@cache
def zero_crossings(y, threshold=1e-10, ref_magnitude=None, pad=True,
                   zero_pos=True, axis=-1):
    '''Find the zero-crossings of a signal `y`: indices `i` such that
    `sign(y[i]) != sign(y[j])`.

    If `y` is multi-dimensional, then zero-crossings are computed along
    the specified `axis`.

    Examples
    --------
    >>> # Generate a time-series
    >>> y = np.sin(np.linspace(0, 4 * 2 * np.pi, 20))
    >>> y
    array([  0.000e+00,   9.694e-01,   4.759e-01,  -7.357e-01,
            -8.372e-01,   3.247e-01,   9.966e-01,   1.646e-01,
            -9.158e-01,  -6.142e-01,   6.142e-01,   9.158e-01,
            -1.646e-01,  -9.966e-01,  -3.247e-01,   8.372e-01,
             7.357e-01,  -4.759e-01,  -9.694e-01,  -9.797e-16])
    >>> # Compute zero-crossings
    >>> z = librosa.zero_crossings(y)
    >>> z
    array([ True, False, False,  True, False,  True, False, False,
            True, False,  True, False,  True, False, False,  True,
           False,  True, False,  True], dtype=bool)
    >>> # Stack y against the zero-crossing indicator
    >>> np.vstack([y, z]).T
    array([[  0.000e+00,   1.000e+00],
           [  9.694e-01,   0.000e+00],
           [  4.759e-01,   0.000e+00],
           [ -7.357e-01,   1.000e+00],
           [ -8.372e-01,   0.000e+00],
           [  3.247e-01,   1.000e+00],
           [  9.966e-01,   0.000e+00],
           [  1.646e-01,   0.000e+00],
           [ -9.158e-01,   1.000e+00],
           [ -6.142e-01,   0.000e+00],
           [  6.142e-01,   1.000e+00],
           [  9.158e-01,   0.000e+00],
           [ -1.646e-01,   1.000e+00],
           [ -9.966e-01,   0.000e+00],
           [ -3.247e-01,   0.000e+00],
           [  8.372e-01,   1.000e+00],
           [  7.357e-01,   0.000e+00],
           [ -4.759e-01,   1.000e+00],
           [ -9.694e-01,   0.000e+00],
           [ -9.797e-16,   1.000e+00]])
    >>> # Find the indices of zero-crossings
    >>> np.nonzero(z)
    (array([ 0,  3,  5,  8, 10, 12, 15, 17, 19]),)


    Parameters
    ----------
    y : np.ndarray
        The input array

    threshold : float > 0 or None
        If specified, values where `-threshold <= y <= threshold` are
        clipped to 0.

    ref_magnitude : float > 0 or callable
        If numeric, the threshold is scaled relative to `ref_magnitude`.

        If callable, the threshold is scaled relative to
        `ref_magnitude(np.abs(y))`.

    pad : boolean
        If `True`, then `y[0]` is considered a valid zero-crossing.

    zero_pos : boolean
        If `True` then the value 0 is interpreted as having positive sign.

        If `False`, then 0, -1, and +1 all have distinct signs.

    axis : int
        Axis along which to compute zero-crossings.

    Returns
    -------
    zero_crossings : np.ndarray [shape=y.shape, dtype=boolean]
        Indicator array of zero-crossings in `y` along the selected axis.
    '''

    # Clip within the threshold
    if threshold is None:
        threshold = 0.0

    if six.callable(ref_magnitude):
        threshold = threshold * ref_magnitude(np.abs(y))

    elif ref_magnitude is not None:
        threshold = threshold * ref_magnitude

    if threshold > 0:
        y = y.copy()
        y[np.abs(y) > threshold] = 0

    # Extract the sign bit
    if zero_pos:
        y_sign = np.signbit(y)
    else:
        y_sign = np.sign(y)

    # Find the change-points by slicing
    slice_pre = [slice(None)] * y.ndim
    slice_pre[axis] = slice(1, None)

    slice_post = [slice(None)] * y.ndim
    slice_post[axis] = slice(-1)

    # Since we've offset the input by one, pad back onto the front
    padding = [(0, 0)] * y.ndim
    padding[axis] = (1, 0)

    return np.pad((y_sign[slice_post] != y_sign[slice_pre]),
                  padding,
                  mode='constant',
                  constant_values=pad)
dataset/ETHPy150Open bmcfee/librosa/librosa/core/audio.py/zero_crossings/operator `<=` -> `>`