s f q) ; dummy q arg
+(if (arrayp s)
+(vector (lowpass6 (aref s 0) f)
+(lowpass6 (aref s 1) f))
+(lowpass6 s f)))
+
+; 48dB/octave
+(defun lowpass8-s (s f q) ; dummy q arg
+(if (arrayp s)
+(vector (lowpass8 (aref s 0) f)
+(lowpass8 (aref s 1) f))
+(lowpass8 s f)))
+
+; check function: returns 1 on error
+(defun check (arg min max)
+(if (and (>= arg min) (<= arg max))
+0 1))
+
+
+; initialize blank error-msg
+(setf error-msg "")
+
+; check for erroneous q value
+(setf error-msg (if 
+(and (= rolloff-choice 1)
+(= (check q 0.1 20) 1))
+(strcat error-msg (format nil
+"q value ~a lies outside valid range 0.1 to 20     
+for your chosen rolloff of 12 dB per octave.
+" q))
+error-msg))
+
+; check for erroneous frequency cutoff value
+(setf error-msg (if 
+(= (check f 1 20000) 0)
+error-msg
+(strcat error-msg (format nil
+"Cutoff frequency ~a Hz lies outside valid range 1 to 20000.     
+" f))))
+
+
+(cond
+((> (length error-msg) 0)
+(setf error-msg (strcat (format nil
+"Error - \n\nYou have entered at least one invalid value:
+") error-msg))
+(format nil "~a" error-msg)) 
+;
+(t ; perform lowpass effect
+(funcall (nth rolloff-choice '(lp-s lowpass2-s lowpass4-s lowpass6-s lowpass8-s)) 
+s f q)))
+
+; from previous commit
+; arch-tag: c2d96e46-b4e2-47c0-9a19-761011418e02
+