Caution
You're reading the documentation for a development version. For the latest released version, please have a look at 0.10.2.
Source code for librosa.beat
#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
Beat and tempo
==============
.. autosummary::
:toctree: generated/
beat_track
plp
"""
import numpy as np
import scipy
import scipy.stats
import numba
from ._cache import cache
from . import core
from . import onset
from . import util
from .feature import tempogram, fourier_tempogram
from .feature import tempo as _tempo
from .util.exceptions import ParameterError
from .util.decorators import moved, vectorize
from typing import Any, Callable, Optional, Tuple, Union
from ._typing import _FloatLike_co
__all__ = ["beat_track", "tempo", "plp"]
tempo = moved(moved_from="librosa.beat.tempo", version="0.10.0", version_removed="1.0")(
_tempo
)
[docs]def beat_track(
*,
y: Optional[np.ndarray] = None,
sr: float = 22050,
onset_envelope: Optional[np.ndarray] = None,
hop_length: int = 512,
start_bpm: float = 120.0,
tightness: float = 100,
trim: bool = True,
bpm: Optional[Union[_FloatLike_co, np.ndarray]] = None,
prior: Optional[scipy.stats.rv_continuous] = None,
units: str = "frames",
sparse: bool = True
) -> Tuple[Union[_FloatLike_co, np.ndarray], np.ndarray]:
r"""Dynamic programming beat tracker.
Beats are detected in three stages, following the method of [#]_:
1. Measure onset strength
2. Estimate tempo from onset correlation
3. Pick peaks in onset strength approximately consistent with estimated
tempo
.. [#] Ellis, Daniel PW. "Beat tracking by dynamic programming."
Journal of New Music Research 36.1 (2007): 51-60.
http://labrosa.ee.columbia.edu/projects/beattrack/
Parameters
----------
y : np.ndarray [shape=(..., n)] or None
audio time series
sr : number > 0 [scalar]
sampling rate of ``y``
onset_envelope : np.ndarray [shape=(..., m)] or None
(optional) pre-computed onset strength envelope.
hop_length : int > 0 [scalar]
number of audio samples between successive ``onset_envelope`` values
start_bpm : float > 0 [scalar]
initial guess for the tempo estimator (in beats per minute)
tightness : float [scalar]
tightness of beat distribution around tempo
trim : bool [scalar]
trim leading/trailing beats with weak onsets
bpm : float [scalar] or np.ndarray [shape=(...)]
(optional) If provided, use ``bpm`` as the tempo instead of
estimating it from ``onsets``.
If multichannel, tempo estimates can be provided for all channels.
Tempo estimates may also be time-varying, in which case the shape
of ``bpm`` should match that of ``onset_envelope``, i.e.,
one estimate provided for each frame.
prior : scipy.stats.rv_continuous [optional]
An optional prior distribution over tempo.
If provided, ``start_bpm`` will be ignored.
units : {'frames', 'samples', 'time'}
The units to encode detected beat events in.
By default, 'frames' are used.
sparse : bool
If ``True`` (default), detections are returned as an array of frames,
samples, or time indices (as specified by ``units=``).
If ``False``, detections are encoded as a dense boolean array where
``beats[..., n]`` is true if there's a beat at frame index ``n``.
.. note:: multi-channel input is only supported when ``sparse=False``.
Returns
-------
tempo : float [scalar, non-negative] or np.ndarray
estimated global tempo (in beats per minute)
If multi-channel and ``bpm`` is not provided, a separate
tempo will be returned for each channel
beats : np.ndarray
estimated beat event locations.
If `sparse=True` (default), beat locations are given in the specified units
(default is frame indices).
If `sparse=False` (required for multichannel input), beat events are
indicated by a boolean for each frame.
.. note::
If no onset strength could be detected, beat_tracker estimates 0 BPM
and returns an empty list.
Raises
------
ParameterError
if neither ``y`` nor ``onset_envelope`` are provided,
or if ``units`` is not one of 'frames', 'samples', or 'time'
See Also
--------
librosa.onset.onset_strength
Examples
--------
Track beats using time series input
>>> y, sr = librosa.load(librosa.ex('choice'), duration=10)
>>> tempo, beats = librosa.beat.beat_track(y=y, sr=sr)
>>> tempo
135.99917763157896
Print the frames corresponding to beats
>>> beats
array([ 3, 21, 40, 59, 78, 96, 116, 135, 154, 173, 192, 211,
230, 249, 268, 287, 306, 325, 344, 363])
Or print them as timestamps
>>> librosa.frames_to_time(beats, sr=sr)
array([0.07 , 0.488, 0.929, 1.37 , 1.811, 2.229, 2.694, 3.135,
3.576, 4.017, 4.458, 4.899, 5.341, 5.782, 6.223, 6.664,
7.105, 7.546, 7.988, 8.429])
Output beat detections as a boolean array instead of frame indices
>>> tempo, beats_dense = librosa.beat.beat_track(y=y, sr=sr, sparse=False)
>>> beats_dense
array([False, False, False, True, False, False, False, False,
False, False, False, False, False, False, False, False,
False, False, False, False, ..., False, False, True,
False, False, False, False, False, False, False, False,
False, False, False, False, False, False, False, False,
False])
Track beats using a pre-computed onset envelope
>>> onset_env = librosa.onset.onset_strength(y=y, sr=sr,
... aggregate=np.median)
>>> tempo, beats = librosa.beat.beat_track(onset_envelope=onset_env,
... sr=sr)
>>> tempo
135.99917763157896
>>> beats
array([ 3, 21, 40, 59, 78, 96, 116, 135, 154, 173, 192, 211,
230, 249, 268, 287, 306, 325, 344, 363])
Plot the beat events against the onset strength envelope
>>> import matplotlib.pyplot as plt
>>> hop_length = 512
>>> fig, ax = plt.subplots(nrows=2, sharex=True)
>>> times = librosa.times_like(onset_env, sr=sr, hop_length=hop_length)
>>> M = librosa.feature.melspectrogram(y=y, sr=sr, hop_length=hop_length)
>>> librosa.display.specshow(librosa.power_to_db(M, ref=np.max),
... y_axis='mel', x_axis='time', hop_length=hop_length,
... ax=ax[0])
>>> ax[0].label_outer()
>>> ax[0].set(title='Mel spectrogram')
>>> ax[1].plot(times, librosa.util.normalize(onset_env),
... label='Onset strength')
>>> ax[1].vlines(times[beats], 0, 1, alpha=0.5, color='r',
... linestyle='--', label='Beats')
>>> ax[1].legend()
"""
# First, get the frame->beat strength profile if we don't already have one
if onset_envelope is None:
if y is None:
raise ParameterError("y or onset_envelope must be provided")
onset_envelope = onset.onset_strength(
y=y, sr=sr, hop_length=hop_length, aggregate=np.median
)
if sparse and onset_envelope.ndim != 1:
raise ParameterError(f"sparse=True (default) does not support "
f"{onset_envelope.ndim}-dimensional inputs. "
f"Either set sparse=False or convert the signal to mono.")
# Do we have any onsets to grab?
if not onset_envelope.any():
if sparse:
return (0.0, np.array([], dtype=int))
else:
return (np.zeros(shape=onset_envelope.shape[:-1], dtype=float),
np.zeros_like(onset_envelope, dtype=bool))
# Estimate BPM if one was not provided
if bpm is None:
bpm = _tempo(
onset_envelope=onset_envelope,
sr=sr,
hop_length=hop_length,
start_bpm=start_bpm,
prior=prior,
)
# Ensure that tempo is in a shape that is compatible with vectorization
_bpm = np.atleast_1d(bpm)
bpm_expanded = util.expand_to(_bpm,
ndim=onset_envelope.ndim,
axes=range(_bpm.ndim))
# Then, run the tracker
beats = __beat_tracker(onset_envelope, bpm_expanded, float(sr) / hop_length, tightness, trim)
if sparse:
beats = np.flatnonzero(beats)
if units == "frames":
pass
elif units == "samples":
return (bpm, core.frames_to_samples(beats, hop_length=hop_length))
elif units == "time":
return (bpm, core.frames_to_time(beats, hop_length=hop_length, sr=sr))
else:
raise ParameterError(f"Invalid unit type: {units}")
return (bpm, beats)
[docs]def plp(
*,
y: Optional[np.ndarray] = None,
sr: float = 22050,
onset_envelope: Optional[np.ndarray] = None,
hop_length: int = 512,
win_length: int = 384,
tempo_min: Optional[float] = 30,
tempo_max: Optional[float] = 300,
prior: Optional[scipy.stats.rv_continuous] = None,
) -> np.ndarray:
"""Predominant local pulse (PLP) estimation. [#]_
The PLP method analyzes the onset strength envelope in the frequency domain
to find a locally stable tempo for each frame. These local periodicities
are used to synthesize local half-waves, which are combined such that peaks
coincide with rhythmically salient frames (e.g. onset events on a musical time grid).
The local maxima of the pulse curve can be taken as estimated beat positions.
This method may be preferred over the dynamic programming method of `beat_track`
when the tempo is expected to vary significantly over time. Additionally,
since `plp` does not require the entire signal to make predictions, it may be
preferable when beat-tracking long recordings in a streaming setting.
.. [#] Grosche, P., & Muller, M. (2011).
"Extracting predominant local pulse information from music recordings."
IEEE Transactions on Audio, Speech, and Language Processing, 19(6), 1688-1701.
Parameters
----------
y : np.ndarray [shape=(..., n)] or None
audio time series. Multi-channel is supported.
sr : number > 0 [scalar]
sampling rate of ``y``
onset_envelope : np.ndarray [shape=(..., n)] or None
(optional) pre-computed onset strength envelope
hop_length : int > 0 [scalar]
number of audio samples between successive ``onset_envelope`` values
win_length : int > 0 [scalar]
number of frames to use for tempogram analysis.
By default, 384 frames (at ``sr=22050`` and ``hop_length=512``) corresponds
to about 8.9 seconds.
tempo_min, tempo_max : numbers > 0 [scalar], optional
Minimum and maximum permissible tempo values. ``tempo_max`` must be at least
``tempo_min``.
Set either (or both) to `None` to disable this constraint.
prior : scipy.stats.rv_continuous [optional]
A prior distribution over tempo (in beats per minute).
By default, a uniform prior over ``[tempo_min, tempo_max]`` is used.
Returns
-------
pulse : np.ndarray, shape=[(..., n)]
The estimated pulse curve. Maxima correspond to rhythmically salient
points of time.
If input is multi-channel, one pulse curve per channel is computed.
See Also
--------
beat_track
librosa.onset.onset_strength
librosa.feature.fourier_tempogram
Examples
--------
Visualize the PLP compared to an onset strength envelope.
Both are normalized here to make comparison easier.
>>> y, sr = librosa.load(librosa.ex('brahms'))
>>> onset_env = librosa.onset.onset_strength(y=y, sr=sr)
>>> pulse = librosa.beat.plp(onset_envelope=onset_env, sr=sr)
>>> # Or compute pulse with an alternate prior, like log-normal
>>> import scipy.stats
>>> prior = scipy.stats.lognorm(loc=np.log(120), scale=120, s=1)
>>> pulse_lognorm = librosa.beat.plp(onset_envelope=onset_env, sr=sr,
... prior=prior)
>>> melspec = librosa.feature.melspectrogram(y=y, sr=sr)
>>> import matplotlib.pyplot as plt
>>> fig, ax = plt.subplots(nrows=3, sharex=True)
>>> librosa.display.specshow(librosa.power_to_db(melspec,
... ref=np.max),
... x_axis='time', y_axis='mel', ax=ax[0])
>>> ax[0].set(title='Mel spectrogram')
>>> ax[0].label_outer()
>>> ax[1].plot(librosa.times_like(onset_env),
... librosa.util.normalize(onset_env),
... label='Onset strength')
>>> ax[1].plot(librosa.times_like(pulse),
... librosa.util.normalize(pulse),
... label='Predominant local pulse (PLP)')
>>> ax[1].set(title='Uniform tempo prior [30, 300]')
>>> ax[1].label_outer()
>>> ax[2].plot(librosa.times_like(onset_env),
... librosa.util.normalize(onset_env),
... label='Onset strength')
>>> ax[2].plot(librosa.times_like(pulse_lognorm),
... librosa.util.normalize(pulse_lognorm),
... label='Predominant local pulse (PLP)')
>>> ax[2].set(title='Log-normal tempo prior, mean=120', xlim=[5, 20])
>>> ax[2].legend()
PLP local maxima can be used as estimates of beat positions.
>>> tempo, beats = librosa.beat.beat_track(onset_envelope=onset_env)
>>> beats_plp = np.flatnonzero(librosa.util.localmax(pulse))
>>> import matplotlib.pyplot as plt
>>> fig, ax = plt.subplots(nrows=2, sharex=True, sharey=True)
>>> times = librosa.times_like(onset_env, sr=sr)
>>> ax[0].plot(times, librosa.util.normalize(onset_env),
... label='Onset strength')
>>> ax[0].vlines(times[beats], 0, 1, alpha=0.5, color='r',
... linestyle='--', label='Beats')
>>> ax[0].legend()
>>> ax[0].set(title='librosa.beat.beat_track')
>>> ax[0].label_outer()
>>> # Limit the plot to a 15-second window
>>> times = librosa.times_like(pulse, sr=sr)
>>> ax[1].plot(times, librosa.util.normalize(pulse),
... label='PLP')
>>> ax[1].vlines(times[beats_plp], 0, 1, alpha=0.5, color='r',
... linestyle='--', label='PLP Beats')
>>> ax[1].legend()
>>> ax[1].set(title='librosa.beat.plp', xlim=[5, 20])
>>> ax[1].xaxis.set_major_formatter(librosa.display.TimeFormatter())
"""
# Step 1: get the onset envelope
if onset_envelope is None:
onset_envelope = onset.onset_strength(
y=y, sr=sr, hop_length=hop_length, aggregate=np.median
)
if tempo_min is not None and tempo_max is not None and tempo_max <= tempo_min:
raise ParameterError(
f"tempo_max={tempo_max} must be larger than tempo_min={tempo_min}"
)
# Step 2: get the fourier tempogram
ftgram = fourier_tempogram(
onset_envelope=onset_envelope,
sr=sr,
hop_length=hop_length,
win_length=win_length,
)
# Step 3: pin to the feasible tempo range
tempo_frequencies = core.fourier_tempo_frequencies(
sr=sr, hop_length=hop_length, win_length=win_length
)
if tempo_min is not None:
ftgram[..., tempo_frequencies < tempo_min, :] = 0
if tempo_max is not None:
ftgram[..., tempo_frequencies > tempo_max, :] = 0
# reshape lengths to match dimension properly
tempo_frequencies = util.expand_to(tempo_frequencies, ndim=ftgram.ndim, axes=-2)
# Step 3: Discard everything below the peak
ftmag = np.log1p(1e6 * np.abs(ftgram))
if prior is not None:
ftmag += prior.logpdf(tempo_frequencies)
peak_values = ftmag.max(axis=-2, keepdims=True)
ftgram[ftmag < peak_values] = 0
# Normalize to keep only phase information
ftgram /= util.tiny(ftgram) ** 0.5 + np.abs(ftgram.max(axis=-2, keepdims=True))
# Step 5: invert the Fourier tempogram to get the pulse
pulse = core.istft(
ftgram, hop_length=1, n_fft=win_length, length=onset_envelope.shape[-1]
)
# Step 6: retain only the positive part of the pulse cycle
pulse = np.clip(pulse, 0, None, pulse)
# Return the normalized pulse
return util.normalize(pulse, axis=-1)
def __beat_tracker(
onset_envelope: np.ndarray, bpm: np.ndarray, frame_rate: float, tightness: float, trim: bool
) -> np.ndarray:
"""Tracks beats in an onset strength envelope.
Parameters
----------
onset_envelope : np.ndarray [shape=(..., n,)]
onset strength envelope
bpm : float [scalar] or np.ndarray [shape=(...)]
tempo estimate
frame_rate : float [scalar]
frame rate of the spectrogram (sr / hop_length, frames per second)
tightness : float [scalar, positive]
how closely do we adhere to bpm?
trim : bool [scalar]
trim leading/trailing beats with weak onsets?
Returns
-------
beats : np.ndarray [shape=(n,)]
frame numbers of beat events
"""
if np.any(bpm <= 0):
raise ParameterError(f"bpm={bpm} must be strictly positive")
if tightness <= 0:
raise ParameterError("tightness must be strictly positive")
# TODO: this might be better accomplished with a np.broadcast_shapes check
if bpm.shape[-1] not in (1, onset_envelope.shape[-1]):
raise ParameterError(f"Invalid bpm shape={bpm.shape} does not match onset envelope shape={onset_envelope.shape}")
# convert bpm to frames per beat (rounded)
# [frames / sec] * [60 sec / min] / [beat / min] = [frames / beat]
frames_per_beat = np.round(frame_rate * 60.0 / bpm)
# localscore is a smoothed version of AGC'd onset envelope
localscore = __beat_local_score(__normalize_onsets(onset_envelope), frames_per_beat)
# run the DP
backlink, cumscore = __beat_track_dp(localscore, frames_per_beat, tightness)
# Reconstruct the beat path from backlinks
tail = __last_beat(cumscore)
beats = np.zeros_like(onset_envelope, dtype=bool)
__dp_backtrack(backlink, tail, beats)
# Discard spurious trailing beats
beats: np.ndarray = __trim_beats(localscore, beats, trim)
return beats
# -- Helper functions for beat tracking
def __normalize_onsets(onsets):
"""Normalize onset strength by its standard deviation"""
norm = onsets.std(ddof=1, axis=-1, keepdims=True)
return onsets / (norm + util.tiny(onsets))
@numba.guvectorize(
[
"void(float32[:], float32[:], float32[:])",
"void(float64[:], float64[:], float64[:])",
],
"(t),(n)->(t)",
nopython=True, cache=False)
def __beat_local_score(onset_envelope, frames_per_beat, localscore):
# This function essentially implements a same-mode convolution,
# but also allows for a time-varying convolution-like filter to support dynamic tempo.
N = len(onset_envelope)
if len(frames_per_beat) == 1:
# Static tempo mode
# NOTE: when we can bump the minimum numba to 0.58, we can eliminate this branch and just use
# np.convolve(..., mode='same') directly
window = np.exp(-0.5 * (np.arange(-frames_per_beat[0], frames_per_beat[0] + 1) * 32.0 / frames_per_beat[0]) ** 2)
K = len(window)
# This is a vanilla same-mode convolution
for i in range(len(onset_envelope)):
localscore[i] = 0.
# we need i + K // 2 - k < N ==> k > i + K //2 - N
# and i + K // 2 - k >= 0 ==> k <= i + K // 2
for k in range(max(0, i + K // 2 - N + 1), min(i + K // 2, K)):
localscore[i] += window[k] * onset_envelope[i + K//2 -k]
elif len(frames_per_beat) == len(onset_envelope):
# Time-varying tempo estimates
# This isn't exactly a convolution anymore, since the filter is time-varying, but it's pretty close
for i in range(len(onset_envelope)):
window = np.exp(-0.5 * (np.arange(-frames_per_beat[i], frames_per_beat[i] + 1) * 32.0 / frames_per_beat[i]) ** 2)
K = 2 * int(frames_per_beat[i]) + 1
localscore[i] = 0.
for k in range(max(0, i + K // 2 - N + 1), min(i + K // 2, K)):
localscore[i] += window[k] * onset_envelope[i + K // 2 - k]
@numba.guvectorize(
[
"void(float32[:], float32[:], float32, int32[:], float32[:])",
"void(float64[:], float64[:], float32, int32[:], float64[:])",
],
"(t),(n),()->(t),(t)",
nopython=True, cache=True)
def __beat_track_dp(localscore, frames_per_beat, tightness, backlink, cumscore):
"""Core dynamic program for beat tracking"""
# Threshold for the first beat to exceed
score_thresh = 0.01 * localscore.max()
# Are we on the first beat?
first_beat = True
backlink[0] = -1
cumscore[0] = localscore[0]
# If tv == 0, then tv * i will always be 0, so we only ever use frames_per_beat[0]
# If tv == 1, then tv * i = i, so we use the time-varying FPB
tv = int(len(frames_per_beat) > 1)
for i, score_i in enumerate(localscore):
best_score = - np.inf
beat_location = -1
# Search over all possible predecessors to find the best preceding beat
# NOTE: to provide time-varying tempo estimates, we replace
# frames_per_beat[0] by frames_per_beat[i] in this loop body.
for loc in range(i - np.round(frames_per_beat[tv * i] / 2), i - 2 * frames_per_beat[tv * i] - 1, - 1):
# Once we're searching past the start, break out
if loc < 0:
break
score = cumscore[loc] - tightness * (np.log(i - loc) - np.log(frames_per_beat[tv * i]))**2
if score > best_score:
best_score = score
beat_location = loc
# Add the local score
if beat_location >= 0:
cumscore[i] = score_i + best_score
else:
# No back-link found, so just use the current score
cumscore[i] = score_i
# Special case the first onset. Stop if the localscore is small
if first_beat and score_i < score_thresh:
backlink[i] = -1
else:
backlink[i] = beat_location
first_beat = False
@numba.guvectorize(
[
"void(float32[:], bool_[:], bool_, bool_[:])",
"void(float64[:], bool_[:], bool_, bool_[:])"
],
"(t),(t),()->(t)",
nopython=True, cache=True
)
def __trim_beats(localscore, beats, trim, beats_trimmed):
"""Remove spurious leading and trailing beats from the detection array"""
# Populate the trimmed beats array with the existing values
beats_trimmed[:] = beats
# Compute the threshold: 1/2 RMS of the smoothed beat envelope
w = np.hanning(5)
# Slicing here to implement same-mode convolution in older numba where
# mode='same' is not yet supported
smooth_boe = np.convolve(localscore[beats], w)[len(w)//2:len(localscore)+len(w)//2]
# This logic is to preserve old behavior and always discard beats detected with oenv==0
if trim:
threshold = 0.5 * ((smooth_boe**2).mean()**0.5)
else:
threshold = 0.0
# Suppress bad beats
n = 0
while localscore[n] <= threshold:
beats_trimmed[n] = False
n += 1
n = len(localscore) - 1
while localscore[n] <= threshold:
beats_trimmed[n] = False
n -= 1
pass
def __last_beat(cumscore):
"""Identify the position of the last detected beat"""
# Use a masked array to support multidimensional statistics
# We negate the mask here because of numpy masked array semantics
mask = ~util.localmax(cumscore, axis=-1)
masked_scores = np.ma.masked_array(data=cumscore, mask=mask) # type: ignore
medians = np.ma.median(masked_scores, axis=-1)
thresholds = 0.5 * np.ma.getdata(medians)
# Also find the last beat positions
tail = np.empty(shape=cumscore.shape[:-1], dtype=int)
__last_beat_selector(cumscore, mask, thresholds, tail)
return tail
@numba.guvectorize(
[
"void(float32[:], bool_[:], float32, int64[:])",
"void(float64[:], bool_[:], float64, int64[:])",
],
"(t),(t),()->()",
nopython=True, cache=True
)
def __last_beat_selector(cumscore, mask, threshold, out):
"""Vectorized helper to identify the last valid beat position:
cumscore[n] > threshold and not mask[n]
"""
n = len(cumscore) - 1
out[0] = n
while n >= 0:
if not mask[n] and cumscore[n] >= threshold:
out[0] = n
break
else:
n -= 1
@numba.guvectorize(
[
"void(int32[:], int32, bool_[:])",
"void(int64[:], int64, bool_[:])"
],
"(t),()->(t)",
nopython=True, cache=True
)
def __dp_backtrack(backlinks, tail, beats):
"""Populate the beat indicator array from a sequence of backlinks"""
n = tail
while n >= 0:
beats[n] = True
n = backlinks[n]