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## Re: Spectrum Estimate functions

 From: E. Joshua Rigler Subject: Re: Spectrum Estimate functions Date: 07 May 2003 10:19:49 -0600

```These spectrum analysis functions are great!  I can't believe I never
noticed them before.  Oh well, I guess I learned more by writing my own
similar functions before finding these.

I have a question though.  What exactly is the difference between the
pyulear and pburg functions?  I get power spectrum estimates that are
similar in shape and scale (using the same inputs, obviously), but
offset by nearly 40 dB!  Try this:

[b,a] = cheby1(4,3,[0.2, 0.4]);
pyulear(filter(b,a,randn(2^12,1)),2,'db');
hold
pburg(filter(b,a,randn(2^12,1)),2,'db');

Are these results to be expected?  I'm afraid I don't really know what
the difference is between the Yule-Walker and Burg methods of
determining an AR model.  When I use my own techniques for determining
the AR model (either based on correlation functions, or a
straight-forward linear regression), and plot their frequency response
with __power, I get results that are actually ~half-way between the
two!  (...and yes, I ran these tests with the same input time series,
derived from the coefficients set in the example above).

These offsets just seem a little suspicious.  I also tried this with
p=3, and got similar results, although the peak response from pyulear
seemed to shift very slightly to the right.

-EJR

On Tue, 2003-05-06 at 18:37, Paul Kienzle wrote:
>
> See pwelch.m from octave-forge:
>
> http://octave.sourceforge.net/index/signal.html#Powerspectrumanalysis
>
> Paul Kienzle
>

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