:orphan:

Performance Post-Processing
===========================

*Example script* (scamp): `examples/Notation & engraving/Special notations/post_processing.py <https://github.com/MarcTheSpark/scamp/blob/main/examples/Notation%20%26%20engraving/Special%20notations/post_processing.py>`__

*Download:* :download:`post_processing.py <downloads/notation_engraving_special_notations_post_processing/post_processing.py>`

Post-processes a recorded Performance of a random walk of thirds and fifths, so that every time three consecutive notes are a triad, they are slurred together and spelled consistently.

*Topics:* :doc:`Notation & engraving › Special notations <notation_engraving>`

.. raw:: html

   <div style="border:1px solid #ccc;padding:8px;margin:0.2em 0 0.6em;display:inline-block;max-width:100%"><img src="../_static/media/Notation%20%26%20engraving/Special%20notations/post_processing.svg" alt="score" style="max-width:100%;height:auto;display:block"></div>

.. raw:: html

   <div style="margin:0.6em 0"><audio controls preload="none" src="../_static/media/Notation%20%26%20engraving/Special%20notations/post_processing.mp3" style="width:100%;max-width:520px"></audio></div>

.. code-block:: python

   from scamp import *
   import random

   random.seed(38)  # makes output deterministic

   s = Session()
   s.tempo = 120

   violin = s.new_part("violin")

   s.start_transcribing()

   pitch = 70
   while s.beat < 40:
       dur = random.choice([0.5, 1.0])
       violin.play_note(pitch, 0.5, dur)
       # go up or down by a 5th, 4th, or major or minor 3rd
       pitch += random.choice([-7, -5, -4, -3, 3, 4, 5, 7])
       if pitch < 55:
           pitch += 12
       elif pitch > 93:
           pitch -= 12

   perf = s.stop_transcribing()


   # ----------------- POST PROCESSING --------------------#

   triads = {
       'major': [{n, (n + 4) % 12, (n + 7) % 12} for n in range(12)],
       'minor': [{n, (n + 3) % 12, (n + 7) % 12} for n in range(12)]
   }

   triad_spellings = {
       'major': [SpellingPolicy.all_flats() if n in (1, 3, 8, 10) else SpellingPolicy.all_sharps() for n in range(12)],
       'minor': [SpellingPolicy.all_flats() if n in (0, 3, 5, 7, 10) else SpellingPolicy.all_sharps() for n in range(12)]
   }

   def get_triad(pcs):
       """Determines which (if any) major or minor triad these pitch classes belong to."""
       pcs_set = set(pcs)
       if pcs_set in triads['major']:
           return 'major', triads['major'].index(pcs_set)
       elif pcs_set in triads['minor']:
           return 'minor', triads['minor'].index(pcs_set)
       return False


   last_pitch_classes = []
   last_notes = []

   for note in perf.parts[0].get_note_iterator():
       last_notes.append(note)
       last_pitch_classes.append(note.pitch % 12)
       # only keep the last 3 pitch classes
       if len(last_notes) > 3:
           last_notes.pop(0)
           last_pitch_classes.pop(0)

       # check for a triad and process
       if len(last_pitch_classes) == 3 and (triad := get_triad(last_pitch_classes)):
           last_notes[0].properties.spanners.append(StartSlur())
           last_notes[-1].properties.spanners.append(StopSlur())

           major_minor, root = triad
           for note in last_notes:
               note.properties.spelling_policies = [triad_spellings[major_minor][root]]

           # clear the notes list so that we start fresh with the next note
           last_notes.clear()
           last_pitch_classes.clear()

   perf.to_score().show()