how can i plot the amplitude spectrum centered at the zeroth frequency.

Hi. I have fft of vector and i wanna know how can i plot the amplitude spectrum centered at the zeroth frequency.

I attached the file which i load to matlab.

I wrote this below. And i wanna plot its amplitude spec at zeroth freq.

"

load data.mat

X= fft(x)

"

Answer 1

[Nithin]

Hi Batuhan,

I understand that you have a FFT of vector and want to know the process of plotting the amplitude spectrum centered at the zeroth frequency.

To implement this, kindly refer to the following steps -

1. Obtain your signal in the time domain.

2. Compute the Fourier Transform of the signal using the "fft" function.

X = fft(x); % Assuming your signal is stored in a variable 'x'

3. Shift the zero frequency component to the center of the spectrum using "fftshift" function.

X = fftshift(X);

4. Compute the amplitude spectrum by taking the absolute value of the shifted spectrum.

amplitude_spectrum = abs(X);

5. Create a frequency vector that corresponds to the frequency components of the spectrum. Use the "linspace" function to create a linearly spaced frequency vector.

N = length(x);
fs = 1; % Assuming a sampling frequency of 1 Hz
frequencies = linspace(-fs/2, fs/2, N);

6. Plot the amplitude spectrum centered at the zeroth frequency.

plot(frequencies, amplitude_spectrum);
xlabel('Frequency (Hz)');
ylabel('Amplitude');
title('Amplitude Spectrum Centered at Zero Frequency');

For more information regarding "fft" and "fftshift" functions, kindly refer to the following documentation:

https://in.mathworks.com/help/matlab/ref/fft.html

https://in.mathworks.com/help/matlab/ref/fftshift.html

I hope this answer resolves your query.

Regards,

Nithin Kumar.

[Paul]

Hi Nithin,

The expression for "frequencies" is not correct. See this Question for more discussion.