pwelch

Syntax

Pxx=pwelch(x)

Pxx=pwelch(x,window)

Pxx=pwelch(x,window,overlap)

Pxx=pwelch(x,window,overlap,nfft)

Pxx=pwelch(x,window,overlap,nfft,fs)

Pxx=pwelch(x,window,overlap,nfft,fs,range)

[Pxx,freq]=pwelch(...)

pwelch(...)

Inputs

x

The signal.

Type: double

Dimension: vector | matrix

window

The window size, or the window vector.

Type: double | integer

Dimension: scalar | vector

overlap

The number of overlapping points in adjacent windows.

Type: integer

Dimension: scalar

nfft

The size of the fft.

Type: integer

Dimension: scalar

fs

The sampling frequency.

Type: double

Dimension: scalar

range

The spectrum type: 'onesided' or 'twosided'.

Type: string

Outputs

Pxx

The power spectral density.

Type: vector

freq

The vector of frequencies corresponding to the density values.

Type: vector

Example

n = 1000;                           
fs = 1125;                             
ts = 1/fs;              
t = [0:1:(n-1)]*ts;
f1 = 24;
f2 = 56;
omega1 = 2 * pi * f1;
omega2 = 2 * pi * f2;
signal = 3 + 5 * cos(omega1 * t) + 7 * cos(omega2 * t);
window = hann(250,'periodic');
overlap = 125;
fftsize = 250;
range = 'onesided';
[Pxx,frq]=pwelch(signal,window,overlap,fftsize,fs,range);
f = frq([1, 2, 3, 4, 5, 13, 14, 15])'
p = Pxx([1, 2, 3, 4, 5, 13, 14, 15])'

f = [Matrix] 1 x 8
0  4  20  24  28  52  56  60
p = [Matrix] 1 x 8
1.50000  0.75000  0.52083  2.08333  0.52083  1.02083  4.08333  1.02083

Comments

With no return arguments, the function will automatically plot.

The 'onesided' output has a length of nfft/2+1 if nfft is even, or (nfft+1)/2 if nfft is odd.

It is often recommended to remove the signal mean prior to calling pwelch. The function does not remove the mean automatically.

Comments

When x is a 2D matrix pwelch will operate on each column and the output vectors will be stored in the columns of Pxx.