在命令視窗輸入doc fft回車後，可看到例子。%構造出訊號（如已有訊號，此步可省略）Fs = 1000; % Sampling frequencyT = 1/Fs; % Sample timeL = 1000; % Length of signalt = (0:L-1)*T; % Time vector% Sum of a 50 Hz sinusoid and a 120 Hz sinusoidx = 0.7*sin(2*pi*50*t) + sin(2*pi*120*t); y = x + 2*randn(size(t)); % Sinusoids plus noiseplot(Fs*t(1:50),y(1:50))title("Signal Corrupted with Zero-Mean Random Noise")xlabel("time (milliseconds)")NFFT = 2^nextpow2(L); % Next power of 2 from length of yY = fft(y,NFFT)/L;f = Fs/2*linspace(0,1,NFFT/2+1);%FFT分析% Plot single-sided amplitude spectrum.plot(f,2*abs(Y(1:NFFT/2+1))) title("Single-Sided Amplitude Spectrum of y(t)")xlabel("Frequency (Hz)")ylabel("|Y(f)|")
在命令視窗輸入doc fft回車後，可看到例子。%構造出訊號（如已有訊號，此步可省略）Fs = 1000; % Sampling frequencyT = 1/Fs; % Sample timeL = 1000; % Length of signalt = (0:L-1)*T; % Time vector% Sum of a 50 Hz sinusoid and a 120 Hz sinusoidx = 0.7*sin(2*pi*50*t) + sin(2*pi*120*t); y = x + 2*randn(size(t)); % Sinusoids plus noiseplot(Fs*t(1:50),y(1:50))title("Signal Corrupted with Zero-Mean Random Noise")xlabel("time (milliseconds)")NFFT = 2^nextpow2(L); % Next power of 2 from length of yY = fft(y,NFFT)/L;f = Fs/2*linspace(0,1,NFFT/2+1);%FFT分析% Plot single-sided amplitude spectrum.plot(f,2*abs(Y(1:NFFT/2+1))) title("Single-Sided Amplitude Spectrum of y(t)")xlabel("Frequency (Hz)")ylabel("|Y(f)|")