MATLAB: Instantaneous Frequency

Question

Hello

I am estimating the Instantaneous Frequency of my signal using the following code.

h=hilbert(acc);
unrolled_phase = unwrap(angle(h));
inst_freq = ((diff(unrolled_phase))'./diff(T))/(2*pi);

I get both positive and negative frequencies (very few) also some spikes. How to avoid negative frequency and unrealistic. frequencies?

Answer 1

Your problems are coming from the unwrapping of the phase. Your estimate of the instantaneous frequency can only be negative if diff(unrolled_phase) is negative. Just add 2pi to those points (and all the values after).