[Tftb-help] question about instfreq.m

[John Petro Jr.]

My question is about the instfreq.m file in the toolbox.  I understand instantaneous frequency to be the derivative of the phase of the analytic signal.  In the instfreq.m file the normalized frequency is calculated by:

 

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. 

 

Thank you,

 

John