scipy.signal.zoom_fft

scipy.signal.zoom_fft(x, fn, m=None, *, fs=2, endpoint=False, axis=- 1)

Compute the DFT of x only for frequencies in range fn.

Parameters

xarray

The signal to transform.

fnarray_like

A length-2 sequence [f1, f2] giving the frequency range, or a scalar, for which the range [0, fn] is assumed.

mint, optional

The number of points to evaluate. The default is the length of x.

fsfloat, optional

The sampling frequency. If fs=10 represented 10 kHz, for example, then f1 and f2 would also be given in kHz. The default sampling frequency is 2, so f1 and f2 should be in the range [0, 1] to keep the transform below the Nyquist frequency.

endpointbool, optional

If True, f2 is the last sample. Otherwise, it is not included. Default is False.

axisint, optional

Axis over which to compute the FFT. If not given, the last axis is used.

Returns

outndarray

The transformed signal. The Fourier transform will be calculated at the points f1, f1+df, f1+2df, …, f2, where df=(f2-f1)/m.

See also

ZoomFFT

Class that creates a callable partial FFT function.

Notes

The defaults are chosen such that signal.zoom_fft(x, 2) is equivalent to fft.fft(x) and, if m > len(x), that signal.zoom_fft(x, 2, m) is equivalent to fft.fft(x, m).

To graph the magnitude of the resulting transform, use:

plot(linspace(f1, f2, m, endpoint=False), abs(zoom_fft(x, [f1, f2], m)))

If the transform needs to be repeated, use ZoomFFT to construct a specialized transform function which can be reused without recomputing constants.

Examples

To plot the transform results use something like the following:

>>> from scipy.signal import zoom_fft
>>> t = np.linspace(0, 1, 1021)
>>> x = np.cos(2*np.pi*15*t) + np.sin(2*np.pi*17*t)
>>> f1, f2 = 5, 27
>>> X = zoom_fft(x, [f1, f2], len(x), fs=1021)
>>> f = np.linspace(f1, f2, len(x))
>>> import matplotlib.pyplot as plt
>>> plt.plot(f, 20*np.log10(np.abs(X)))
>>> plt.show()