aiexperiments-ai-duet/server/magenta/music/chord_symbols_lib.py

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2016-11-11 18:53:51 +00:00
# Copyright 2016 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Utility functions for working with chord symbols."""
import abc
import music21
import tensorflow as tf
# chord quality enum
CHORD_QUALITY_MAJOR = 0
CHORD_QUALITY_MINOR = 1
CHORD_QUALITY_AUGMENTED = 2
CHORD_QUALITY_DIMINISHED = 3
CHORD_QUALITY_OTHER = 4
class ChordSymbolException(Exception):
pass
class ChordSymbolFunctions(object):
"""An abstract class for interpreting chord symbol strings.
This abstract class is an interface specifying several functions for the
interpretation of chord symbol strings:
`transpose_chord_symbol` transposes a chord symbol a given number of steps.
`chord_symbol_midi_pitches` returns a list of MIDI pitches in a chord.
`chord_symbol_root` returns the root pitch class of a chord.
`chord_symbol_quality` returns the "quality" of a chord.
"""
__metaclass__ = abc.ABCMeta
@staticmethod
def get():
"""Returns the default implementation of ChordSymbolFunctions.
Currently the default (and only) implementation of ChordSymbolFunctions is
Music21ChordSymbolFunctions.
Returns:
A ChordSymbolFunctions object.
"""
return Music21ChordSymbolFunctions()
@abc.abstractmethod
def transpose_chord_symbol(self, figure, transpose_amount):
"""Transposes a chord symbol figure string by the given amount.
Args:
figure: The chord symbol figure string to transpose.
transpose_amount: The integer number of half steps to transpose.
Returns:
The transposed chord symbol figure string.
Raises:
ChordSymbolException: If the given chord symbol cannot be interpreted.
"""
pass
@abc.abstractmethod
def chord_symbol_midi_pitches(self, figure):
"""Return the pitches of a chord as MIDI note values.
Args:
figure: The chord symbol figure string for which pitches are computed.
Returns:
A python list of pitches as integer MIDI note values.
Raises:
ChordSymbolException: If the given chord symbol cannot be interpreted.
"""
pass
@abc.abstractmethod
def chord_symbol_root(self, figure):
"""Return the root pitch class of a chord.
Args:
figure: The chord symbol figure string for which pitches are computed.
Returns:
The pitch class of the chord root, an integer between 0 and 11 inclusive.
Raises:
ChordSymbolException: If the given chord symbol cannot be interpreted.
"""
pass
@abc.abstractmethod
def chord_symbol_quality(self, figure):
"""Return the quality (major, minor, dimished, augmented) of a chord.
Args:
figure: The chord symbol figure string for which quality is computed.
Returns:
One of CHORD_QUALITY_MAJOR, CHORD_QUALITY_MINOR, CHORD_QUALITY_AUGMENTED,
CHORD_QUALITY_DIMINISHED, or CHORD_QUALITY_UNKNOWN.
Raises:
ChordSymbolException: If the given chord symbol cannot be interpreted.
"""
pass
class Music21ChordSymbolFunctions(ChordSymbolFunctions):
"""A class that uses music21 to interpret chord symbol strings."""
# music21 returns this ugly string when it can't parse a chord.
_MUSIC21_UNIDENTIFIED_CHORD = 'Chord Symbol Cannot Be Identified'
# Mapping from strings returned by music21 to chord quality enum values.
_music21_chord_quality_mapping = {
'major': CHORD_QUALITY_MAJOR,
'minor': CHORD_QUALITY_MINOR,
'augmented': CHORD_QUALITY_AUGMENTED,
'diminished': CHORD_QUALITY_DIMINISHED
}
def __init__(self):
"""Construct a Music21ChordSymbolFunctions object."""
self._music21_chord_symbol_dict = {}
def _to_music21_chord_symbol(self, figure):
"""Return a music21.harmony.ChordSymbol object instantiated with `figure`.
Since this operation can be slow and chord symbols are often repeated many
times in a single score, we also memoize the mapping.
Args:
figure: The chord symbol figure string.
Returns:
A music21.harmony.ChordSymbol object.
Raises:
ChordSymbolException: If the chord fails to be parsed by music21.
"""
if figure in self._music21_chord_symbol_dict:
return self._music21_chord_symbol_dict[figure]
try:
cs = music21.harmony.ChordSymbol(figure)
self._music21_chord_symbol_dict[figure] = cs
return cs
except: # pylint: disable=bare-except
pass
try:
# music21 seems to have a hard time parsing some chord symbol figure
# strings it itself produces! It sometimes produces strings like
# "C7 add b9" or "G7 alter #5", and then can't re-parse them. In these
# cases, let's try again with just the basic chord.
cs = music21.harmony.ChordSymbol(figure.split()[0])
self._music21_chord_symbol_dict[figure] = cs
tf.logging.warn('Failed to parse chord symbol %s, '
'interpreting as %s', figure, figure.split()[0])
return cs
except:
raise ChordSymbolException('unable to parse chord symbol: %s'
% figure)
def transpose_chord_symbol(self, figure, transpose_amount):
chord_symbol = self._to_music21_chord_symbol(figure)
transposed_figure = chord_symbol.transpose(transpose_amount).findFigure()
if transposed_figure == self._MUSIC21_UNIDENTIFIED_CHORD:
# music21 just returns error text instead of throwing.
raise ChordSymbolException('unable to parse chord symbol: %s'
% figure)
else:
return transposed_figure
def chord_symbol_midi_pitches(self, figure):
chord_symbol = self._to_music21_chord_symbol(figure)
return [pitch.midi for pitch in chord_symbol.pitches]
def chord_symbol_root(self, figure):
chord_symbol = self._to_music21_chord_symbol(figure)
return chord_symbol.root().pitchClass
def chord_symbol_quality(self, figure):
chord_symbol = self._to_music21_chord_symbol(figure)
quality_string = chord_symbol.quality
if quality_string not in self._music21_chord_quality_mapping:
return CHORD_QUALITY_OTHER
else:
return self._music21_chord_quality_mapping[quality_string]