frequency

frequency(x, y, filter_window=5, filter_dim=2)

Get frequency of oscillating signal.

First this tries FFT. If the true value is likely below or near the frequency resolution, the function tries low frequency fit with

$$f_{\mathrm{e}\mathrm{s}\mathrm{t}}=\frac{1}{2\pi \mathrm{m}\mathrm{a}\mathrm{x}\left|y\right|}\mathrm{m}\mathrm{a}\mathrm{x}\left|\frac{dy}{dx}\right|$$

given $y=A\cos (2\pi fx+phi)$. In this mode, y data points are smoothed by a Savitzky-Golay filter to protect against outlier points.

Note

This function returns always positive frequency. This function is sensitive to the DC offset. This function assumes sorted, no-overlapping x values.

Parameters:

• x (ndarray) – Array of x values.

• y (ndarray) – Array of y values.

• filter_window (int) – Window size of Savitzky-Golay filter. This should be odd number.

• filter_dim (int) – Dimension of Savitzky-Golay filter.

Returns:

Frequency estimation of oscillation signal.

Return type:

float