Lecture Slides

Modulation Synthesis

Ring Modulation

(definstrument rm (start-time duration carrier-freq modulator-freq amplitude
		   &key
		   (amp-env '(0 0 0.5 1 1 0)))
  (let* ((beg (floor (* start-time *srate*)))
	 (end (+ beg (floor (* duration *srate*))))
	 (carrier (make-oscil :frequency carrier-freq))
	 (modulator (make-oscil :frequency modulator-freq))
	 (envelope (make-env :envelope amp-env 
			     :scaler amplitude
			     :duration duration)))
    (run
     (loop for i from beg to end do
       (outa i (* (env envelope)
		  (* (oscil carrier)(oscil modulator))))))))

(definstrument rmw (start-time duration carrier-freq modulator-freq amplitude
		   &key
		   (carrier-spectr '(1 0.5 2 0.2 5 0.1))
		   (modulator-spectr '(1 0.5 3 0.2 4 0.1))
		   (amp-env '(0 0 0.5 1 1 0)))
  (let* ((beg (floor (* start-time *srate*)))
	 (end (+ beg (floor (* duration *srate*))))
	 (wave-c (partials->wave carrier-spectr))
	 (carrier (make-table-lookup :frequency carrier-freq :wave wave-c))
	 (wave-m (partials->wave modulator-spectr))
	 (modulator (make-table-lookup :frequency modulator-freq :wave wave-m))
	 (envelope (make-env :envelope amp-env 
			     :scaler amplitude
			     :duration duration)))
    (run
    (loop for i from beg to end do
      (outa i (* (env envelope)
		 (* (table-lookup carrier)(table-lookup modulator))))))))

Amplitude Modulation

(definstrument am (start-time duration carrier-freq modulator-freq amplitude
		   &key
		   (amp-env '(0 0 0.5 1 1 0)))
  (let* ((beg (floor (* start-time *srate*)))
	 (end (+ beg (floor (* duration *srate*))))
	 (carrier (make-oscil :frequency carrier-freq))
	 (modulator (make-oscil :frequency modulator-freq))
	 (envelope (make-env :envelope amp-env 
			     :scaler amplitude
			     :duration duration)))
    (run
    (loop for i from beg to end do
      (outa i (* (env envelope)
		 (* (oscil carrier)(+ 1.0 (oscil modulator)))))))))

Frequency Modulation

(definstrument fm (start-time duration carrier-freq modulator-freq index amplitude
		   &key
		   (amp-env '(0 0 0.5 1 1 0)))
  (let* ((beg (floor (* start-time *srate*)))
	 (end (+ beg (floor (* duration *srate*))))
	 (carrier (make-oscil :frequency carrier-freq))
	 (modulator (make-oscil :frequency modulator-freq))
	 (envelope (make-env :envelope amp-env 
			     :scaler amplitude
			     :duration duration)))
    (run
     (loop for i from beg to end do
       (outa i (* (env envelope)
		  (oscil carrier (* index (oscil modulator))))))))))