Lesson 9. The Bass Part

Annotation

Two new functions enable the left-hand bass part to play sustained pitches for the length of each bar. This is a very common requirement in a multi-part texture where metres may be constantly changing.

The first new function is GET-SPAN. This adds up each list of lengths.

(setf rhythm (span line-rnd '(e)))
=> ((1/8 1/8 1/8 1/8) (1/8 1/8 1/8 1/8)
    (1/8 1/8 1/8 1/8 1/8) (1/8 1/8 1/8 1/8) (1/8 1/8 1/8))

(setf bass-rhythm (get-span rhythm))
=> (1/2 1/2 5/8 1/2 3/8)

The second function is FILTER-FIRST. This function selects the first pitch of each list in bass-line and groups them together as a separate list bass-select.

(setf bass-line (span line-rnd bass))
=> ((c2 cs2 fs2 g2) (c3 c2 cs2 fs2)
    (g2 c3 c2 cs2 fs2) (g2 c3 c2 cs2) (fs2 g2 c3))

(setf bass-select (filter-first 1 bass-line))
=> ((c2) (c3) (g2) (g2) (fs2))

Score

(setf line '(c4 cs4 fs4 g4 c5))
(setf bass (pitch-transpose -24 line))
(setf chords '(c4cs4fs4 g4c5))
(setf line-rnd (gen-eval 5 '(rnd-sample (rnd-range 3 5) line) :seed 41))
(setf rhythm (span line-rnd '(e)))
(setf bass-line (span line-rnd bass))
(setf dynamics (mclist '(f p f p ff)))
(setf dyn-spanned (span line-rnd dynamics))
(setf bass-rhythm (get-span rhythm))
(setf bass-select (filter-first 1 bass-line))

(setf line-1 (make-omn 
              :length rhythm
              :pitch line-rnd
              :velocity dyn-spanned))

(setf bass-1 (make-omn 
              :length bass-rhythm
              :pitch bass-select
              :velocity dyn-spanned))

(setf ts-list (get-time-signature line-1))

(def-score lesson-9
           (:key-signature 'chromatic
            :time-signature ts-list
            :tempo 100
            :layout (piano-layout 'piano-rh 'piano-lh))
  
  (piano-rh    
   :omn line-1
   :channel 1
   :sound 'gm
   :program 'acoustic-grand-piano)  
  
  (piano-lh    
   :omn bass-1)
   )

Notation

Next page Lesson 10. Gesture

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