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Re: Dynamic Spectrum [message #60578 is a reply to message #60574]

Mon, 02 June 2008 17:20

russell.grew
Messages: 74
Registered: February 2005

Member

You might want to have a read of

Welch, 'The Use of Fast Fourier Transform for the Estimation of Power
Spectra: A Method Based on Time Averaging Over Short, Modified
Periodograms', IEEE Trans. Audio & Electroacoust., Volume AU-15, p.
70-73.

It's probably the simplest implementation of what you are trying to
do. It provides for overlapping FFT's and discusses windowing and
their compensation. Also theres a book by Hayes, 'Statistical Digital
Signal Processing and Modeling' that has a good chapter on power
spectrum estimation.

To get your y-axis correct you need to know the data sample rate and
hence evaluate the Nyquist frequency. For instance if your data is
sampled twice per second, you can only plot up to 1 Hz. The kHz data
in the link you gave obviously requires large sample rates. You need
to choose your FFT length to give an appropriate frequency resolution
to see what you are looking for in the data (if you have a 100 point
FFT over data with a 1 Hz Nyquist and drop the imaginary half of the
FFT, you are left with 1/50 = 0.02 Hz frequency resolution).

Fun times.

Russell.

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[Message index]

		Re: Dynamic Spectrum By: pgrigis on Tue, 03 June 2008 06:24
		Re: Dynamic Spectrum By: russell.grew on Mon, 02 June 2008 17:20
		Re: Dynamic Spectrum By: R.G. Stockwell on Mon, 02 June 2008 09:16
		Re: Dynamic Spectrum By: jdu on Mon, 02 June 2008 06:17
		Re: Dynamic Spectrum By: lasse on Mon, 02 June 2008 02:59
		Re: Dynamic Spectrum By: duxiyu@gmail.com on Mon, 02 June 2008 02:23
		Re: Dynamic Spectrum By: lasse on Mon, 02 June 2008 01:39
		Re: Dynamic Spectrum By: David Fanning on Sun, 01 June 2008 20:44

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