Towards algorithmic orchestration (and customising sound playback with multiple sound libraries)

Dear Alain Jamot, 

here is a function that may help you. This function is useful for customising sound playback with multiple sound libraries or for algorithmic orchestration. 

The function expects an OMN expression and returns a list of multiple OMN sequences (multiple parts). It basically sorts notes from the OMN sequence into different parts, depending on the articulations of individual notes. All notes with certain articulations go in one resulting parts, and notes with other articulations in another part.

Here is an example. It sorts all notes with pizz or arco articulations into one part, and notes with trem articulations into another part. Each time, notes are substituted by rests in other parts, so that timing relations of notes in different parts are preserved.  

(separate-parts '((h c4 pizz q arco) (h trem q h pizz) (h arco+stacc -q fermata))
                '((pizz arco)
                  (trem)))
=> ; part 1: pizz and arco
   ((h c4 mf pizz q arco) (-h q c4 mf h pizz) (h c4 mf arco+stacc -q fermata))
   ; part 2: trem
   ((-h -q) (h c4 mf trem -q -h) (-h -q fermata)))

You can then assign your first part to on MIDI channel in your def-score call, and the next part to another MIDI channel, e.g., like so.

(setf omn-expr '((h c4 pizz q arco) (h trem q h pizz) (h arco+stacc -q fermata)))
(setf parts (separate-parts omn-expr
                            '((pizz arco)
                              (trem))))

(def-score two-violins
           (:title "Title"
            :composer "Composer"
            :copyright "Copyright © "
            :key-signature 'chromatic
            :time-signature '((1 1 1 1) 4)
            :tempo 100
            :layout (bracket-group
                     (violin1-layout 'violin1)
                     (violin2-layout 'violin2)))
  
  (violin1
   :omn (nth 0 parts)
   :channel 1
   :sound 'gm
   :program 'violin
   :volume 100
   :pan 54
   :controllers (91 '(48))
   )
  
  (violin2
   :omn (nth 1 parts)
   :channel 2
   :sound 'gm
   :program 'violin
   :volume 100
   :pan 74
   :controllers (91 '(60))
   )
  )

The function definition of separate-parts is below.

Best,

Torsten

Janusz: This is another example of a function showing how processing polyphonic music with double-nested OMN expressions can be useful. Once we have a standard notation for polyphonic OMN expressions with multiple voices/parts in Opusmodus 2, as discussed earlier, then this function can easily be adapted to output that format. 

(labels ((make-corresponding-rest (event)
         (let ((len (omn-encode (first event))))
           (cons 
            ;; rests should remain rests
            (if (> len 0)
              (* len -1)
              len)
            (omn :rest-articulation event))))
       (push-event-and-rests (event matching-position result-omns articulation-sets-length)
         (push event (nth matching-position result-omns))
         (loop for i in (remove matching-position (gen-integer 0 (1- articulation-sets-length)))
           do (push (make-corresponding-rest event) (nth i result-omns)))))
  (defun separate-parts (sequence articulation-sets)
    "The function `separate-parts' is useful for customising your sound playback with multiple sound libraries or for algorithmic orchestration. 
    The function breaks an OMN sequence (a single part) into a list of multiple OMN sequences (multiple parts). It basically sorts notes from the OMN sequence into different parts, depending on the articulations of individual notes. All notes with certain articulations go in one resulting parts, and notes with other articulations in another part. In all other resulting parts, notes are substituted by rests, so that timing relations of notes in different parts are preserved. 
    This function can be useful, when you have multiple sound libraries that support different articulations of the same instrument. You can then perform notes with certain articulations on one software instrument (on its own MIDI channel etc.), and notes with other articulations on another instrument. 
    Alternatively, you can use the function for algorithmic orchestration, where you assign custom articulations (typically declared with add-text-attributes first) such as instrument labels with your custom algorithm, and then use this function in a second step to separate your instruments.

    Remember that the result of this function is a list of multiple OMN sequences (multiple parts). You have to split it into its individual parts for use in OMN. 

    Args:
    - sequence: OMN sequence, can be nested
    - articulation-sets: list of list of articulations. All notes with articulations contained in the first articulation-set end up in the first resulting part, notes with articulations in the second set end up in the second part and so forth. 
    
    The decision which part a note belongs to is always made based on the first articulation that matches an articulation-set. If a note contains no articulation, or an articulation contained in no set, then it is matched to the first articulation-set. If an articulation is contained in multiple articulation-sets, then the earlier match in articulation-sets is used.

    Examples: 
    
(separate-parts '(h c4 pizz q arco)
                '((pizz)
                  (arco)))
=> ((h c4 mf pizz -q)   ; part 1 with pizz articulations
    (-h q c4 mf arco))  ; part 2 with arco

(separate-parts '((h c4 pizz q arco) (h trem q h pizz) (h arco+stacc -q fermata))
                '((pizz arco)
                  (trem)))
=> (((h c4 mf pizz q arco) (-h q c4 mf h pizz) (h c4 mf arco+stacc -q fermata)) ; part 1: pizz and arco
    ((-h -q) (h c4 mf trem -q -h) (-h -q fermata)))                             ; part 2: trem
"
    (if (listp (first sequence))
      ;; sequence is nested
      (matrix-transpose 
       (mapcar #'(lambda (seq) (separate-parts seq articulation-sets))
               sequence))
      ;; sequence is flat list
      (let* ((articulation-sets-length (length articulation-sets))
             (result-omns (make-list articulation-sets-length :initial-element nil)))
        (loop for event in  (single-events sequence) 
          do (let ((event-articulation (fourth event)))
               (if event-articulation
                 (let ((matching-position
                        (position-if #'(lambda (articulation-set)
                                         (some #'(lambda (art) 
                                                   (member art (disassemble-articulations event-articulation)))
                                               articulation-set))
                                     articulation-sets)))
                   (if matching-position
                     (push-event-and-rests event matching-position result-omns articulation-sets-length)
                     ;; if no match, then add event to first omn result                    
                     (push-event-and-rests event 0 result-omns articulation-sets-length)))
                 ;; if no articulation, then add event to first omn result 
                 (push-event-and-rests event 0 result-omns articulation-sets-length))))
        (mapcar #'(lambda (result) (flatten-omn (reverse result))) result-omns)))))
        
;; for  your convenience, I include the following definition already shared earlier
(defun disassemble-articulations (art)
  "Splits a combined OMN articulations into a list of its individual attributes.

  Example:
  (disassemble-articulations 'leg+ponte)
  => (leg ponte)"  
  (mapcar #'intern (split-string (symbol-name art) :separator "+")))