psd (MathScript RT Module Function)
Owning Class: spectral analysis
Requires: MathScript RT Module
Syntax
psd(x)
psd(x, fftsize, fs, window)
psd(x, fftsize, fs, window, noverlap)
psd(x, fftsize, fs, window, noverlap, flag)
Pxx = psd(x)
Pxx = psd(x, fftsize, fs, window)
Pxx = psd(x, fftsize, fs, window, noverlap)
Pxx = psd(x, fftsize, fs, window, noverlap, flag)
[Pxx, f] = psd(x)
[Pxx, f] = psd(x, fftsize, fs, window)
[Pxx, f] = psd(x, fftsize, fs, window, noverlap)
[Pxx, f] = psd(x, fftsize, fs, window, noverlap, flag)
Description
Uses the Welch method to estimate the power spectrum density. If you do not specify an output, this function plots the magnitude of the power spectrum in the current plot window.
Inputs
| Name | Description | ||||||
|---|---|---|---|---|---|---|---|
| x | Specifies the input sequence. | ||||||
| fftsize | Specifies the length of the FFT to perform on each segment of data. The default is the minimum of 256 and the length of x. | ||||||
| fs | Specifies the sampling frequency. The default is 2. | ||||||
| window | Specifies the window to apply to x. The length of window must be less than or equal to fftsize. The default is a Hanning window with a length of fftsize. | ||||||
| noverlap | Specifies the number of overlapping data elements between adjacent segments of data. noverlap must be less than the length of window. The default is 0. | ||||||
| flag | Specifies the method to use to preprocess x before applying the window. flag is a string that accepts the following values.
|
Outputs
| Name | Description |
|---|---|
| Pxx | Returns the power spectrum of the input signal x. If x is real, the length of Pxx is fftsize/2 + 1 for an even fftsize and (fftsize + 1) / 2 for an odd fftsize. If x is complex, the length of Pxx is fftsize. |
| f | Returns the frequencies that correspond to Pxx. |
Details
This function is similar to the psd_welch function. However, there are some slight differences between the two functions, such as different formulas and different default values for the inputs. National Instruments recommends you use the psd_welch function instead of the psd function.
This function is supported in the LabVIEW Run-Time Engine only if you request an output from the function. This function can remain in your scripts when you build a stand-alone application or shared library, but if you do not request an output, the LabVIEW Run-Time Engine does not execute this function. If you request an output, the LabVIEW Run-Time Engine executes this function as normal.
Examples
fs = 1000;
f = 100;
T = 2;
t = 0:1 / fs:T - 1 / fs;
x = sin(2*pi*f*t) + 10*t;
y = sin(2*pi*0.5*f*t) + 20*t;
fftsize = 256;
[pxx, fxx] = psd(x, fftsize, fs, win_hann2(fftsize), fftsize/2, 'linear');