Comments on: Interpret FFT results – obtaining magnitude and phase information https://www.gaussianwaves.com/2015/11/interpreting-fft-results-obtaining-magnitude-and-phase-information/ Signal Processing for Communication Systems Thu, 27 Jul 2023 05:42:21 +0000 hourly 1 https://wordpress.org/?v=6.6.2 By: Shrikant https://www.gaussianwaves.com/2015/11/interpreting-fft-results-obtaining-magnitude-and-phase-information/#comment-46579 Thu, 18 Aug 2022 18:04:25 +0000 http://www.gaussianwaves.com/?p=10899#comment-46579 Why the amplitude in frequency domain is half of that in time domain?

]]> By: Mathuranathan https://www.gaussianwaves.com/2015/11/interpreting-fft-results-obtaining-magnitude-and-phase-information/#comment-45500 Wed, 15 Sep 2021 03:45:08 +0000 http://www.gaussianwaves.com/?p=10899#comment-45500 In reply to Prithvi S.

The fundamentals are same for 2D Fourier transform. Its just that one more dimension is added to the processing. I suggest looking at this article
https://people.ciirc.cvut.cz/~hlavac/TeachPresEn/11ImageProc/12FourierTxEn.pdf

]]> By: Prithvi S https://www.gaussianwaves.com/2015/11/interpreting-fft-results-obtaining-magnitude-and-phase-information/#comment-45475 Thu, 02 Sep 2021 05:39:51 +0000 http://www.gaussianwaves.com/?p=10899#comment-45475 Hi Mathuranathan,
Thanks for such an amazing article. It is very helpful in interpreting the data and understanding the Fourier Transform. Would you please help me interpreting the same for a 2D Fourier transform? Or can you please share any articles related to the 2D FFT or fft2(). It would be of great help.
Thanks again for such a vivid explanation of fft function.

]]> By: Mathuranathan https://www.gaussianwaves.com/2015/11/interpreting-fft-results-obtaining-magnitude-and-phase-information/#comment-44912 Sat, 20 Mar 2021 04:54:14 +0000 http://www.gaussianwaves.com/?p=10899#comment-44912 In reply to Jan.

Glad it worked for you!! Thank you !!!

]]> By: Jan https://www.gaussianwaves.com/2015/11/interpreting-fft-results-obtaining-magnitude-and-phase-information/#comment-44911 Fri, 19 Mar 2021 22:58:48 +0000 http://www.gaussianwaves.com/?p=10899#comment-44911 The phase noise was driving me nuts! Already suspected something fishy with rounding errors but to no avail. The atan2 function did the trick for me! Thanks a lot!

]]> By: Mathuranathan https://www.gaussianwaves.com/2015/11/interpreting-fft-results-obtaining-magnitude-and-phase-information/#comment-43911 Mon, 24 Aug 2020 03:39:33 +0000 http://www.gaussianwaves.com/?p=10899#comment-43911 In reply to MARTIN THOMAS.

The length of the phase vector (derived from FFT output) depends on the FFT length (N). In the example above the FFT length is set to 256. So it gives 256 phase values corresponding to 256 frequency bins.

]]> By: MARTIN THOMAS https://www.gaussianwaves.com/2015/11/interpreting-fft-results-obtaining-magnitude-and-phase-information/#comment-43910 Mon, 24 Aug 2020 03:13:37 +0000 http://www.gaussianwaves.com/?p=10899#comment-43910 While doing the phase calculation from the above equation why i am getting more values than the input? I need that in same length.

]]> By: Mathuranathan https://www.gaussianwaves.com/2015/11/interpreting-fft-results-obtaining-magnitude-and-phase-information/#comment-43719 Thu, 16 Jul 2020 08:08:48 +0000 http://www.gaussianwaves.com/?p=10899#comment-43719 In reply to heyjoe.miller.

This is due to spectral leakage phenomenon. You may read about it here
https://www.gaussianwaves.com/2011/01/fft-and-spectral-leakage-2/

Due to spectral leakage, you will see non-zero values for frequency components that are near the frequency of the signal. This will also reflect in the phase spectrum.

Set Fs=100 and N=length(x) (length(x)= 640 and it is not a power of 2). Now you will observe perfect frequency spectrum. However, if you change N=power of 2, spectrum will be affected by spectral leakage.

]]> By: heyjoe.miller https://www.gaussianwaves.com/2015/11/interpreting-fft-results-obtaining-magnitude-and-phase-information/#comment-43718 Wed, 15 Jul 2020 16:41:42 +0000 http://www.gaussianwaves.com/?p=10899#comment-43718 This example worked well until I changed the signal frequency and found the computed phase only to be correct when the sampling frequency is exactly a power of 2 higher than the signal frequency(x4,8,16,32,64 etc) otherwise it not correct. Is there some other correction that needs to be performed to the result in these cases?

]]> By: anon https://www.gaussianwaves.com/2015/11/interpreting-fft-results-obtaining-magnitude-and-phase-information/#comment-43036 Wed, 01 Apr 2020 10:34:33 +0000 http://www.gaussianwaves.com/?p=10899#comment-43036 I loved this explanation. Really simple overview of FFT results. Plus, learned about phase, and all the tricks to view it properly. Beautifully done.

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