spectrogram

Spectrogram.

Syntax

sp = spectrogram(x)

sp = spectrogram(x,fs)

sp = spectrogram(x,fs,window)

sp = spectrogram(x,fs,window,overlap)

sp = spectrogram(x,fs,window,overlap,nfft)

sp = spectrogram(x,fs,window,overlap,nfft)

sp = spectrogram(x,fs,window,overlap,nfft,range)

[sp,t,f] = spectrogram(...)

Inputs

x
The signal to be analyzed power spectrum content.
Type: double
Dimension: vector
window
The window size, or the window column vector.
Default: hann(256, 'periodic').
Type: integer | vec
Dimension: scalar | vector
overlap
The number of overlapping points in adjacent windows.
Default: 0.
Type: integer
Dimension: scalar
nfft
The size of the fft.
Default: the window length.
Type: integer
Dimension: scalar
fs
The sampling frequency.
Default: 1 Hz.
Type: double
Dimension: scalar
range
The spectrum type. The options are as follows:
  • 'onesided' (default)
  • 'onesided_dB'
  • 'twosided'
The 'onesided' option computes the spectral magnitudes and then folds the components for the negative frequencies onto the positive frequencies and returns the result.
The 'onesided_db' option returns the magnitudes of the folded spectrum in decibels.
The 'twosided' option returns the magnitudes for the full spectrum.
With no return values, the result is plotted.
The 'onesided' and 'onesided_dB' options are only for real x, and are ignored otherwise.
Type: string

Outputs

sp
The spectogram power density output, with segments stored by column.
t
The vector of times corresponding to the start of each column of sp.
Type: vector
f
The vector of frequencies corresponding to each row of sp.
Type: vector

Example

spectrogram of a linear chirp signal.


f0 = 0;
f1 = 5;
T = 10;
c = (f1 - f0) / T;
t = [0:0.1:T-0.1];
x = sin(2 * pi * ((c/2)*t.^2 + f0*t));
spectrogram(x, 10, 20, 14, 32, 'onesided');


Figure 1. spectrogram figure 1

Comments

Default values are assigned to arguments with a [] input.

The function produces power spectral density values with no compensation for the window bias. It may be useful to normalize sp by sum(win.^2), where win is the window vector.

The 'onesided' and 'onesided_dB'outputs have 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 trend line prior to calling spectrogram. The function does not automatically call detrend.