When I plot said function output, "p," it looks like a typical spectrum with an easily identifiable peak at a given ix on the x axis. The help rubric from the function is
SYNTAX: p = mesa(x,m,nfreq); For a vector x, this function calculates a maximum-entropy spectrum of order m. The spectral estimate is returned in the vector p, which has nfreq points linearly spaced in the Nyquist frequency interval 0-.5. The psd is normalized such that the mean square value of x equals the integral of p from -.5 to .5, so sum(x.^2)/N ~= sum(p)/nfreq. Mesa is based on the Burg algorithm, as described in Numerical Recipes and implemented in their memcof and evlmem subroutines. Written by Eric Breitenberger Version 5/24/95
My problem is that the x axis is unitless, i.e. if nfreq = 200 then the x axis is 1 to 200 long. If the peak is at x axis ix = 22, for example, how do I calculate the measured frequency/period of the input signal "x"?
To give a concrete example:
the length of the input vector "x" is 20 because I believe (or know due to a controlled input experiment) this length vector contains one full cycle (noisy sinusoidal) of interest
order m is set to 10, for example, although this is incidental to my question as I can see from experiment that changing the value of m only affects the sharpness of the peak
nfreq is set to 200
and with these values the peak occurs at x axis ix == 22.
From this, what is the mathematics to get the measured frequency/period from the output of the function?
input_x = awgn( sinewave( 20 , 20 ) , 10 ) ;