:orphan:

Voice Leading / spelling policy
===============================

*Example script* (scamp_extensions): `examples/Pitch/Pitch spelling/voice_leading.py <https://github.com/MarcTheSpark/scamp_extensions/blob/main/examples/Pitch/Pitch%20spelling/voice_leading.py>`__

*Download:* :download:`voice_leading.py <downloads/pitch_pitch_spelling_voice_leading/voice_leading.py>`

**Requires the** ``scamp_extensions`` **package** (``pip install scamp_extensions``).

Rule-based four-part voice leading over a scale, spelled in E major via the `default_spelling_policy` argument.

*Topics:* :doc:`Time & clocks › Forking & simultaneity <time_clocks>`, :doc:`Pitch › Pitch spelling <pitch>`

.. 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/Pitch/Pitch%20spelling/voice_leading.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/Pitch/Pitch%20spelling/voice_leading.mp3" style="width:100%;max-width:520px"></audio></div>

.. code-block:: python

   from scamp import *
   from scamp_extensions.pitch import Scale

   s = Session()

   piano_treb = s.new_part("piano", clef_preference="treble", default_spelling_policy="E major")
   piano_bass = s.new_part("piano", clef_preference="bass", default_spelling_policy="E major")

   scl = Scale.major(64)

   bass_line = [-7, -6, -5, -9, -10, -12, -13, -10, -14]

   upper_parts = [-3, 0, 2]

   last_bass_degree = None

   def check_chord_tone(interval_with_bass):
       return interval_with_bass % 7 in (0, 2, 4)

   def move_upper_parts(old_bass_note, new_bass_note):
       bass_motion = new_bass_note - old_bass_note
       bass_motion_mod = bass_motion % 7

       if bass_motion_mod == 0:
           return
       elif bass_motion_mod in [1, 6]:
           # stepwise motion
           # move to nearest consonance in opposite motion to bass
           direction_to_move = -1 if bass_motion > 0 else 1
       elif bass_motion_mod in [2, 4]:
           direction_to_move = -1
       else:
           direction_to_move = 1
           
       for i, p in enumerate(upper_parts):
           while not check_chord_tone(p - new_bass_note):
               p += direction_to_move
           upper_parts[i] = p

   s.start_transcribing()
   for bass_degree in bass_line:
       if last_bass_degree is not None:
           move_upper_parts(last_bass_degree, bass_degree)
       last_bass_degree = bass_degree
       piano_bass.play_note(scl.degree_to_pitch(bass_degree), 1, 1, blocking=False)
       piano_treb.play_chord(scl.degree_to_pitch(upper_parts), 1, 1)

   scl.transpose(4)

   for bass_degree in bass_line:
       if last_bass_degree is not None:
           move_upper_parts(last_bass_degree, bass_degree)
       last_bass_degree = bass_degree
       piano_bass.play_note(scl.degree_to_pitch(bass_degree), 1, 1, "spelling: Ab major", blocking=False)
       piano_treb.play_chord(scl.degree_to_pitch(upper_parts), 1, 1, "spelling: Ab major")

   s.stop_transcribing().to_score().show()