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2 votes

Why do DFT frequency buckets need to be divided by sample period?

I might be late to this question but the problem with frequency bins isn't about normalization. After your FFT, each frequency bin is calculated as $$ f_k = \frac{k}{N} \cdot f_\mathrm{s} $$ where $f_\...
BoltzBooz's user avatar
  • 159
2 votes

Use DFT (`fft()`) to Replicate 2D Convolution (`conv()`)

HINT ...
Engineer's user avatar
  • 3,012
2 votes
Accepted

Welch method implementation not smooth

myamps = (abs(np.mean(complexData_list,axis=0))**2) Looks like the order of operation here is wrong. You should FIRST calculate the magnitude squared and then take the mean. The PSD is the average of ...
Hilmar's user avatar
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1 vote
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Scaling plots after FFT

Your professor, just like your last question, seems to be providing you with erroneous prompts. His plot shows $\tt{dB}$ values on the y-axis of the FFT plot, but these are actually linear. With that ...
Jdip's user avatar
  • 5,247
1 vote

Is this FIR filter considered symmetric?

Sometimes you need to go back to high-school algebra (assuming you had a good math program in high school). The answer to "Is $f(n)$ symmetric?" is shorthand for "Is $f(n)$ symmetric ...
TimWescott's user avatar
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1 vote

Calculate Total Harmonic Distortion (THD) from FFT Plot

The output of a single-sided DFT such as this is scaled by the number of samples. Therefore, for an input time history that is $N$ samples in length, the DFT at each frequency point returns the ...
ttpjd1's user avatar
  • 11
1 vote
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Characteristics of linear systems in the time and frequency domain

The problem with the third way of doing things is that there is time-domain aliasing happening. To avoid time-domain aliasing using this method, the length of the FFT needs to be $$ N_{\tt fft} = N_{\...
1 vote
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How to calculate a 3D Fourier Transform?

Do not expect to see anything interesting in the Fourier transform spectra, whether 3D or 1D spectra, of forced oscillations with resonant frequency. Any natural oscillations that may (and should) ...
V.V.T's user avatar
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1 vote

Physical interpretation of frequency domain data of signal noise

The Fourier transformation attempts to imitate a signal using a selectable number of sin and cos functions. Since the sin/cos functions for $t \to\pm\infty$ do not disappear asymptotically, the signal ...
9herbert9's user avatar
1 vote
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Physical interpretation of frequency domain data of signal noise

The results of the Fourier Transform(s) generally produce a "spectral density". For the Discrete Fourier Transform the spectrum has the same units as the original signal, i.e. Volts in your ...
Hilmar's user avatar
  • 42.7k
1 vote

Physical interpretation of frequency domain data of signal noise

Compute the magnitude: $$|X_f| = \sqrt{(\Re(X_f))^2 + (\Im(X_f))^2}$$ Depending on the scaling used by your FFT routine, you might have to scale the result by the length of your FFT. I suggest you try ...
Jdip's user avatar
  • 5,247

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