Fft code; differences between scripts.

Question

Guglielmo Giambartolomei 2016-10-11

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/306756-fft-code-differences-between-scripts

Goodmorning everyone, I want to perform a fft of an accelerometric signal and I'd like to know what's the best way to do that. What script is more correct?

Code 1:

%%Time domain analysis of channel 2 
x2=x0(:,3);
N2=length(x2);
Fs=2400;
T=1/Fs;
t2=linspace(0,N2*T,N2);
figure
plot(t2,x2)
grid on
title('Acc. on the sparger (ch. 2)')
xlabel('t (s)')
ylabel('x2(t), Acceleration (g)')
%%Frequency domain analys of channel 2
xdft2=fft(x2-mean(x2))/N2;
xdft2=xdft2(1:floor(N2/2)+1);
freq2=0:Fs/length(x2):Fs/2;
figure;
plot(freq2,abs(xdft2))
grid on
title('Single-Sided Amplitude Spectrum of x2(t)')
xlabel('f (Hz)')
ylabel('X2(f)')

Code 2:

x2=x0(:,3);
Fs = 2400;                    % Sampling frequency
T = 1/Fs;                     % Sample time
N2=length(x2);                % Length of signal
t=(0:N2-1)*T;                 % Time vector
% Time domain analysis
plot(t,x2)
NFFT = 2^nextpow2(N2); % Next power of 2 from length of y
Y = fft(x2,NFFT)/N2;
f = Fs/2*linspace(0,1,NFFT/2+1);
% Plot single-sided amplitude spectrum.
figure
plot(f,2*abs(Y(1:NFFT/2+1))) 
title('Single-Sided Amplitude Spectrum of y(t)')
xlabel('Frequency (Hz)')
ylabel('|Y(f)|')