signal processing - How to implement the order analysis in MATLAB -

i have audio file represents sound of motor. i've been reading 'normal' fft doesn't deliver valuable analysis machine, , should use order analysis describe 'behavior' of machine. recorded sound while incrementing speed, , put records , calculated spectogram. here code that:

%% read audio file , plot  clear, clc , clf; m = 512; k =1  data= 0 ;    =100:5:180     filename =['a10_usp0_mic100k_2nd_v_',int2str(i),'.wav']     [x(:,k),fs] = audioread(filename);     k = k+1 ; end = 1:length(x(1,:))     data = [data(:);x(:,i)]; end  k = length(x(1,:));     while k ~= 2    data = [data(:);x(:,k)];    k = k -1;     end spectrogram(data,hamming(m),m/2,0:20:4000,fs,'yaxis'); 

and result looks like:

as might able see, incremented speed of machine 5 each timepoint. question how calculate order analysis system!? help!

this more of scientific question question programming. order analysis can done using fourier transform. need looking diagonal lines in output, i.e. frequency of noise proportional rotation speed.

in example image there such order 2000 hz @ time(speed) 0 4000 hz @ time(speed) 150. afterwards seems reflected downwards, artifact of insufficient sampling.

so order it? need know rotational speed of motor not seem know. there weaker order starting @ 3000 hz @ time(speed) 0. 2 or more visible orders might able deduce rotational speed of motor (by requiring frequencies whole number multiples of original speed).

anyway code doesn't need changed except higher frequency resolution.