Forrest Sheng Bao's Cyberhome

by Forrest Sheng Bao http://fsbao.net

I am doing a take-home midterm test of a class I am taking. So, I decided to use Python to to it. Below is a code for one problem. It includes several frequency used functions in classical signal spectral analysis and FIR filter design. The problem itself is to design bandpass filters over alpha to theta bands and apply them onto a EEG series, and plot the time domain and frequency domain signal, as well as the frequency response of filters. I used window methods to design FIR bandpass filters. The filters coefficients are smoothed by a Kaiser window. Filtering is implemented by convolving original signal with coefficients of filters.

by Forrest Sheng Bao http://fsbao.net

The code below is an example on using spectrogram function of MATLAB to compute STFT of a chirp signal, which changes frequency from 10 Hz to 200 Hz in 1 second. Both Hamming and Chebychev windows are used. Different window length has been tried, 128, 64 and 32.

by Forrest Sheng Bao http://fsbao.net

% Copyleft (C) Forrest Sheng Bao 1984-2009 http://fsbao.net
% with Dept. of Electrical and Computer Engineering and Dept. of Computer Science, Texas Tech University, Lubbock, Texas, USA
%
% This program shows the orders and frequency/phase properties of four different kinds of filters, Butterworth, Chebyshev Type I, Chebyshev Type II and Elliptic.
% The filter is expected to have a cutoff frequency at 200 Hz with attenuation 40 db/octave. The sampling frequency is 2000 Hz.
%
% This program licensed in GNU GENERAL PUBLIC LICENSE (GPL) v3 or later.
% If you do not know what GNU GPL is, please visit http://www.gnu.org/copyleft/gpl.html

A friend asked me an interesting question: Why is Z-transform always related to digital filter design? Well, this is interesting. But the clue is simple.

You need a web browser that supports MathML to read this doc. To see whether your browser supports it, please check whether you can see formulas on this page. By default, Linux and Mac user should be able to make it from their Mozilla Firefox browser. For Windows users, well, that's not a question you should ask me.

The author cannot guarantee this article has no typo. Please confirm all equations before you use them.

by Forrest Sheng Bao http://fsbao.net

You need a web browser that supports MathML to read this doc. To see whether your browser supports it, please check whether you can see formulas on this page. By default, Linux and Mac user should be able to make it from their Mozilla Firefox browser. For Windows users, well, that's not a question you should ask me.

The author cannot guarantee this article has no typo. Please confirm all equations before you use them.

There are so many guys asking me the difference between DTFT and DFT. And, they confused these two concepts with FFT and STFT.

by Forrest Sheng Bao http://fsbao.net

Stellate is a company developing EEG sampling and analysis system in Montreal, Canada. Their system is good. But unlike many other software developed in Montreal Neurological Institute, McGill U., it runs on Windows! So, I tried to install it on Linux thru wine, another open source project aiming to run Windows application on Linux. Cool, it is very easy. Just 2 minutes work.

Here displays a short segment of 7 seconds in resolution 7.5 uV/mm.