• # Lesson 21. Mapping, Substituting and Interleaving

## Annotation

The score-script of this piece begins with a function. It does the same thing as GEN-CHORD, but it is very simplified and at this stage a little easier to explain and use. It's also an example of how a composer with a little knowledge of LISP can write his/her own functions. This function only uses LISP primitives, that is words that are available to everyone using Opusmodus.

### Section A

The objective with Lesson 21 is to compose a piece using chords derived from pitches. To see how this is done let's take apart the expression called chord-sequence:

(setf chord-seqeunce
(sort-asc ;3
(gen-bundle (rnd-sum 10 '(2 3) :seed 22 ) ;2
(rnd-order (flatten p-transp) ;1
:seed 56))))

Here's the output of the line marked ;1

=> (g4 cs5 gs4 cs5 d5 fs5 cs4 g4 gs4 cs4 c5 c6 c5
c4 fs4 d4 g5 fs4 cs5 g4 cs5 g5 g4 fs5 c5)

We've randomised the order of p-tranpose.

Now evaluate the lines marked ;2 and ;1:

(gen-bundle (rnd-sum 10 '(2 3) :seed 22)
(rnd-order (flatten p-transp) :seed 56))
=> (g4cs5gs4 cs5d5fs5 cs4g4 gs4cs4
c5c6c5 c4fs4d4 g5fs4 cs5g4 cs5g5g4 fs5c5))

Now we can see what GEN-BUNDLE does. It creates chords of 2 or 3 pitches:

(sort-asc
(gen-bundle (rnd-sum 10 '(2 3) :seed 22)
(rnd-order (flatten p-transp) :seed 56)))

Finally, adding SORT-ASC makes a rising progression for this chord-sequence. To help the next step the output has been placed on the score-script itself and numbered one to ten:

(setf chd-order '(7 8 4 10 4 3 9 3 6 2 6 2 7 8 10 4))
(setf chd-play (substitute-map
chord-seqeunce
(gen-integer 1 12) chd-order))

The function SUBSTITUTE-MAP enables the composer to write a progression of chords with chd-order and then substitute that list for chord-sequence:

=> (g4cs5g5 c5c5c6 fs4g5 cs5d5fs5 fs4g5 cs4gs4 . . .)

Once the new progression is in place the rest of the composition of Section A follows the usual pattern except for the next expression chd-lengths.

We saw in Lesson 20 the value of the LISP primitive LENGTH. With GET-COUNT we can see how many chords tones we have in each chord because we want the left hand of the piano to play melodically:

(pitch-melodize (mclist chd-play))
=> ((g4 cs5 g5) (c5 c5 c6) (fs4 g5) (cs5 d5 fs5) . . .))

So we map with GET-COUNT to find out the length of each list.

(setf chd-lengths
(get-count
(pitch-melodize (mclist chd-play))))
=> (3 3 2 3 2 2 2 2 2 2 2 2 3 3 3 2)

And with this string of numbers we can make the bass-play variable and get the list/bar length to create the correct metre grouping.

### Section B

This section uses the INTERLEAVE-MAP function to move the melody and chords between both hands. For an easy example of how it works look up INTERLEAVE-MAP in the documents.

(setf
i-1 '(1 2 1 2)
i-2 '(2 1)

p-1 '(c4 cs4 fs4 g4 c5)
p-2 '(c5 b4 fs4 f4 c4)
)
(interleave-map (list i-1 i-2) (list p-1 p-2))
=> (c4 c5 b4 cs4 fs4 fs4 g4 f4 c4 c5)

;(c4       cs4 fs4     g4       c5)
;(   c5 b4         fs4    f4 c4   )

Now here’s INTERLEAVE-MAP being used in Section B:

(setf i-map
(interleave-map
(list i-1 i-2)
(list (span rhy chd-play)
(pitch-transpose 12 bass-play)))))

Now to use AMBITUS in the interleaved part for the right hand. This moves the melodic pitches of bass-play up into the treble clef:

(setf i-rh (ambitus '(g4 c6) i-map))
=> ((g3 cs3 g3) (g3cs3g3 c4c4c4 fs3g3)
(cs3d3fs3 fs3g3 cs3gs3) (c3 c3 c3) . . .))

When we come to do the same for the left hand we’ll put AMBITUS together with INTERLEAVE-MAP.

(setf j-map
(interleave-map
(list i-1 i-2)
(list bass-play (span rhy chd-play))))

In the expressions for dynamics see how the final dynamic in the list is replaced using POSITION-REPLACE by a triple forte! Remember when counting sections 0 is the starting point. Hence this expression:

(position-replace (- (length chd-order) 1) '((fff)) . . .)
(- (length chd-order) 1)
=> 15

## Score

;; Function
(defun gen-bundle (n-bundle pitch-list)
(mapcar (function (lambda (x) (compress x)))
(gen-divide n-bundle pitch-list)))

;; Section A
(setf pitches '(c4 cs4 fs4 g4 c5))
(setf p-transp
(pitch-transpose
(pitch-to-integer pitches)
(gen-repeat 5 (list pitches))))

(setf chord-sequence
(respell (sort-asc
(gen-bundle
(rnd-sum 10 '(2 3) :seed 22)
(rnd-order (flatten p-transp) :seed 561)))))

;(c4d4fs4 cs4g4 cs4gs4 fs4g5 g4ab4cs5
; 1       2     3      4     5
; g4cs5 g4cs5g5 c5c5c6 c5fs5 cs5d5fs5)
; 6     7       8      9     10

(setf chd-order '(7 8 4 10 4 3 9 3 6 2 6 2 7 8 10 4))
(setf chd-play (substitute-map
chord-sequence
(gen-integer 1 10) chd-order))

(setf chd-lengths (get-count (pitch-melodize (mclist chd-play))))
(setf bass-play (ambitus
'(c2 g3)
(gen-divide chd-lengths
(pitch-transpose
-12 (pitch-melodize chd-play)))))

(setf rhy (span bass-play '(e)))
(setf rhy-c (get-span rhy))
(setq rh-1 (make-omn
:length rhy-c
:pitch (span rhy chd-play)
:velocity '(mp)))

(setq lh-1 (make-omn
:length (length-weight rhy :weight '(4 1) :seed 231)
:pitch bass-play
:velocity '(f)))

;; Section B
(setf i-1 '(1 2 1 2))
(setf i-2 '(2 1))
(setf i-map
(interleave-map
(list i-1 i-2)
(list (span rhy chd-play)
(pitch-transpose 12 bass-play))))

(setf i-rh (ambitus '(g4 c6) i-map))
(setf j-map
(interleave-map
(list i-1 i-2)
(list bass-play (span rhy chd-play))))

(setf i-lh (ambitus '(g2 c4) j-map))
(setf i-dyn-k (span rhy (interleave-map
(list i-1 i-2)
(list (span  bass-play '(ff))
(span rhy '(p))))))

(setf i-dyn-l (position-replace
(- (length chd-order) 1)
'((fff)) i-dyn-k :type 'list))

(setq rh-2 (make-omn
:length (length-weight rhy :weight '(4 1) :seed 231)
:pitch i-rh
:velocity i-dyn-l))

(setq lh-2 (make-omn
:length rhy
:pitch i-lh
:velocity i-dyn-l))

(setq rh-AB (chord-pitch-unique (assemble-seq rh-1 rh-2)))
(setq lh-AB (chord-pitch-unique (assemble-seq lh-1 lh-2)))
(setf timesigs (get-time-signature lh-AB))

(def-score lesson-21
(:key-signature 'chromatic
:time-signature timesigs
:tempo 80
:layout (piano-layout 'piano-rh 'piano-lh))

(piano-rh
:omn rh-AB
:channel 1
:sound 'gm
:program 'acoustic-grand-piano)

(piano-lh
:omn lh-AB)
)

## Notation

Next page Lesson 22. Lengths and Rhythms

Go back to Reference page.

Edited by opmo

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