[matlab]: FFT related problems

1、 fft Amplitude in

DC component ：abs(X[0])/N
Components of other frequency points ： abs(X[f])/（N/2）
Amplitude rotation db Pay attention to pow2db（） and db（） Usage of , The former is power , The latter is amplitude .
Here's the specific fft Program , The program is more general for non DC components fft Amplitude value of

function fft_plot(y,fs,s_name)
   % L_i = length(y)*100;
    L_i = 2^nextpow2(length(y)*100);
    s_i_fft = fft(y,L_i);
    s_i_fftshfit = fftshift(s_i_fft);
    P = abs(s_i_fftshfit/length(y))*2;   % For non DC components or 0 It's divided by N multiply 2, For the DC component, it is directly divided by N 
%     fshift = (-L_i/2:L_i/2-1)*(fs/L_i);
    fshift = linspace(-fs/2,fs/2,L_i);
    figure;
    plot(fshift,P);
    title([s_name,' Bilateral spectrum of  ']);
    xlabel('f (Hz)');
    ylabel('|P(f)|');
end

2 、 reference

1. FFT Why is the amplitude spectrum wrong , Need correction
2. fft After the operation, you need to multiply the amplitude 2 except N（ The number of transformed points ） Explanation （Matlab）
3. FFT Determination of frequency and amplitude of
4. Matlab in IFFT/FFT Precautions and in OFDM Application problems in simulation