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

[Eric Chassande-Mottin]

hi John,

> 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.

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.