Substractive Synthesis and Filters
(definstrument onepole(start-time duration amplitude &key (b1 '(0 0.5 1 0.5))) (multiple-value-bind (beg end) (get-beg-end start-time duration) (let* ((noise (make-randh :frequency (* 0.49 sampling-rate) :amplitude amplitude)) (b1-env (make-env :envelope b1)) (opfilt (make-one-pole :a0 1.0 :b1 0.5))) (Run (loop for i from beg to end do (setf (smpflt-b1 opfilt) (env b1-env)) (outa i (one-pole opfilt (randh noise))))))))
(definstrument onezero(start-time duration amplitude &key (a1 '(0 0.5 1 0.5))) (multiple-value-bind (beg end) (get-beg-end start-time duration) (let* ((noise (make-randh :frequency (* 0.49 sampling-rate) :amplitude amplitude)) (a1-env (make-env :envelope a1)) (ozfilt (make-one-zero :a0 1.0 :a1 0.5))) (Run (loop for i from beg to end do (setf (smpflt-a1 ozfilt) (env a1-env)) (outa i (one-zero ozfilt (randh noise))))))))
(defmacro b1-from-r-freq (r freq) `(- (* 2.0 ,r (cos (in-hz ,freq))))) (defmacro b2-from-r (r) `(* ,r ,r)) (definstrument twopole(start-time duration amplitude &key (freq '(0 20 1 10000)) (r '(0 0.5 1 0.5))) (multiple-value-bind (beg end) (get-beg-end start-time duration) (let* ((noise (make-randh :frequency (* 0.49 sampling-rate) :amplitude amplitude)) (freq-env (make-env :envelope freq)) (r-env (make-env :envelope r)) (ppfilt (make-ppolar :r 0.5 :frequency 440.0))) (Run (loop for i from beg to end do (let* ((freq0 (env freq-env)) (r0 (env r-env))) (setf (smpflt-b1 ppfilt) (b1-from-r-freq r0 freq0)) (setf (smpflt-b2 ppfilt) (b2-from-r r0)) (outa i (ppolar ppfilt (randh noise)))))))))
(defmacro set-formnt(filter freq r) `(let* ((freq ,freq) (r ,r)) (setf (smpflt-a2 (frmnt-tz ,filter)) (- r) (smpflt-b1 (frmnt-tp ,filter)) (- (* 2.0 r (cos (in-hz freq)))) (smpflt-b2 (frmnt-tp ,filter)) (* r r)))) (definstrument simp-formnt(start-time duration amplitude &key (freq '(0 20 1 10000)) (r '(0 0.707 1 0.707))) (multiple-value-bind (beg end) (get-beg-end start-time duration) (let* ((noise (make-randh :frequency (* 0.5 sampling-rate) :amplitude amplitude)) (freq-env (make-env :envelope freq :start-time start-time :duration duration)) (r-env (make-env :envelope r :start-time start-time :duration duration)) (fmfilt (make-formnt :frequency 440 :r 0.99))) (Run (loop for i from beg to end do (set-formnt fmfilt (env freq-env) (env r-env)) (outa i (formnt fmfilt (randh noise))))))))All of these example instrument do some internal contortions to move through envelopes the center frequency, resonance and or assorted internal coefficients. Hope you can figure things out. Believe it or not everything that's being done is documented in the clm manual... :-)
In the first one we modified the code of the original v.ins (Bill's fm-violin) and added a moog filter based of Tim Stilson's moog filter. Needless to say, for this to work we have to first compile and load the moog filter code moog.ins. After that, compiling and loading the modified vmoog.ins fm violin file will generate a mutant fm-violin that understands two additional parameters, freq-env: the frequency envelope for the cutoff frequency of the moog filter and res-env: an envelope that controls the resonance of the filter.
We can also create a general purpose moog filter instrument that processes a soundfile. The code can be found in moog-filter.ins. One way to use this instrument to process arbitrary clm instrument output is to use a sound-let to create a temporary soundfile that holds the notes that are to be filtered. Better still, we can create a custom macro that adds some syntactic sugar and makes things look better. See the "with-moog" macro in the previous file plus an example on how to use it.
©1998 Fernando Lopez-Lezcano. All Rights Reserved. nando@ccrma.stanford.edu
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