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## Re: [Tftb-help] question about instfreq.m

 From: Eric Chassande-Mottin Subject: Re: [Tftb-help] question about instfreq.m Date: Tue, 25 May 2010 15:18:45 +0200 (CEST) User-agent: Alpine 2.00 (DEB 1167 2008-08-23)

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hi John,

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```fnormhat=0.5*(angle(-x(t+1).*conj(x(t-1)))+pi)/(2*pi);

I agree that the output that I receive from this seems to be correct, but I
cannot find the relationship between these two.  Could someone please
explain to me what I am missing, or point me in the right direction for a
reference to this calculation.
```
```
```
I think what this expression does is simply the finite difference of the phase of the analytic signal.
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if x(t) is the complex-value analytic signal of the data,
denoting its modulus and phase by x(t)=rho(t) exp(i phi(t))

f(t) = 1/2pi dphi(t)/dt ~ (phi(t+delta t) - phi(t-delta t))/(2 delta t)/2 pi.

which is what the above expression says.

cheers,
eric

PS: +pi term is prob. because of phase unwrapping.

```