Here is my code for generating a triangular waveform in the time domain and for generating its corresponding fourier series/transform (I don't know whether its series or transform because matlab only has fourier transform function but since the signal is periodic, references say that the fourier counterpart must be called fourier series).
x = 0; s = 50; % number of sinusoidal components fs = 330; % hertz dt = 1/fs; % differential time t = [0:dt:4]; % seconds const = 2 / (pi^2); for k = 1:2:s, x = x + (((-1)^((k - 1) / 2)) / (k^2)) * sin(4*pi*k*t); end x = const * x; % amplitude = max(x) = 0.2477 % period = 0.5 seconds f = linspace(-fs/2,fs/2,length(x)); xk = fftshift(fft(x)); figure; subplot(3,1,1); plot(t,x); grid on; xlabel('time(seconds)'); title('Time Domain'); subplot(3,1,2); plot(f,abs(xk)); grid on; xlabel('frequency(hertz)'); title('Magnitude Spectrum'); subplot(3,1,3); plot(f,angle(xk)); grid on; xlabel('frequency(hertz)'); title('Phase Spectrum');
And here is the generated plots for the time domain signal, magnitude spectrum, and phase spectrum.
link: fs = 330hz
My problem is when I changed the sampling frequency (fs which is currently equal to 330 hz) to another value, the plots of the magnitude and phase spectra change.
Here is the plots of the magnitude and phase spectra when the sampling frequency is equal to 400 hz:
link: fs = 400 hz
Can you explain why does this happen? And what can I do in order to get a constant plots for the magnitude and phase spectra given any sampling frequency?