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## Re: avgpower in Octave?

 From: Francesco Potorti` Subject: Re: avgpower in Octave? Date: Thu, 19 Mar 2009 18:13:13 +0100

```>Matlab 2007b (7.5.0) has an avgpower function. From
>http://www.mathworks.com/products/signal/demos.html?file=/products/demos/shipping/signal/spectralanalysisobjsdemo.html:
>
>"The avgpower method uses a rectangle approximation to the integral to
>calculate the signal's average power using the PSD data stored in the
>object.
>
>"The avgpower method returns the average power of the signal which is
>the area under the PSD curve."
>
>Example invocation:
>
>    numSamples = 10000
>    frequency = 20
>    amplitude = 10
>    Fs = 1000
>    t = [0:1/numSamples:1];
>    sig = amplitude * sin(2*pi*frequency*t);
>    h = spectrum.periodogram('rectangular');
>    hopts = psdopts(h, signal);
>    set(hopts,'Fs',Fs);
>    p = psd(h,signal,hopts);
>    lower = 12
>    upper = 30
>    beta_power = p.avgpower([lower upper]);
>
>I am looking to replicate this sort of functionality in Octave. The
>function "pwelch" seems like a possibility.

You use pwelch to compute the PSD.  It is compatible with Matlab's.

>                                            To wit:
>
>    ...
>    sig = amplitude * sin(2*pi*frequency*t);
>    pwelch('R12+');
>    [spectra, freq]=pwelch(signal, [], [], [], Fs, plot_type='dB');
>
>Now I *think* spectra has the y values of the PSD and freq has the x
>values. So, I could find the samples in freq that fall between "lower"
>and "upper" and .. er, average the corresponding values in spectra?

You should compute the integral, so I think that you can average them
and multiply by upper-lower, if upper and lower are frequencies as they
appear to be.

>Moreover, the values in "spectra" don't necessarily correspond to my
>desired upper and lower, and I'm not sure what to do about that.

I do not follow you here.

>It might also be possible to get a single value from some sort of FFT
>instead of using pwelch.

You want to compute the power is a given range of frequencies, if I
understand correctly.  So you must first estimate the PSD, which is why
you need pwelch.

--
Francesco Potortì (ricercatore)        Voice: +39 050 315 3058 (op.2111)
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