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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)

hi John,


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.

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.


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

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