Greetings all
I have a frequency domain plot that plots but the amplitude doesn't match
the equation at all. In the example I have the amplitude set to 8 but when I plot it the amplitude
shows up as 30+ why is this?
tia sal22
code below:
Fs = 1000; % Sampling frequency
t=linspace(0,1,1000);
vp_sig_orig=8*sin(2*pi*2*t)
vp_sig_len=length(vp_sig_orig);
% Use next highest power of 2 greater than or equal to length(x) to calculate FFT.
nfft= 2^(nextpow2(length(vp_sig_orig)));
% Take fft, padding with zeros so that length(fftx) is equal to nfft
fftx = fft(vp_sig_orig,nfft);
% Calculate the numberof unique points
NumUniquePts = ceil((nfft+1)/2);
% FFT is symmetric, throw away second half
fftx = fftx(1:NumUniquePts);
% Take the magnitude of fft of x and scale the fft so that it is not a function of the length of x
mx = abs(fftx)/length(vp_sig_orig);
% Take the square of the magnitude of fft of x.
mx = mx.^2;
% Since we dropped half the FFT, we multiply mx by 2 to keep the same energy.
% The DC component and Nyquist component, if it exists, are unique and should not be multiplied by 2.
if rem(nfft, 2) % odd nfft excludes Nyquist point
mx(2:end) = mx(2:end)*2;
else
mx(2:end -1) = mx(2:end -1)*2;
end
% This is an evenly spaced frequency vector with NumUniquePts points.
freq_vect = (0:NumUniquePts-1)*vp_sig_len/nfft;
% Generate the plot, title and labels.
subplot(2,1,1),plot(t,vp_sig_orig)
title('Time domain plot');
xlabel('time');
ylabel('Power');
plot_len=1000;%length to plot
subplot(2,1,2), plot(freq_vect(1:end),mx(1:end))
title('Power Spectrum of vp');
xlabel('Frequency (Hz)');
ylabel('Power');
