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librosa.autocorrelate

librosa.autocorrelate(y, *, max_size=None, axis=-1)[source]

Bounded-lag auto-correlation

Parameters:

ynp.ndarray: array to autocorrelate
max_sizeint > 0 or None: maximum correlation lag. If unspecified, defaults to y.shape[axis] (unbounded)
axisint: The axis along which to autocorrelate. By default, the last axis (-1) is taken.

Returns:

znp.ndarray: truncated autocorrelation y*y along the specified axis. If max_size is specified, then z.shape[axis] is bounded to max_size.

Notes

This function caches at level 20.

Examples

Compute full autocorrelation of y

>>> y, sr = librosa.load(librosa.ex('trumpet'))
>>> librosa.autocorrelate(y)
array([ 6.899e+02,  6.236e+02, ...,  3.710e-08, -1.796e-08])

Compute onset strength auto-correlation up to 4 seconds

>>> import matplotlib.pyplot as plt
>>> odf = librosa.onset.onset_strength(y=y, sr=sr, hop_length=512)
>>> ac = librosa.autocorrelate(odf, max_size=4 * sr // 512)
>>> fig, ax = plt.subplots()
>>> ax.plot(ac)
>>> ax.set(title='Auto-correlation', xlabel='Lag (frames)')