pentatonic scale

[A.G. Hamill]

Hello group,

A quick question: Is it true that Music21 has no built-in method for constructing a pentatonic scale given a starting pitch (like it does for other scales major, minor, octatonic, etc.)?

I searched the documentation on the word "pentatonic" and only got two results, both were a dead-ends for me.

Thanks much,

Anne

[Georges Dimitrov]

Hi,

This is something I noted too, and I created custom classes for it:

import music21

from music21.scale import intervalNetwork

class AbstractPentatonicScale(music21.scale.AbstractScale):

    def __init__(self, mode=None):

        super().__init__()

        self.type = "Abstract Pentatonic"

        # all pentatonic scales are octave duplicating

        self.octaveDuplicating = True

        # here, accept None

        self.buildNetwork(mode=mode)

    def buildNetwork(self, mode=None):

        src_list = ("M2", "M2", "m3", "M2", "m3")

        if mode in (None, 1, "major", "Major"):

            interval_list = src_list

            self.tonicDegree = 1

        elif mode == 2:

            interval_list = src_list[1:] + src_list[:1]

            self.tonicDegree = 1

        elif mode == 3:

            interval_list = src_list[2:] + src_list[:2]

            self.tonicDegree = 1

        elif mode == 4:

            interval_list = src_list[3:] + src_list[:3]

            self.tonicDegree = 1

        elif mode in (5, "minor", "Minor"):

            interval_list = src_list[4:] + src_list[:4]

            self.tonicDegree = 1

        else:

            raise music21.scale.ScaleException(

                f"cannot create a scale of the following mode: {mode}"

            )

        self._net = intervalNetwork.IntervalNetwork(

            interval_list,

            octaveDuplicating=self.octaveDuplicating,

            pitchSimplification="none",

        )

        # might also set weights for tonic and dominant here

class PentatonicScale(music21.scale.ConcreteScale):

    usePitchDegreeCache = True

    def __init__(self, tonic=None, mode=None):

        super().__init__(tonic=tonic)

        self._abstract = AbstractPentatonicScale(mode=mode)

        self.type = "Pentatonic"

I made these for my procedural composition library (https://github.com/georgesdimitrov/arvo) which I started developing in 2021, and unfortunately didn’t have much time to maintain, but I’ve been progressively working on a major update which I should publish this week! The update will add a lot of functionality (such as those extra scales), and compatibility with music21 v9.

Georges Dimitrov

georges....@gmail.com

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