scipy.signal.

resample#

scipy.signal.resample(x, num, t=None, axis=0, window=None, domain='time')[source]#

Resample x to num samples using Fourier method along the given axis.

The resampled signal starts at the same value as x but is sampled with a spacing of len(x) / num * (spacing of x). Because a Fourier method is used, the signal is assumed to be periodic.

Parameters:

xarray_like: The data to be resampled.
numint: The number of samples in the resampled signal.
tarray_like, optional: If t is given, it is assumed to be the equally spaced sample positions associated with the signal data in x.
axisint, optional: The axis of x that is resampled. Default is 0.
windowarray_like, callable, string, float, or tuple, optional: Specifies the window applied to the signal in the Fourier domain. See below for details.
domainstring, optional: A string indicating the domain of the input x: time Consider the input x as time-domain (Default), freq Consider the input x as frequency-domain.

Returns:

resampled_x or (resampled_x, resampled_t): Either the resampled array, or, if t was given, a tuple containing the resampled array and the corresponding resampled positions.

See also

decimate: Downsample the signal after applying an FIR or IIR filter.
resample_poly: Resample using polyphase filtering and an FIR filter.

Notes

The argument window controls a Fourier-domain window that tapers the Fourier spectrum before zero-padding to alleviate ringing in the resampled values for sampled signals you didn’t intend to be interpreted as band-limited.

If window is a function, then it is called with a vector of inputs indicating the frequency bins (i.e. fftfreq(x.shape[axis]) ).

If window is an array of the same length as x.shape[axis] it is assumed to be the window to be applied directly in the Fourier domain (with dc and low-frequency first).

For any other type of window, the function scipy.signal.get_window is called to generate the window.

The first sample of the returned vector is the same as the first sample of the input vector. The spacing between samples is changed from dx to dx * len(x) / num.

If t is not None, then it is used solely to calculate the resampled positions resampled_t

As noted, resample uses FFT transformations, which can be very slow if the number of input or output samples is large and prime; see fft. In such cases, it can be faster to first downsample a signal of length n with resample_poly by a factor of n//num before using resample. Note that this approach changes the characteristics of the antialiasing filter.

Examples

Note that the end of the resampled data rises to meet the first sample of the next cycle:

>>> import numpy as np
>>> from scipy import signal

>>> x = np.linspace(0, 10, 20, endpoint=False)
>>> y = np.cos(-x**2/6.0)
>>> f = signal.resample(y, 100)
>>> xnew = np.linspace(0, 10, 100, endpoint=False)

>>> import matplotlib.pyplot as plt
>>> plt.plot(x, y, 'go-', xnew, f, '.-', 10, y[0], 'ro')
>>> plt.legend(['data', 'resampled'], loc='best')
>>> plt.show()

../../_images/scipy-signal-resample-1_00_00.png

Consider the following signal y where len(y) is a large prime number:

>>> N = 55949
>>> freq = 100
>>> x = np.linspace(0, 1, N)
>>> y = np.cos(2 * np.pi * freq * x)

Due to N being prime,

>>> num = 5000  
>>> f = signal.resample(signal.resample_poly(y, 1, N // num), num)

runs significantly faster than

>>> f = signal.resample(y, num)