Spectrogram (Short-time FT log magnitude)

Computes the Short-time Fourier transform and displays as grayscale image or 3-D surface

Description

This program is a modification and extension to Paul Kienzle's spectrogram program for Octave. It is for Matlab 6r12.1. The short-time fourier transform of a signal is computed by FFTs of overlapping windowed signal segments. You can then exit with the complete STFT, as a matrix, or you can go on to plot first a grayscale pseudocolor spectrogram with interpolated shading, and then a color 3-D surface spectrogram viewed from an optimum angle.
I made this because the specgram function in the Matlab toolbox is a joke, it doesn't even use a Fast Fourier Transform, electing to compute the DFT directly in its algorithm. Second, neither that algorithm nor Paul's original program used the pseudo plot, which allows interpolated shading of the colors, which makes the spectrogram look acceptable. The other way (i.e.\ Matlab SP toolbox, Paul's program) of displaying a 2-D plot with a third dimension as color is through an indexed image, but this doesn't allow interpolated shading, and so the spectrograms are totally useless for speech analysis.

• MATLAB release: MATLAB 6.1 (R12.1)

[mohammed benbrahim]

 

[D.S. Peterson]

a bit wordy, but looks better than matlab's default specgram, even with jet

[Don Orofino]

Have you tried "specgramdemo" shipping with the Signal Processing Toolbox? It provides an interactive GUI that might meet your need (including interactive colormap scaling ... it does not turn on "interpolated shading", however)

BTW, specgram does call FFT if frequency bins are equally spaced (which is the most typical usage)

[w w]

 

[David Michael]

Thanks for posting this. I was using MATLAB on a ssh cluster and was unable to get specgram or spectrogram to work properly. Apparently the built in function uses a MEX file and a FORTRAN file that it was unable to find while running on a remote machine. Your 3D graph is lovely. Thanks again.

[Aragon Burlingham]

 

[anitha padela]

 

[Hoang Lan]

it's useful for me!Thanks

[Loong Zh]

Thanks! It's intuitive for me to learn how STFT works at the sense of programming in Matlab. Thank you!

[sausage Li]

great...but why is the default fs=2?

[xuemin chi]

very helpful thanks!

[Lifang Xue]

It is very useful for a speech researcher.

[ding pei]

thanks a lot .its very helpful!

[Elena Subtirica]

thanks a lot! indeed very useful

[monoj sinha]

 

[sara wu]

thanks a lot

[venata subbu]

e36 y tg

[bouziane mohamed]

 

[ana sari]

 

[Yuan-Tao Weng]

 

[muhammad rafiq]

its a good code for image processing.

[Mitko Orcev]

can someone point me to a java code for such an application?

[Katarzyna Zarnowiec]

very helpful, I used this code in my project, thanks!

[zuo]

thanks for your code