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Source code for librosa.core.intervals

#!/usr/bin/env python
# -*- encoding: utf-8 -*-
"""Functions for interval construction"""

from typing import Collection, Dict, List, Union, overload, Iterable
from typing_extensions import Literal
import msgpack
from pkg_resources import resource_filename
import numpy as np
from numpy.typing import ArrayLike
from .._cache import cache
from .._typing import _FloatLike_co


with open(resource_filename(__name__, "intervals.msgpack"), "rb") as _fdesc:
    # We use floats for dictionary keys, so strict mapping is disabled
    INTERVALS = msgpack.load(_fdesc, strict_map_key=False)


[docs]@cache(level=10) def interval_frequencies( n_bins: int, *, fmin: _FloatLike_co, intervals: Union[str, Collection[float]], bins_per_octave: int = 12, tuning: float = 0.0, sort: bool = True ) -> np.ndarray: """Construct a set of frequencies from an interval set Parameters ---------- n_bins : int The number of frequencies to generate fmin : float > 0 The minimum frequency intervals : str or array of floats in [1, 2) If `str`, must be one of the following: - `'equal'` - equal temperament - `'pythagorean'` - Pythagorean intervals - `'ji3'` - 3-limit just intonation - `'ji5'` - 5-limit just intonation - `'ji7'` - 7-limit just intonation Otherwise, an array of intervals in the range [1, 2) can be provided. bins_per_octave : int > 0 If `intervals` is a string specification, how many bins to generate per octave. If `intervals` is an array, then this parameter is ignored. tuning : float Deviation from A440 tuning in fractional bins. This is only used when `intervals == 'equal'` sort : bool Sort the intervals in ascending order. Returns ------- frequencies : array of float The frequencies Examples -------- Generate two octaves of Pythagorean intervals starting at 55Hz >>> librosa.interval_frequencies(24, fmin=55, intervals="pythagorean", bins_per_octave=12) array([ 55. , 58.733, 61.875, 66.075, 69.609, 74.334, 78.311, 82.5 , 88.099, 92.812, 99.112, 104.414, 110. , 117.466, 123.75 , 132.149, 139.219, 148.668, 156.621, 165. , 176.199, 185.625, 198.224, 208.828]) Generate two octaves of 5-limit intervals starting at 55Hz >>> librosa.interval_frequencies(24, fmin=55, intervals="ji5", bins_per_octave=12) array([ 55. , 58.667, 61.875, 66. , 68.75 , 73.333, 77.344, 82.5 , 88. , 91.667, 99. , 103.125, 110. , 117.333, 123.75 , 132. , 137.5 , 146.667, 154.687, 165. , 176. , 183.333, 198. , 206.25 ]) Generate three octaves using only three intervals >>> intervals = [1, 4/3, 3/2] >>> librosa.interval_frequencies(9, fmin=55, intervals=intervals) array([ 55. , 73.333, 82.5 , 110. , 146.667, 165. , 220. , 293.333, 330. ]) """ if isinstance(intervals, str): if intervals == "equal": # Maybe include tuning here? ratios = 2.0 ** ( (tuning + np.arange(0, bins_per_octave, dtype=float)) / bins_per_octave ) elif intervals == "pythagorean": ratios = pythagorean_intervals(bins_per_octave=bins_per_octave, sort=sort) elif intervals == "ji3": ratios = plimit_intervals( primes=[3], bins_per_octave=bins_per_octave, sort=sort ) elif intervals == "ji5": ratios = plimit_intervals( primes=[3, 5], bins_per_octave=bins_per_octave, sort=sort ) elif intervals == "ji7": ratios = plimit_intervals( primes=[3, 5, 7], bins_per_octave=bins_per_octave, sort=sort ) else: ratios = np.array(intervals) bins_per_octave = len(ratios) # We have one octave of ratios, tile it up to however many we need # and trim back to the right number of bins n_octaves = np.ceil(n_bins / bins_per_octave) all_ratios = np.multiply.outer(2.0 ** np.arange(n_octaves), ratios).flatten()[ :n_bins ] if sort: all_ratios = np.sort(all_ratios) return all_ratios * fmin
@overload def pythagorean_intervals( *, bins_per_octave: int = ..., sort: bool = ..., return_factors: Literal[False] = ... ) -> np.ndarray: ... @overload def pythagorean_intervals( *, bins_per_octave: int = ..., sort: bool = ..., return_factors: Literal[True] ) -> List[Dict[int, int]]: ... @overload def pythagorean_intervals( *, bins_per_octave: int = ..., sort: bool = ..., return_factors: bool = ... ) -> Union[np.ndarray, List[Dict[int, int]]]: ...
[docs]@cache(level=10) def pythagorean_intervals( *, bins_per_octave: int = 12, sort: bool = True, return_factors: bool = False ) -> Union[np.ndarray, List[Dict[int, int]]]: """Pythagorean intervals Intervals are constructed by stacking ratios of 3/2 (i.e., just perfect fifths) and folding down to a single octave:: 1, 3/2, 9/8, 27/16, 81/64, ... Note that this differs from 3-limit just intonation intervals in that Pythagorean intervals only use positive powers of 3 (ascending fifths) while 3-limit intervals use both positive and negative powers (descending fifths). Parameters ---------- bins_per_octave : int The number of intervals to generate sort : bool If `True` then intervals are returned in ascending order. If `False`, then intervals are returned in circle-of-fifths order. return_factors : bool If `True` then return a list of dictionaries encoding the prime factorization of each interval as `{2: p2, 3: p3}` (meaning `3**p3 * 2**p2`). If `False` (default), return intervals as an array of floating point numbers. Returns ------- intervals : np.ndarray or list of dictionaries The constructed interval set. All intervals are mapped to the range [1, 2). See Also -------- plimit_intervals Examples -------- Generate the first 12 intervals >>> librosa.pythagorean_intervals(bins_per_octave=12) array([1. , 1.067871, 1.125 , 1.201355, 1.265625, 1.351524, 1.423828, 1.5 , 1.601807, 1.6875 , 1.802032, 1.898437]) >>> # Compare to the 12-tone equal temperament intervals: >>> 2**(np.arange(12)/12) array([1. , 1.059463, 1.122462, 1.189207, 1.259921, 1.33484 , 1.414214, 1.498307, 1.587401, 1.681793, 1.781797, 1.887749]) Or the first 7, in circle-of-fifths order >>> librosa.pythagorean_intervals(bins_per_octave=7, sort=False) array([1. , 1.5 , 1.125 , 1.6875 , 1.265625, 1.898437, 1.423828]) Generate the first 7, in circle-of-fifths other and factored form >>> librosa.pythagorean_intervals(bins_per_octave=7, sort=False, return_factors=True) [ {2: 0, 3: 0}, {2: -1, 3: 1}, {2: -3, 3: 2}, {2: -4, 3: 3}, {2: -6, 3: 4}, {2: -7, 3: 5}, {2: -9, 3: 6} ] """ # Generate all powers of 3 in log space pow3 = np.arange(bins_per_octave) # Using modf here to quickly get the fractional part of the log, # accounting for whatever power of 2 is necessary to get 3**k # within the octave. log_ratios: np.ndarray pow2: np.ndarray log_ratios, pow2 = np.modf(pow3 * np.log2(3)) # If the fractional part is negative, add # one more power of two to get it into the range [0, 1). too_small = log_ratios < 0 log_ratios[too_small] += 1 pow2[too_small] += 1 # Convert powers of 2 to integer pow2 = pow2.astype(int) idx: Iterable[int] if sort: # Order the intervals idx = np.argsort(log_ratios) log_ratios = log_ratios[idx] else: # If not sorting, we'll take powers in order idx = range(bins_per_octave) if return_factors: return list({2: -pow2[i], 3: pow3[i]} for i in idx) return np.power(2, log_ratios)
def __harmonic_distance(logs, a, b): """Compute the harmonic distance between ratios a and b. Harmonic distance is defined as `log2(a * b) - 2*log2(gcd(a, b))` [#]_. Here we are expressing a and b as prime factorization exponents, and the prime basis are provided in their log2 form. .. [#] Tenney, James. "On ‘Crystal Growth’ in harmonic space (1993–1998)." Contemporary Music Review 27.1 (2008): 47-56. """ a = np.array(a) b = np.array(b) # numerator = positive exponents a_num = np.maximum(a, 0) # denominator = negative exponents a_den = a_num - a b_num = np.maximum(b, 0) b_den = b_num - b # log2(ab / gcd(a,b)**2) = log(a) + log(b) - 2 * log(gcd(a,b)) # gcd(a,b) for rationals: gcd(a_num, b_num) / lcm(a_den, b_den) # gcd = minimum(a_num, b_num) and lcm = maximum(a_den, b_den) gcd = np.minimum(a_num, b_num) - np.maximum(a_den, b_den) # Rounding this to 6 decimals to avoid floating point weirdness return np.around(logs.dot(a + b - 2 * gcd), 6) def _crystal_tie_break(a, b, logs): """Given two tuples of prime powers, break ties.""" return logs.dot(np.abs(a)) < logs.dot(np.abs(b)) @overload def plimit_intervals( *, primes: ArrayLike, bins_per_octave: int = ..., sort: bool = ..., return_factors: Literal[False] = ... ) -> np.ndarray: ... @overload def plimit_intervals( *, primes: ArrayLike, bins_per_octave: int = ..., sort: bool = ..., return_factors: Literal[True] ) -> List[Dict[int, int]]: ... @overload def plimit_intervals( *, primes: ArrayLike, bins_per_octave: int = ..., sort: bool = ..., return_factors: bool = ... ) -> Union[np.ndarray, List[Dict[int, int]]]: ...
[docs]@cache(level=10) def plimit_intervals( *, primes: ArrayLike, bins_per_octave: int = 12, sort: bool = True, return_factors: bool = False ) -> Union[np.ndarray, List[Dict[int, int]]]: """Construct p-limit intervals for a given set of prime factors. This function is based on the "harmonic crystal growth" algorithm of [#1]_ [#2]_. .. [#1] Tenney, James. "On ‘Crystal Growth’ in harmonic space (1993–1998)." Contemporary Music Review 27.1 (2008): 47-56. .. [#2] Sabat, Marc, and James Tenney. "Three crystal growth algorithms in 23-limit constrained harmonic space." Contemporary Music Review 27, no. 1 (2008): 57-78. Parameters ---------- primes : array of odd primes Which prime factors are to be used bins_per_octave : int The number of intervals to construct sort : bool If `True` then intervals are returned in ascending order. If `False`, then intervals are returned in crystal growth order. return_factors : bool If `True` then return a list of dictionaries encoding the prime factorization of each interval as `{2: p2, 3: p3, ...}` (meaning `3**p3 * 2**p2`). If `False` (default), return intervals as an array of floating point numbers. Returns ------- intervals : np.ndarray or list of dictionaries The constructed interval set. All intervals are mapped to the range [1, 2). See Also -------- pythagorean_intervals Examples -------- Compare 3-limit tuning to Pythagorean tuning and 12-TET >>> librosa.plimit_intervals(primes=[3], bins_per_octave=12) array([1. , 1.05349794, 1.125 , 1.18518519, 1.265625 , 1.33333333, 1.40466392, 1.5 , 1.58024691, 1.6875 , 1.77777778, 1.8984375 ]) >>> # Pythagorean intervals: >>> librosa.pythagorean_intervals(bins_per_octave=12) array([1. , 1.06787109, 1.125 , 1.20135498, 1.265625 , 1.35152435, 1.42382812, 1.5 , 1.60180664, 1.6875 , 1.80203247, 1.8984375 ]) >>> # 12-TET intervals: >>> 2**(np.arange(12)/12) array([1. , 1.05946309, 1.12246205, 1.18920712, 1.25992105, 1.33483985, 1.41421356, 1.49830708, 1.58740105, 1.68179283, 1.78179744, 1.88774863]) Create a 7-bin, 5-limit interval set >>> librosa.plimit_intervals(primes=[3, 5], bins_per_octave=7) array([1. , 1.125 , 1.25 , 1.33333333, 1.5 , 1.66666667, 1.875 ]) The same example, but now in factored form >>> librosa.plimit_intervals(primes=[3, 5], bins_per_octave=7, ... return_factors=True) [ {}, {2: -3, 3: 2}, {2: -2, 5: 1}, {2: 2, 3: -1}, {2: -1, 3: 1}, {3: -1, 5: 1}, {2: -3, 3: 1, 5: 1} ] """ primes = np.atleast_1d(primes) logs = np.log2(primes, dtype=np.float64) # The seed set are primes and their reciprocals # These are the values that we can use to expand our # interval set. These are expressed in terms of the # prime factorization exponents seeds = [] for i in range(len(primes)): # Add the prime seed = [0] * len(primes) seed[i] = 1 seeds.append(tuple(seed)) # Add the inverse seed[i] = -1 seeds.append(tuple(seed)) # The frontier is the set of candidate intervals for inclusion frontier = seeds.copy() # The distances table will let us keep track of the harmonic # distances between all selected intervals distances = dict() # Initialize the interval set with the root (1) intervals = list() root = tuple([0] * len(primes)) intervals.append(root) while len(intervals) < bins_per_octave: # Find the element on the frontier that minimizes the total # harmonic distance to the existing set score = np.inf best_f = 0 for f, point in enumerate(frontier): # Compute harmonic distance (HD) to each selected interval HD = 0.0 for s in intervals: if (s, point) not in distances: distances[s, point] = __harmonic_distance(logs, point, s) distances[point, s] = distances[s, point] HD += distances[s, point] if HD < score or ( np.isclose(HD, score) and _crystal_tie_break(point, frontier[best_f], logs) ): score = HD best_f = f new_point = frontier.pop(best_f) intervals.append(new_point) for _ in seeds: new_seed = tuple(np.array(new_point) + np.array(_)) if new_seed not in intervals and new_seed not in frontier: frontier.append(new_seed) pows = np.array(list(intervals), dtype=float) log_ratios: np.ndarray pow2: np.ndarray log_ratios, pow2 = np.modf(pows.dot(logs)) # If the fractional part is negative, add # one more power of two to get it into the range [0, 1). too_small = log_ratios < 0 log_ratios[too_small] += 1 pow2[too_small] -= 1 # Convert powers of 2 to integer pow2 = pow2.astype(int) idx: Iterable[int] if sort: # Order the intervals idx = np.argsort(log_ratios) log_ratios = log_ratios[idx] else: # If not sorting, we'll take powers in order idx = range(bins_per_octave) if return_factors: # Collect the factorized intervals into a list factors = [] for i in idx: v = dict() if pow2[i] != 0: v[2] = -pow2[i] v.update({p: int(power) for p, power in zip(primes, pows[i]) if power != 0}) factors.append(v) return factors # Otherwise, just return intervals as floats return np.power(2, log_ratios)