Re: FFT - Spectrum Analyzer

[Francesco Potortì]

>For a long, non-stationary signal, you probably want to estimate the 
>power spectral density of the generating stochastic process (lots of 
>fancy words). This is done by the computing a "Welch periodogram".
>
>So long story short: type
>
>pwelch(input_signal,hamming(200));
>
>and play aroung with the length of Hamming window until you get the 
>display you want. Octave's pwelch does not seem to plot on a dB scale, 
>so you might want
>
>plot(20*log10(pwelch(input_signal,hamming(200)));

Since this is the power, 10*log10 should be the right way.  Also, the
'db' argument to pwelch should produce a dB plot by itself.  Have a look
at 'help pwelch' for all the options.  Notice that pwelch is part of the
'signal' package, which should be installed in order to use it.

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